Earth observation glossary

A 

Above ground biomass 

Above ground biomass refers to the total mass of living plant material present above the soil surface in a specific area or ecosystem. This includes the combined weight of plant stems, leaves, branches and other aerial parts of plants. Above ground biomass is a critical metric for assessing the quantity of carbon stored in vegetation and plays a key role in understanding the carbon cycle and ecosystem dynamics.

Aeolus 

Aeolus is ESA’s first satellite mission which acquired profiles of Earth's wind on a global scale. These observations are used to improve weather forecasts and climate models. The Aeolus satellite carries just one large instrument – a Doppler wind lidar that measures the winds sweeping around our planet.

Aerosol 

Particles of liquid or solid dispersed as a suspension in gas. These tiny particles or droplets can remain suspended in the air for an extended period.

Air pollution 

Air pollution refers to the presence of harmful substances or pollutants in the air that can be detrimental to the health of living organisms and the environment. These pollutants can include gases, particles, and other materials, often resulting from human activities such as industrial processes, vehicle emissions and the burning of fossil fuels.

Albedo 

Albedo is a measure of the reflectivity of a surface, indicating how much sunlight it reflects back into space. It is often expressed as a percentage, with higher albedo values indicating greater reflectivity. For example, a surface with high albedo, like snow, reflects more sunlight, while a surface with low albedo, like asphalt, absorbs more sunlight.

Algae

Algae are a diverse group of aquatic, plant-like organisms that range in size from single-celled microalgae to large seaweeds. They are found in a wide range of aquatic environments, from freshwater to saltwater, and are important primary producers in aquatic ecosystems, converting energy from the Sun into organic matter through photosynthesis. Some types of algae can also cause harmful algal blooms that can have negative impacts on human health and the environment.

Algal blooms 

Algal blooms are rapid and excessive growths of algae in water bodies, such as lakes or oceans. These blooms can be triggered by an abundance of nutrients, often from factors like agricultural runoff or wastewater discharge. The overgrowth of algae can lead to the formation of dense, visible patches on the water's surface. While some algae are harmless, certain types of algal bloomscan produce toxins harmful to aquatic life and pose risks to human health.

Altimeter 

An altimeter is a device used to measure the altitude or height above a specific reference point, usually Earth's surface. Altimeters are commonly used in satellite missions to monitor changes in sea level, ice thickness and terrain topography for various Earth observation applications.

Altius

The Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere (Altius) mission carries a high-resolution spectral imager and uses a limb-sounding technique to deliver profiles of ozone and other trace gases in the upper atmosphere to support services such as weather forecasting, and to monitor long-term trends.

Anomaly

An anomaly refers to something that deviates from what is considered normal, expected, or standard. In various fields, including science, statistics, and everyday language, an anomaly is an observation or occurrence that stands out or differs significantly from the usual patterns or trends.

Anthropogenic

Anthropogenic refers to anything that is caused or produced by human activity or influence. It is a term used to describe the effects of human actions on the environment, including climate change, pollution, deforestation and other forms of environmental degradation.

Arctic Circle

The Arctic Circle is an imaginary line of latitude located approximately 66.5 degrees north of the equator. It marks the southernmost boundary where, at least once a year during the winter solstice, the sun does not rise above the horizon for a full 24 hours, and during the summer solstice, it does not set for a full 24 hours.

Arctic Weather Satellite

The Arctic Weather Satellite mission provides frequent coverage of Earth for improved nowcasting and numerical weather prediction. Carrying a cross-track scanning microwave radiometer, the Arctic Weather Satellite mission provides measurements of atmospheric humidity and temperature.

Artificial intelligence (AI)

A field of research in computer science that develops methods and software for machines to perceive their environment and use learning and intelligence to take actions.

Artificial Intelligence for Earth Observation (AI4EO)

Artificial Intelligence for Earth Observation (AI4EO) describes the use of AI models to extract information from satellite data. Example applications include interpreting and understanding remote sensing imagery, analysing Big Data and digital twins. 

Atmosphere

The atmosphere is the envelope of gases that envelops a celestial body, and on Earth, it consists of several distinct layers. The innermost layer, closest to the Earth's surface, is the troposphere, where weather events and phenomena like clouds occur. This layer is primarily composed of nitrogen and oxygen, along with trace amounts of other gases.

Above the troposphere is the stratosphere, which contains the ozone layer, crucial for blocking harmful ultraviolet radiation. The composition of the atmosphere also includes gases like carbon dioxide, methane, and water vapor.

Beyond the stratosphere, the mesosphere and thermosphere extend into the outermost layers.

These atmospheric layers collectively play a crucial role in protecting life on Earth by absorbing harmful solar radiation, regulating temperatures, and facilitating various atmospheric processes essential for the planet's habitability.

Atoll

An atoll is a circular or oval-shaped reef structure with a lagoon in the centre. These structures typically form around a volcanic island that has subsided while the coral grows upwards. Atolls are common in the Indian and Pacific Oceans.

B 

Backscatter

Backscatter refers to the reflection of energy or signals, such as radar waves or lidar pulses, back towards the sensor or instrument after interacting with Earth's surface.

Barometer

An instrument used to measure atmospheric pressure.

Biodiversity

Biodiversity refers to the variety of life on Earth at different levels, including the diversity of species, ecosystems, and genetic variation within species.

Biomass

Biomass refers to the total mass of living or recently living organisms in a given area or ecosystem, typically expressed in terms of weight per unit area or volume. It includes plant material, animal matter, microorganisms and other organic substances.

Biomass (mission)

ESA’s Biomass mission will provide crucial information about the state of our forests and how they are changing. The data will be used to further our knowledge of the role forests play in the carbon cycle.

Biosphere

The biosphere is the part of Earth where living organisms exist. It encompasses allecosystems, including the atmosphere, hydrosphere (water bodies), lithosphere (land), and their interactions.

Boreal

Boreal refers to the northernmost biome or region characterised by cold climates and dominated by coniferous forests, such as spruce, fir, and pine trees. The boreal zone spans across the northern latitudes of North America, Europe, and Asia.

C 

Cal/Val

Calibration and Validation.

Calibration

Calibration involves adjusting and validating the accuracy of sensor measurements by comparing them to a known standard. This crucial process ensures that the satellite instruments provide reliable and consistent data for scientific analysis, remote sensing, and Earth observation applications.

CAMS

Copernicus Atmosphere Monitoring Service.

Carbon cycle

The carbon cycle is the continuous and natural exchange of carbon compounds between the atmosphere, oceans, soil and living organisms on Earth. It involves processes such as photosynthesis, respiration, decomposition and combustion, influencing the distribution and cycling of carbon in various forms like carbon dioxide and organic matter.

Carbon dioxide

Carbon dioxide is a colourless and odourless gas composed of one carbon atom and two oxygen atoms. It is a crucial component of Earth's atmosphere, resulting from natural processes like respiration and combustion, as well as human activities such as the burning of fossil fuels. Carbon dioxide plays a significant role in the Earth's carbon cycle and is a key greenhouse gas, influencing the planet's climate by trapping heat in the atmosphere.

Carbon sequestration

The process of capturing and storing carbon dioxide from the atmosphere. For example, trees and plants absorb carbon dioxide, release the oxygen and store the carbon.

Celsius

Celsius, often denoted as °C, is a unit of temperature measurement and is one of the most widely used temperature scales globally. The Celsius scale sets the freezing point of water at 0 degrees and the boiling point at 100 degrees.

CHIME

The Copernicus Hyperspectral Imaging Mission for the Environment, or CHIME, is being developed to support EU policies on the management of natural resources – ultimately helping to address the global issue of food security.

CHIME will carry a unique visible to shortwave infrared spectrometer to provide routine hyperspectral observations to support new and enhanced services for sustainable agricultural and biodiversity management, as well as soil property characterisation. CHIME is one of six Copernicus Sentinel Expansion missions that ESA is developing on behalf of the EU. 

Chlorofluorocarbon (CFC)

Chlorofluorocarbons are a family of organic compounds that contain carbon, chlorine and fluorine atoms. They were widely used as refrigerants, solvents and propellants in aerosol cans and other consumer products until the 1980s, when it was discovered that they were contributing to the depletion of Earth's ozone layer. CFCs are very stable and can remain in the atmosphere for several decades, where they can react with and destroy ozone molecules. This can lead to the formation of an ozone hole over the polar regions, which can have serious consequences for human health and the environment. In response to these concerns, the use of CFCs was phased out under the Montreal Protocol, an international treaty signed in 1987. Since then, the concentration of CFCs in the atmosphere has been gradually declining, and the ozone layer is expected to recover over the coming decades.

Chlorophyll

Chlorophyll is a green pigment found in the chloroplasts of plant cells and other photosynthetic organisms. It plays a fundamental role in photosynthesis by capturing light energy and converting it into chemical energy, allowing plants to produce carbohydrates from carbon dioxide and water in the presence of sunlight. Chlorophyll's green colour arises from its ability to absorb light most efficiently in the blue and red regions of the electromagnetic spectrum while reflecting green light.

CIMR

The Copernicus Imaging Microwave Radiometer mission (CIMR) will provide measurements to decision makers with evidence of change and impact in the polar regions – with a focus on the Arctic.

The mission has the largest radiometer developed by ESA and will provide high-resolution measurements related to sea ice, the ocean, snow and ice-sheet surfaces. This will be crucial in understanding the evolution of the climate in the polar region. CIMR is one of six Copernicus Sentinel Expansion missions that ESA is developing on behalf of the EU. 

Climate

Climate is the weather in a specific area over a long period of time – usually 30 years of more.

Climate change

Climate change refers to long-term alterations in temperature, precipitation and other atmospheric conditions on Earth. It is often associated with shifts in global or regional climate patterns, including variations in temperature extremes, sea level rise and changes in the frequency and intensity of weather events. Climate change can result from natural processes or human activities, particularly the emission of greenhouse gases like carbon dioxide from the burning of fossil fuels and deforestation.

Climate Change Initiative (CCI)

Climate Change Initiative (CCI) is a programme that aims to provide long-term, high-quality climate data records from satellite observations. ESA's CCI focuses on essential climate variables, including those related to Earth's atmosphere, oceans and land surfaces. The initiative involves the generation, validation and distribution of climate data records to support climate research, monitoring and assessment. By utilising satellite data, the ESA Climate Change Initiative contributes valuable information for understanding climate change trends, variability and impacts on a global scale.

Climate model

A climate model is a computer-based representation of Earth's climate system that simulates the interactions and behaviours of the atmosphere, oceans, land surface and other components. These models use mathematical equations to project and analyse climate patterns, providing insights into future climate conditions based on various scenarios and input parameters. Climate models are valuable tools to study and understand the complex dynamics of Earth's climate, assess the impacts of different factors and make projections about potential future climate changes.

Climate system

The climate system refers to the complex interaction of various components on Earth, including the atmosphere, oceans, land surfaces, ice masses and living organisms. These interconnected elements influence and regulate the planet's climate by exchanging energy, heat and moisture. Changes in one component can have cascading effects on the entire system, leading to alterations in weather patterns and long-term climate trends. Understanding the dynamics of the climate system is crucial for comprehending climate processes and predicting the impacts of natural variability and human-induced changes.

Climate tipping points

Climate tipping points are elements of the Earth system in which small changes can kick off reinforcing loops that ‘tip’ a system from one stable state into a profoundly different state.

Climatology

Science dealing with climate and climate phenomena.

Clouds

Clouds are visible masses of tiny water droplets or ice crystals suspended in Earth's atmosphere. Formed through the process of condensation or sublimation, clouds can take various shapes and sizes, ranging from wispy cirrus clouds high in the atmosphere to dense cumulus clouds often associated with thunderstorms. Clouds play a crucial role in the planet's energy balance by reflecting sunlight back into space and trapping heat, contributing to weather patterns and influencing climate.

CO2M

The Copernicus Anthropogenic Carbon Dioxide Monitoring (CO2M) mission will be the first satellite mission to measure how much carbon dioxide is released into the atmosphere through human activity.

CO2M is a crucial step in our commitment to understanding and mitigating climate change. It will offer unprecedented precision in monitoring carbon dioxide emissions from the combustion of fossil fuel at national and regional scales.

Its data will provide the EU with a unique and independent source of information to assess the effectiveness of policy measures and to track their impact towards decarbonising Europe ahead of the next Global Stocktake set to place in 2028. CO2M is one of six Copernicus Sentinel Expansion missions that ESA is developing on behalf of the EU. 

Condensation

Condensation refers to the change of a substance to a denser form, such as a gas to a liquid.

Contrails

Contrails, short for condensation trails, are visible streaks of ice crystals or water droplets that form in the wake of aircraft flying at high altitudes. These trails result from the condensation of water vapor present in the aircraft's exhaust gases when they come into contact with the cold air at high altitudes.

Convection

Convection is the process of heat transfer within Earth’s atmosphere. When a specific air mass is heated, it becomes less dense and rises, creating upward air currents. As the air rises, it cools, becomes denser, and eventually descends back to the surface. Convection causes local breezes, winds and thunderstorms.

COP

Conference of the parties. The COP is made up of representatives from all countries that have signed the United Nations Framework Convention on Climate Change (UNFCCC). At these meetings, countries come together to negotiate agreements and set goals for reducing greenhouse gas emissions and addressing the impacts of climate change.

Copernicus

Copernicus is the Earth observation component of the European Union’s Space programme. It provides accurate, timely and easily accessible information to improve the management of the environment, understand and mitigate the effects of climate change and ensure civil security. ESA coordinates the delivery of data from upwards of 30 satellites. The European Commission, acting on behalf of the European Union, is responsible for the overall initiative, setting requirements and managing the services.

Copernicus Contributing Missions

The Copernicus Contributing Missions provide data that complements the Copernicus Sentinel missions and play a crucial role in Earth observation. These missions are conducted by ESA, its Member States, and international third-party operators, and they offer high-resolution optical and radar data.

Copernicus Data Space Ecosystem

The Copernicus Data Space Ecosystem provides access to large amounts of open and free Earth observation data.

Copernicus Sentinels

The Copernicus Sentinels are a series of Earth observation satellites developed as part of the European Union's space programme. These satellites are equipped with advanced sensors and instruments to monitor Earth's environment, providing a wealth of data for various applications, including environmental management, climate monitoring and disaster response.

Copernicus Sentinel Expansion Missions

Copernicus Sentinel Expansion missions will expand the current capabilities of the Copernicus Space Component – the world’s biggest supplier of Earth observation data. These missions are being developed by ESA on behalf of the EU.

CRISTAL

The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) mission will provide a full picture of the changes taking place in some of the most inhospitable regions of the world. It will carry – for the first time – a dual-frequency radar altimeter, and microwave radiometer, that will measure and monitor sea-ice thickness, overlying snow depth and ice-sheet elevations.

These data will support maritime operations in the polar oceans and contribute to a better understanding of climate processes. CRISTAL will also support applications related to coastal and inland waters, as well as providing observations of ocean topography. CRISTAL is one of six Copernicus Sentinel Expansion missions that ESA is developing on behalf of the EU. 

CryoSat

Launched on 8 April 2010, the CryoSat mission is monitoring centimetre-scale changes in the thickness of ice floating in the oceans and in the thickness of the vast ice sheets that blanket Greenland and Antarctica. Together with satellite information on ice extent, these measurements are showing how the volume of Earth's ice is changing and leading to a better understanding of the relationship between ice and climate.

Cryosphere

The cryosphere is one of the components of Earth’s system where water is in solid form, encompassing regions with ice, snow and frozen ground. This includes polar ice caps, glaciers, ice sheets, sea ice, and frozen lakes and rivers. The cryosphere is dynamic, experiencing changes in response to seasonal variations and long-term climate shifts. Monitoring changes in the cryosphere is crucial for understanding the impacts of climate change and its broader environmental consequences.

D 

Data

Data refers to information, often in the form of facts, figures, or symbols, that is collected, stored, and analysed.

Data cube

A data cube is a simple a way of organising and viewing any sort of data with multiple dimensions, some of which are associated with space and time, that can help gain insights into patterns and trends that might not be immediately apparent otherwise.

Data set

A data set is a collection of related and organised information or data points that are grouped together for analysis or reference.

Deforestation

Deforestation is the process of clearing or removing large expanses of forests or trees, often to make way for agriculture, urban development or other land-use changes. This human-induced activity results in the loss of forest ecosystems, disrupting biodiversity, contributing to climate change by reducing the carbon sink capacity of forests, and impacting local and global ecosystems. Deforestation can have significant environmental consequences, including soil erosion, altered water cycles, and the destruction of habitats for numerous plant and animal species.

Degradation

Degradation refers to the deterioration or decline in the quality, condition, or functionality of something. For environmental degradation, it refers to where natural resources or ecosystems experience a decline in health or integrity. Degradation may result from factors such as pollution, deforestation, overuse of land, or other human-induced and natural processes. Rainforest degradation results in the loss of biodiversity, disruption of ecological balance, and diminished capacity to provide essential ecosystem services.

Delta

A delta is a landform that forms at the mouth of a river where the river flows into a larger body of water, such as a sea or an ocean. Deltas are usually triangular or fan-shaped and are formed over a long period of time as sediment, such as sand, silt, and clay, is deposited at the mouth of the river.

Deltas can be very productive ecosystems, as they are often home to a variety of plant and animal species, and the sediment that is deposited can make the soil fertile for agriculture. They can also be vulnerable to flooding and erosion, as they are often located at low elevations and can be affected by storm surges and sea level rise.

Desertification

Desertification is the process of which fertile lands becomes desert. It involves the gradual transformation of productive land into desert-like conditions, characterised by reduced soil fertility, vegetation loss, and increased susceptibility to erosion. Factors contributing to desertification include prolonged droughts, deforestation, overgrazing and improper agricultural practices.

Destination Earth

Destination Earth (DestinE) is an ambitious initiative of the European Union to create a digital model of Earth that will be used to monitor the effects of natural and human activity on our planet, anticipate extreme events and adapt policies to climate-related challenges.

Using innovative Earth system models, cutting-edge computing, satellite data and machine learning, Destination Earth will allow its users to explore the effects of climate change on the different components of the Earth system, together with possible adaptation and mitigation strategies.

Digital elevation model

A digital elevation model (DEM) is a digital representation of the topography of a terrain or surface.

Digital twin

A digital twin is a virtual representation or digital replica of a physical object, system, or process. It integrates real-time data and simulations to mimic the behaviour, characteristics and dynamics of its physical counterpart.

DLR

German Aerospace Center.

Dobson Unit

A Dobson Unit (DU) is a unit of measurement that is used to express the total amount of ozone in a vertical column of the Earth's atmosphere.

Doppler effect

The Doppler effect is a phenomenon observed in waves, such as sound or light, when the source of the waves and the observer are in relative motion. It causes a change in the frequency or wavelength of the waves as perceived by the observer.

Doppler radar

Doppler radar is a type of radar system that utilises the Doppler effect to measure the velocity of moving objects, such as precipitation particles in the atmosphere.

Downwelling

The process of accumulation and sinking of warm surface waters along a coastline.

Drought

Drought is a prolonged period of abnormally low precipitation levels, resulting in water shortages that can adversely affect ecosystems, agriculture and water supplies. 

E 

EarthCARE

The Earth Cloud Aerosol and Radiation Explorer (EarthCARE) mission is a European-Japanese mission to improve the representation and understanding of Earth's radiative balance in climate and numerical weather forecast models.

Earth Explorers

Earth Explorers refer to a series of satellite missions with the primary goal of advancing scientific understanding of Earth's environment, climate and natural processes. These missions, which are proposed by the scientific community, continue to demonstrate how breakthrough technology can deliver an astounding range of scientific findings about our planet.

They lead to the scientific excellence that is critical to addressing the challenges society faces today and is expected to face in the decades to come – from understanding different aspects in the climate system such as atmospheric dynamics and ice melt, to societal issues such as food security and freshwater resources.

Earth observation

Earth observation refers to the collection, analysis and interpretation of information about Earth's surface, atmosphere, and oceans using various technologies such as satellites, aircraft, and ground-based sensors.

Earth system

The Earth system encompasses the interconnected and dynamic interactions among the atmosphere, hydrosphere (water bodies), lithosphere (land), biosphere (living organisms), and sometimes the cryosphere (frozen components). This holistic approach views Earth as a complex, integrated system where processes and feedback mechanisms between these components influence the planet's climate, weather patterns, and environmental conditions.

Earth system science

Earth system science explores the interactions and relationships among Earth's various components, including the atmosphere, hydrosphere, lithosphere, biosphere and the cryosphere. It aims to understand the complex dynamics and processes that govern Earth as a whole. Earth system scientists analyse how changes in one component can impact others, contributing to a holistic understanding of the planet's functioning. This integrated approach helps address environmental challenges, such as climate change, by considering the interconnected nature of Earth's systems.

Ecology

Ecology is the study of the relationships between living organisms, including humans and their physical environment.

Ecosystem

An ecosystem is a biological community of living organisms, including plants, animals, and microorganisms, interacting with each other and their physical environment in a specific area.

ECMWF

European Centre for Medium-Range Weather Forecasts.

ECSAT

ECSAT stands for the European Centre for Space Applications and Telecommunications. It is one of ESA’s establishments located in Harwell, United Kingdom. ECSAT focuses on the application of space technologies for various purposes, including telecommunications, Earth observation and satellite navigation.

El Niño

El Niño is a climate phenomenon characterised by the periodic warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean. This warming disrupts normal weather patterns, leading to significant climatic impacts globally.

El Niño events typically occur every two to seven years and can bring about extreme weather conditions. In most years, the warming last only a few weeks or a month, after which the weather patterns return to normal and fishing improves. However, when El Niño conditions last for many months, more extensive ocean warming occurs and economic results can be disastrous. El Niño has been linked to wetter, colder winters in the United States; drier, hotter summers in South America and Europe; and drought in Africa.

This phenomenon is part of the larger El Niño-Southern Oscillation (ENSO) climate system and has widespread effects on ecosystems, agriculture, and weather-related disasters in various regions across the world.

Electromagnetic radiation

Electromagnetic radiation refers to the energy propagated through space in the form of electromagnetic waves. These waves consist of electric and magnetic fields oscillating perpendicular to each other and perpendicular to the direction of the wave's propagation.

Electromagnetic spectrum

The electromagnetic spectrum refers to the entire range of electromagnetic radiation, organised by wavelength or frequency. It includes various types of electromagnetic waves, such as radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. Each segment of the spectrum represents a different range of wavelengths and has distinct properties and interactions with matter.

Electromagnetic wave

An electromagnetic wave is a form of energy propagation through space that consists of oscillating electric and magnetic fields perpendicular to each other and perpendicular to the direction of the wave's travel.

Elliptical orbit

Bodies in space orbit in elliptical rather than circular orbits because of factors such as gravity and atmospheric drag. The point where the orbiting satellite is closest to Earth is called the perigee while the point where the satellite is farthest from Earth is called the apogee.

El Niño-Southern Oscillation (ENSO)

El Niño-Southern Oscillation (ENSO) is a climate phenomenon characterised by the periodic variations in sea surface temperatures and atmospheric pressure patterns in the equatorial Pacific Ocean. ENSO has two phases: El Niño, marked by warmer-than-average sea surface temperatures, and La Niña, characterised by cooler-than-average sea surface temperatures. These variations influence global weather patterns, impacting precipitation, temperature and atmospheric circulation in different regions. ENSO events can lead to extreme weather conditions, such as droughts, floods, and altered storm patterns, with widespread consequences for agriculture, ecosystems, and various socio-economic activities around the world.

Environment

The air, water and land in or on which people, animals and plants live.

Envisat

Envisat was the largest Earth observation spacecraft ever built. The mission delivered thousands of images and a wealth of data used to study the workings of the Earth system, including insights into factors contributing to climate change. The end of the mission was declared on 9 May 2012, but ten years of Envisat’s archived data continue to be exploited for studying our planet.

ERS

The European Remote Sensing satellites (ERS) were the most sophisticated Earth observation spacecraft ever developed and launched by Europe. The satellites collected a wealth of valuable data on Earth’s land surfaces, oceans and polar caps and were called upon to monitor natural disasters such as severe flooding or earthquakes in remote parts of the world.

Both ERS satellites were built with a core payload of two specialised radars and an infrared imaging sensor. The two were designed as identical twins with one important difference: ERS-2 included an extra instrument to monitor ozone levels in the atmosphere.

ESA

European Space Agency

ESOC

ESOC stands for the European Space Operations Centre. It is one of ESA’s main located in Darmstadt, Germany. ESOC is responsible for the operations and control of ESA's spacecraft and satellites throughout their mission lifecycles.

ESRIN

ESRIN stands for the European Space Research Institute and is one of ESA’s centres for Earth observation activities. ESRIN is located in Frascati, Italy, near Rome and was established in 1966.

The mission and payload operations of ESA’s Earth observation satellites are managed in ESRIN. It is the primary source for the acquisition, distribution and exploitation of data from these and other non-ESA satellites.

Essential climate change variables (ECVs)

Essential Climate Variables (ECVs) are a set of key climate parameters that are systematically observed to provide information on various aspects of the Earth's climate system. They are crucial for understanding climate change, assessing its impacts, and informing climate-related policies.

ESTEC

ESTEC stands for the European Space Research and Technology Centre. It is ESA’s largest establishment and is located in Noordwijk, the Netherlands. ESTEC serves as the agency's primary facility for research and development, focusing on space technology and satellite missions.

Estuary

An estuary is a partially enclosed coastal body of water where fresh water from rivers and streams mixes with salt water from the ocean. Estuaries are usually located where a river meets the sea, and they are influenced by tides, waves, and currents. Because of the mixing of fresh and salt water, estuaries are highly productive ecosystems that support a wide variety of plant and animal life.

Eumetsat

European Organisation for the Exploitation of Meteorological Satellites

Eutrophication

Eutrophication is a natural process that occurs when a body of water becomes enriched with nutrients such as nitrogen and phosphorus. While this can be a normal part of the ecosystem, excessive levels of nutrients from human activities like agriculture, sewage and stormwater runoff can lead to an overgrowth of algae and other aquatic plants. As these plants die and decompose, they consume oxygen, which can lead to hypoxia (low oxygen levels) and harm aquatic life. Eutrophication can also cause harmful algal blooms that produce toxins that can be harmful to people, animals and the environment.

Evaporation

Change from a liquid (more dense) to a vapour or gas (less dense) form.

F 

False-colour

False-colour refers to the presentation of data using colours that do not represent the natural colours of the observed objects. Instead, false-colour images use artificial colour schemes to highlight specific features or information that may not be apparent in standard true-colour images. Different bands of the electromagnetic spectrum, such as infrared or ultraviolet, are often assigned specific colours to enhance the visibility of certain characteristics, such as vegetation health or land cover.

Feedback mechanisms

In the context of climate, feedback mechanisms refer to processes that can either amplify or dampen the effects of climate change. Positive feedback loops tend to intensify initial changes, potentially accelerating warming or cooling trends. An example is the ice-albedo feedback, where melting ice reduces surface reflectivity, leading to more absorption of sunlight and further warming. Negative feedback loops, on the other hand, work to stabilise the climate system. An example is the water vapour feedback, where warmer temperatures increase water vapour in the atmosphere, but this can also lead to increased cloud cover, which reflects sunlight and helps cool the planet.

FLEX

The Fluorescence Explorer (FLEX) will map vegetation fluorescence to quantify photosynthetic activity. This information will improve our understanding of the way carbon moves between plants and the atmosphere and how photosynthesis affects the carbon and water cycles. It will also lead to better insight into plant health and stress.

Fluorocarbons

Carbon-fluorine compounds that often contain other elements such as hydrogen, chlorine or bromine.

FORUM

The Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission will provide new insight into the planet’s radiation budget and how it is controlled, and therefore improve climate models. More than half of Earth’s outgoing longwave energy is in the far-infrared part of the electromagnetic spectrum, which has not been measured. FORUM will fill this gap.

Fossil

Hardened remains or traces of animal or plant life from a previous geological period preserved in Earth’s crust.

Fossil fuel

Fossil fuels are natural energy resources derived from the remains of ancient living organisms that underwent geological processes over millions of years. The three primary types of fossil fuels are coal, oil (petroleum) and natural gas.

Fraction of Absorbed Photosynthetically Active Radiation (FAPAR)

Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) is the fraction of photosynthetically active radiation (PAR) absorbed by a vegetation canopy.

FutureEO

FutureEO is ESA’s Earth observation research and development programme. It harnesses novel ideas to develop pioneering satellite missions and concepts, nurturing imaginative new ways of using Earth observation that enables scientific excellence to flourish and address environmental challenges of tomorrow.

Earth science is at the heart of this forward-looking programme, but FutureEO, critically, also underpins the development of operational satellite missions dedicated to delivering robust systematic data for services that improve daily life and boost the economy. The agility of FutureEO also offers room for manoeuvre, with provision to adapt to emerging challenges and opportunities for daring new observing ideas to be tested, opening the door even wider to innovation.

G 

Geoid

The geoid is the surface of an ideal global ocean in the absence of tides and currents, shaped only by gravity. It is a crucial reference for measuring ocean circulation, sea-level change and ice dynamics – all affected by climate change.

Geostationary

Geostationary refers to a satellite that is orbiting Earth at the same rate as Earth's rotation, which allows it to appear stationary in the sky relative to a fixed point on Earth's surface. This is achieved by placing the satellite in a very specific orbit approximately 35,786 km above Earth's equator, where it can complete one orbit in the same amount of time it takes for the Earth to rotate once on its axis (about 24 hours).  Geostationary satellites are commonly used for weather forecasting, communication, and navigation, as they provide continuous coverage over a fixed region of Earth's surface.

Glacier

A glacier is a large, persistent mass of ice that forms from the accumulation, compaction and recrystallisation of snow over long periods. Glaciers move slowly under their own weight, shaping the landscape through processes like erosion and deposition. They are found in mountainous regions and polar areas and play a crucial role in Earth's hydrological cycle, influencing sea level and contributing to the formation of characteristic glacial landforms.

Global carbon budget

The global carbon budget refers to the balance of carbon dioxide emissions and removals on a global scale over a specific period, typically a year. It accounts for the total amount of carbon dioxide released into the atmosphere through human activities such as burning fossil fuels and deforestation, as well as the natural processes that absorb or sequester carbon, like photosynthesis and carbon storage in oceans and forests.

Global warming

Global warming refers to the long-term increase in Earth's average surface temperature, primarily attributed to human activities, such as the burning of fossil fuels and deforestation. The enhanced greenhouse effect, caused by the accumulation of greenhouse gases like carbon dioxide in the atmosphere, traps more heat, leading to a rise in global temperatures. This warming has far-reaching consequences, including changes in weather patterns, rising sea levels and impacts on ecosystems.

GOCE

Launched on 17 March 2009 and ended on 11 November 2013, the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission provided the data to accurately determine global and regional models of Earth's gravity and geoid. This is advancing research in areas of ocean circulation, physics of Earth's interior, geodesy and surveying, and sea-level change. 

Gravity

Gravity is the fundamental force of attraction between objects with mass. It pulls objects toward each other and gives weight to physical bodies. The strength of gravity is proportional to the mass of the objects and inversely proportional to the square of the distance between their centres.

Greenhouse effect

The greenhouse effect is a natural process that warms Earth's surface. It occurs when the Sun's energy reaches Earth and is absorbed, then re-radiated as infrared radiation. Greenhouse gases in Earth's atmosphere, such as carbon dioxide, water vapour and methane, trap some of this outgoing infrared radiation, preventing it from escaping into space. This trapped heat warms the planet, creating conditions suitable for life. However, human activities, particularly the burning of fossil fuels, have increased the concentration of greenhouse gases, enhancing the natural greenhouse effect and contributing to global warming and climate change.

Greenhouse gas

Greenhouse gases are gases in Earth's atmosphere that can trap heat, contributing to the greenhouse effect and influencing the planet's temperature. The primary greenhouse gases include carbon dioxide, methane, nitrous oxide, water vapour and fluorinated gases. Human activities, such as burning fossil fuels, deforestation and industrial processes, have increased the concentrations of these gases, enhancing the greenhouse effect and leading to global warming and climate change.

Guano

Guano is excrement produced specifically from bats and seabirds.

H 

Habitat

The area or region where a type of plant or animal lives and grows.

Harmony

The Harmony mission will deliver a wide range of unique high-resolution observations of motion occurring at or near Earth’s surface. New information about our oceans, ice, earthquakes and volcanoes will make significant contributions to climate research and risk monitoring.

Heat island effect

The heat island effect, often referred to as the urban heat island effect, is a phenomenon where urban areas experience higher temperatures compared to their surrounding rural areas. This temperature difference is primarily attributed to human activities, such as the construction of buildings and roads, the replacement of natural surfaces with heat-absorbing materials, and the concentration of heat-producing activities. Urban heat islands can lead to elevated temperatures, altered microclimates, increased energy consumption for cooling, and potential environmental and health impacts. Mitigation measures often focus on urban planning, green infrastructure and sustainable design to counteract the heat island effect.

Hemisphere

Half of Earth, usually as divided into northern and southern halves by the equator, or into western and eastern halves by an imaginary line passing through the poles.

Hydrocarbon

Hydrocarbons are organic compounds made up of hydrogen and carbon atoms. They form the basis of fossil fuels, such as coal, oil and natural gas, and can also be found in various organic substances. Hydrocarbons exist in different forms, including alkanes, alkenes, and alkynes, each characterised by the arrangement of carbon atoms and the presence of carbon-carbon double or triple bonds. These compounds play a crucial role in the energy industry as sources of fuel and raw materials for various industrial processes.

Hydrochlorofluorocarbon

Hydrochlorofluorocarbons are organic compounds that consist of hydrogen, chlorine, fluorine and carbon atoms. They were developed as substitutes for chlorofluorocarbons which are known for their ozone-depleting properties. While hydrochlorofluorocarbons have lower ozone-depleting potential than chlorofluorocarbons, they still contribute to ozone layer depletion. Due to their environmental impact, international agreements such as the Montreal Protocol aim to phase out the production and consumption of hydrochlorofluorocarbons.

HydroGNSS

The Earth observation Scout mission, HydroGNSS, will improve our knowledge of Earth’s hydrological cycle, and in turn, improve our understanding of natural processes and the way human activity affects land and water.

It will provide measurements of key hydrological climate variables, including soil moisture, freeze–thaw state over permafrost, inundation and wetlands, and above-ground biomass, using a technique called Global Navigation Satellite System (GNSS) reflectometry.

Hydrologic cycle

The hydrologic cycle, also known as the water cycle, is the continuous process of water movement on, above, and below Earth's surface. It involves the evaporation of water from oceans, lakes and rivers into the atmosphere, condensation into clouds, precipitation as rain or snow, and the return of water to Earth through runoff or infiltration. The hydrologic cycle plays a fundamental role in distributing and replenishing Earth's water resources, sustaining ecosystems and influencing weather patterns. It is a dynamic system driven by solar energy and operates on a global scale, connecting various components of the Earth's environment.

Hydrosphere

A hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground and in the air. A planet's hydrosphere can be liquid, vapour or ice. On Earth, liquid water exists on the surface in the form of oceans, lakes and rivers.

Hyperspectral

Hyperspectral refers to an imaging or sensing system that captures a broad range of wavelengths across the electromagnetic spectrum with high spectral resolution. Unlike standard imaging systems that record colours in three or four bands, hyperspectral systems capture numerous narrow and contiguous bands, providing detailed information about the spectral characteristics of the observed objects.

I 

Ice core

Ice cores are cylinders of ice drilled from ice sheets and glaciers which can be used to study climate patterns of the past.

Ice sheet

An ice sheet is a massive, continuous expanse of glacial ice covering more than 50 sq km. These vast ice masses are found predominantly in polar regions, with Antarctica and Greenland being the two primary locations hosting Earth's largest ice sheets. Ice sheets form over extended periods as accumulated snow compacts into ice, creating layers that can reach great thicknesses.

Ice shelf

An ice shelf is a floating, extended portion of a glacier or ice sheet that extends into the ocean but remains connected to the land. Unlike icebergs, which are detached pieces of ice, ice shelves are still anchored to coastal areas or continental landmasses. They form as glacial ice flows from land into the ocean and subsequently floats due to buoyancy. Notable ice shelves include the Ross Ice Shelf in Antarctica and the Filchner-Ronne Ice Shelf.

InCubed

InCubed is a co-funding programme that supports the development of innovative and commercially successful products and services in Earth observation. InCubed encourages high-risk/high-reward developments by mitigating technical and financial risks.

Imager

A satellite instrument that measures and maps Earth and its atmosphere.

In situ

In situ is a Latin term that means ‘in its original place’ or ‘on-site.’ In scientific and technical contexts, the term is often used to describe measurements or observations that are made directly in the natural environment, rather than in a laboratory or other controlled setting. For example, conducting in situ measurements of soil moisture or water quality involves taking measurements in the field, at the location of interest.

Infrared radiation

Infrared radiation is a type of electromagnetic radiation with wavelengths longer than those of visible light but shorter than microwaves. It is characterised by its ability to transmit heat and is commonly associated with thermal energy. In the Earth's atmosphere, certain gases, such as water vapour and carbon dioxide, can absorb and re-emit infrared radiation, contributing to the greenhouse effect and influencing the planet's climate.

Interferogram

An interferogram is a graphical representation or image created through interferometry, a technique that analyses the interference patterns between waves. In the context of radar interferometry, such as interferometric synthetic aperture radar, an interferogram displays the phase differences between two or more radar signals acquired at different times. These phase differences represent ground displacement, allowing scientists to visualize and quantify changes in Earth's surface, such as those caused by earthquakes, subsidence or other geological phenomena.

Interferometry

Interferometry is a technique that involves combining and analysing the interference patterns of waves to extract detailed information about the properties of the waves or the objects that emitted them.

In the context of earthquakes, interferometry refers to a technique known as interferometric synthetic aperture radar. This uses satellite-based radar systems to measure ground deformation caused by seismic activity. By comparing the phase differences in radar signals acquired at different times, scientists can create detailed maps of surface displacement, identifying areas that have moved due to an earthquake.

International Charter Space and Major Disasters

The International Charter on Space and Major Disasters, commonly known as ‘the Charter,’ is an international collaboration that provides rapid and coordinated access to space-based Earth observation data for disaster response and recovery efforts.

IPCC

Intergovernmental Panel on Climate Change

Isothermal

Of or indicating equality of temperature.

J 

JAXA

Japan Aerospace Exploration Agency.

Jet stream

The jet stream is a fast, narrow current of air flowing from west to east that encircles the globe.

K 

Kelvin

The standard unit of thermodynamic temperature which is defined as 1/273.16 of the temperature of the triple point of water above absolute zero. The symbol for Kelvin is K.

Kyoto Protocol

The Kyoto Protocol is an international treaty aimed at addressing global climate change by setting legally binding emissions reduction targets for developed countries. Adopted in 1997 in Kyoto, Japan, under the United Nations Framework Convention on Climate Change (UNFCCC), the protocol commits participating nations to limit or reduce their greenhouse gas emissions, primarily carbon dioxide, methane and nitrous oxide. The Kyoto Protocol came into force in 2005 and played a significant role in shaping subsequent climate agreements and discussions.

L 

La Niña

La Niña is a climate phenomenon characterised by the periodic cooling of sea surface temperatures in the central and eastern equatorial Pacific Ocean. It is the opposite phase of the El Niño-Southern Oscillation (ENSO) cycle compared to El Niño.

During La Niña events, the cooler-than-average sea surface temperatures influence atmospheric circulation patterns, leading to distinct climatic effects globally. These effects may include increased rainfall in some regions, droughts in others, and alterations in temperature and weather patterns.

Lahar

A lahar is a type of mudflow or debris flow composed of volcanic ash, rocks and water that occurs on or around a volcano. Lahars can be triggered by heavy rainfall, rapid snowmelt, or the melting of glaciers on the volcano's slopes, which mixes with loose volcanic material such as ash and rocks.

Lake

A body of fresh or salt water surrounded by land.

Land cover

Land cover refers to the physical and biological characteristics of Earth's surface, as observed and categorised from satellite or aerial imagery. Land cover classification includes identifying and mapping different types of surfaces, such as forests, urban areas, water bodies, agricultural fields and natural landscapes. This information is crucial for monitoring changes in land use, assessing environmental impact and understanding ecosystems.

Land surface temperature

Land surface temperature is the temperature of Earth’s surface, how hot the ‘surface’ of Earth feels to the touch. This is not to be confused with air temperature which is a measure of how hot the air is above the ground.

Latitude

Latitude is a coordinate that specifies the north–south position of a point on the surface of Earth or another celestial body.

Leaf area index

Leaf area index is a measure used in ecology and remote sensing to quantify the extent of leaf cover in a vegetation canopy. It represents the total one-sided area of leaves per unit ground area.

LEO

Low Earth Orbit.

LEOP

Launch and Early Orbit Phase.

Lidar

Lidar, short for light detection and ranging, is a remote sensing technology that uses laser light to measure distances and create detailed, three-dimensional representations of Earth's surface or other objects. In a lidar system, laser pulses are emitted and the time it takes for the light to travel to the target and back is measured. This information is used to generate highly accurate and precise elevation models, topographic maps and other spatial data.

Lightning

The occurrence of a natural electrical discharge of very short duration and high voltage between a cloud and the ground or within a cloud.

Lithosphere

The component of Earth's surface comprising the rock, soil and sediments.

Longitude

The angular distance from the Greenwich meridian (0 degree), along the equator.

Low pressure system

A low pressure system is an atmospheric area where the atmospheric pressure at sea level is lower than the surrounding areas. In a low pressure system, air converges at the surface, ascends and creates conditions that are often associated with unsettled weather, such as clouds, precipitation and sometimes storms.

Low pressure systems play a crucial role in Earth's weather patterns, influencing the movement of air masses and the development of weather systems. Cyclones and hurricanes are extreme examples of low-pressure systems, characterised by intense winds and heavy rainfall.

LSTM

The Copernicus Land Surface Temperature Monitoring, LSTM, mission will improve sustainable agricultural productivity in a world of increasing water scarcity and variability.

The mission will carry a high spatial-temporal resolution thermal infrared sensor to provide observations of land-surface temperature.

These data are key to understand and respond to climate variability, manage water resources for agricultural production, predict droughts and also to address land degradation. LSTM is one of six Copernicus Sentinel Expansion missions that ESA is developing on behalf of the EU. 

M 

Magnetometer

A magnetometer is a scientific instrument used to measure the strength and direction of a magnetic field. It can detect the presence of magnetic fields, including those generated by natural sources like the Earth's magnetic field or artificial sources like magnets or electronic devices.

Magnetosphere

The magnetosphere is the region of space surrounding a celestial body, such as Earth, that is influenced and shaped by its magnetic field. Earth's magnetosphere is created by the interaction between the planet's magnetic field and the solar wind, a continuous flow of charged particles (mostly electrons and protons) emitted by the Sun.

Mass balance

The term ‘mass balance’ is often used by glaciologists to describe the difference between all the ice that is added to a glacier, and all of the ice the glacier loses over a period of time. The mass balance of a glacier considers factors such as snow accumulation, ice melt and ice flow. A positive mass balance indicates net mass gain, while a negative mass balance suggests net mass loss.

Mean sea level

Mean sea level is the average level of the surface of one or more of Earth's oceans over a specific period, usually a year. It serves as a reference point for measuring elevations and depths on Earth. Mean sea level is determined by taking into account variations caused by tides, atmospheric pressure and ocean currents.

Medicane

A medicane is a meteorological term used to describe a weather phenomenon known as a 'Mediterranean hurricane.' It refers to a tropical-like cyclone that forms over the Mediterranean Sea, exhibiting characteristics similar to hurricanes or typhoons but on a smaller scale.

Mesosphere

The part of Earth’s atmosphere between the stratosphere and the thermosphere in which temperature decreases with altitude.

Meteorology

Study of Earth’s atmosphere and its phenomena.

Meteosat

Europe’s series of Meteosat satellites has been improving the accuracy of weather forecasts for over 40 years. The first Meteosat was launched in 1977 and also goes down in history as ESA’s first Earth observation mission. From geostationary orbit, the Meteosat satellites provide a continuous stream of images of the whole Earth disc, to monitor the weather over Europe, Africa and parts of the Atlantic and Indian Ocean.

Meteosat Third Generation (MTG)

The Meteosat Third Generation is a series of geostationary meteorological satellites envisioned as a successor to the Meteosat First and Second Generation satellites.

The third generation of weather satellites will not only guarantee the continuity of data for weather forecasting for the next two decades, but also offers significant enhancement of the current imager capabilities, an all-new infrared sounding capability and realtime lightning imaging for early detection  of severe storms as they develop.

Methane

Methane is a colourless, odourless, and flammable gas that is the primary component of natural gas. Methane is produced naturally through biological and geological processes, including the decomposition of organic matter and fossil fuel formation. It is a potent greenhouse gas, with a global warming potential around 25 times greater than carbon dioxide over a 100-year time frame. Methane plays a significant role in both natural and human-caused climate change, and reducing methane emissions is an important strategy for mitigating the impacts of climate change.

MetOp

MetOp is a series of polar-orbiting meteorological satellites. The MetOp programme aims to enhance global weather forecasting, climate monitoring and environmental research by providing accurate and timely observations of the Earth's atmosphere, oceans and land surfaces. The programme was jointly established by ESA and the European Organisation for the Exploitation of Meteorological Satellites (Eumetsat), forming the space segment of Eumetsat's Polar System (EPS).

Montreal Protocol

The Montreal Protocol is an international treaty designed to protect Earth's ozone layer by phasing out the production and consumption of substances that deplete it, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and other ozone-depleting substances (ODSs). The treaty was signed in 1987 and has been ratified by all United Nations member countries.

Multi-temporal

Multi-temporal imaging is an application of remote sensing that involves taking two or more satellite images and combining them. This process highlights changes between the images over different dates.

N 

NanoMagSat

NanoMagSat aims to maintain Europe’s leadership in monitoring Earth’s magnetic field and will also measure the ionospheric environment. NanoMagSat will allow for a much-improved understanding of the dynamics of the magnetic field and of the role of the Sun in the coupled atmospheric–ionospheric–magnetospheric system.

Information delivered by NanoMagSat will be used in many ways, such as for space weather hazard assessments, precise navigation, reference models for smart phones, directional drilling and in the World Magnetic Model.

NASA

National Aeronautics and Space Administration

Near infrared

Near infrared refers to the region of the electromagnetic spectrum with wavelengths just beyond the visible light spectrum, typically ranging from approximately 700 to 2500 nanometres. While human eyes cannot detect NIR radiation, certain sensors and instruments, including those used in remote sensing and spectroscopy, are designed to capture and analyse information within this wavelength range.

Negative feedback

An interaction that reduces or dampens the response of the system in which it is incorporated.

Net primary production

Net primary production is a measure of the amount of organic matter, primarily in the form of plant biomass, that is produced by photosynthetic organisms in an ecosystem. It represents the difference between the total amount of energy captured through photosynthesis and the energy expended by the organisms during cellular respiration.

In other words, it is the net gain of energy or biomass available for consumption by herbivores and other organisms within an ecosystem. It is a key indicator of the productivity and health of an ecosystem, reflecting the energy available for higher trophic levels and for supporting various ecological processes.

Net zero

Net zero emissions refer to the state in which the total amount of greenhouse gases emitted into the atmosphere is balanced by an equivalent amount of greenhouse gases removed or offset. Achieving net zero involves reducing emissions through various measures, such as transitioning to renewable energy sources and improving energy efficiency, while also actively removing or offsetting remaining emissions. This concept is crucial in the context of addressing climate change, aiming to minimise the overall impact of human activities on Earth's climate system.

New Space

New Space is a revolution in the commercialisation of space activities, enabling both new and established enterprises, including start-ups, Small and medium-sized enterprises (SMEs) and large companies, to access space directly. The market has attracted a great deal of private investment, and in Earth observation many private satellites have been launched to provide remote sensing data for customers.

Nitrogen dioxide

Nitrogen dioxide is a reddish-brown gas and one of the nitrogen oxides, a group of air pollutants. It forms when nitrogen oxides produced during combustion processes, such as those in vehicles and industrial facilities, react with the atmosphere. Sources of nitrogen dioxide include motor vehicle emissions, power plants and certain industrial activities.

In the atmosphere, nitrogen dioxide can contribute to air pollution and have adverse effects on human health. It is a key component of smog and can irritate the respiratory system, leading to respiratory problems, particularly in individuals with pre-existing conditions. Nitrogen dioxide also plays a role in the formation of acid rain and contributes to the formation of fine particulate matter, which can have environmental and health impacts. Monitoring and controlling nitrogen dioxide emissions are important for air quality management and public health.

Nitrogen oxides

Nitrogen oxides are a group of reactive gases that contain nitrogen and oxygen atoms. The two main nitrogen oxides are nitrogen monoxide and nitrogen dioxide. Nitrogen oxides are produced through combustion processes, particularly in vehicles, power plants, industrial facilities and wildfires, where high temperatures cause nitrogen and oxygen in the air to react.

In the atmosphere, nitrogen oxides can have various environmental and health impacts. It contributes to the formation of ground-level ozone and fine particulate matter, both of which can have detrimental effects on air quality and human health. Nitrogen oxide emissions also play a role in the nitrogen cycle and can lead to acid rain, affecting ecosystems and water quality.

Nitrous oxide

Nitrous oxide is a colourless and odourless gas composed of nitrogen and oxygen. It is a greenhouse gas with a variety of sources, both natural and human-induced. Nitrous oxide is naturally produced in soil through microbial processes, and it is released into the atmosphere through activities such as agricultural practices, industrial processes and the combustion of fossil fuels.

While nitrous oxide makes up a relatively small portion of the Earth's greenhouse gases, it is potent in terms of its ability to trap heat in the atmosphere. It plays a role in the greenhouse effect, contributing to global warming and climate change. Additionally, nitrous oxide is involved in the depletion of the ozone layer.

NOAA

National Oceanic and Atmospheric Administration

Normalised Difference Vegetation Index

The Normalised Difference Vegetation Index (NDVI) is a numerical indicator used in remote sensing to assess the health and abundance of vegetation cover on Earth's surface. NDVI is calculated based on the reflectance of electromagnetic radiation in the red and near-infrared regions of the spectrum.

NDVI is widely used in agriculture, forestry and environmental monitoring to assess vegetation conditions, monitor changes over time and provide valuable insights into land cover and ecosystem health.

North Atlantic Oscillation

The North Atlantic Oscillation is a climate phenomenon characterised by the variation of atmospheric pressure differences between the Icelandic Low (a low-pressure area near Iceland) and the Azores High (a high-pressure area near the Azores).

O 

Ocean

An ocean is a large body of saltwater that covers more than 70% of the Earth's surface. There are five major oceans: the Atlantic Ocean, the Pacific Ocean, the Indian Ocean, the Southern Ocean, and the Arctic Ocean. Oceans support a diverse array of marine life and play a crucial role in regulating Earth's climate and weather patterns.

Ocean colour

Ocean colour is the hue or shade of blue, green or brown that is visible on the surface of the ocean. The colour of the ocean is affected by a number of factors, including the depth of the water, the amount of sunlight that penetrates the surface and the presence of microscopic plant-like organisms called phytoplankton. For example, chlorophyll and other pigments of phytoplankton can colour the water bright blue or green, while sediments can turn the water milky blue or brown.

Orbit

Orbit refers to the curved path that an object, such as a planet, satellite or moon, follows around another celestial body, typically due to gravitational attraction.

Satellite orbits are the designated paths that artificial satellites follow around celestial bodies, typically Earth. These orbits are carefully chosen based on the specific mission objectives and requirements of the satellite.

Satellites can occupy various types of orbits, such as low Earth orbit (LEO), medium Earth orbit (MEO), and geostationary orbit (GEO). Low Earth orbits are closer to Earth's surface and are often used for Earth observation and communication satellites, providing relatively short orbital periods. Medium Earth orbits are positioned at intermediate altitudes and are commonly used for navigation satellites like those in the Global Positioning System (GPS).

Geostationary orbits are located directly above the equator, allowing satellites to match Earth's rotation and appear stationary relative to a fixed point on the ground, making them ideal for communication and weather satellites. Each orbit type offers distinct advantages depending on the satellite's purpose and intended coverage area.

Ozone

Ozone is a gas that is naturally present in Earth's atmosphere. It is formed when oxygen molecules are split apart by ultraviolet radiation from the sun and recombine with other oxygen molecules. Ozone is concentrated in a layer called the ozone layer, located in the stratosphere.

The ozone layer plays a critical role in protecting life on Earth by absorbing most of the sun's harmful ultraviolet (UV) radiation, which can cause skin cancer, cataracts and other health problems in humans and animals. However, in the late 20th century, scientists discovered that certain human-made chemicals, such as chlorofluorocarbons (CFCs), were destroying the ozone layer. This led to the signing of the Montreal Protocol in 1987, an international agreement to phase out the production and use of ozone-depleting substances.

Today, the ozone layer is slowly recovering as a result of the Montreal Protocol and other international efforts. However, the process is expected to take several decades, and there is ongoing research to better understand the dynamics of the ozone layer and the impact of human activities on its recovery.

Ozone hole

The ozone hole is a region of severely depleted ozone in Earth's stratosphere over the Antarctic. It is caused by the release of human-made chemicals, such as chlorofluorocarbons (CFCs), which break down in the upper atmosphere and release chlorine and other compounds that destroy ozone molecules. Ozone is important because it absorbs harmful ultraviolet radiation from the sun, which can cause skin cancer, cataracts, and other health problems in humans and other animals, as well as damage crops and other vegetation. The depletion of the ozone layer over Antarctica was first detected in the 1980s, and it has since become an important environmental issue. While the ozone hole is still present, it has been slowly recovering since the phase-out of ozone-depleting substances under the Montreal Protocol.

Ozone layer

The ozone layer is a natural layer of gas in Earth's atmosphere that helps to protect the planet from harmful ultraviolet radiation from the Sun. It is mainly located in the stratosphere, between 15 and 30 km above Earth, and is composed of ozone molecules. The ozone layer is crucial for life on Earth, as prolonged exposure to UV radiation can cause skin cancer, cataracts, and other health problems in humans and animals. However, the ozone layer has been threatened by the release of human-made chemicals such as chlorofluorocarbons (CFCs), which can break down the ozone molecules. Efforts to reduce the production and use of CFCs have helped to slow down the depletion of the ozone layer, but it is still important to continue to monitor and protect it.

Ozone mini hole

The term ‘ozone mini hole’ typically refers to a localised and temporary reduction in the concentration of ozone in Earth's stratosphere. Unlike the more widely recognised Antarctic ozone hole, which occurs annually over the Southern Hemisphere, ozone mini holes are smaller and less pronounced events that may occur in other regions or during different seasons.

Ozone mini holes are often associated with specific atmospheric conditions that contribute to the depletion of ozone, such as the presence of polar stratospheric clouds and variations in temperature and sunlight. While they are not as severe or persistent as the Antarctic ozone hole, these mini holes can still have implications for regional ozone levels and may be influenced by factors like human-made ozone-depleting substances.

P 

Paleoclimate

Climate as it existed in the distant past, before historical records.

Paris Agreement

The Paris Agreement is an international treaty established within the United Nations Framework Convention on Climate Change (UNFCCC). Adopted in December 2015 during the 21st Conference of the Parties (COP 21) in Paris, the agreement outlines global efforts to combat climate change and limit global warming.

Particulates

Particulates, also known as particulate matter (PM), refer to tiny particles or droplets in the air that can be solid or liquid. These particles vary in size and composition and can originate from natural sources, such as wildfires, dust storms, and volcanic eruptions, as well as human activities like industrial processes, transportation, and combustion of fossil fuels.

Particulates are categorized based on their size, with PM10 representing particles with diameters of 10 micrometres or smaller and PM2.5 referring to even smaller particles with diameters of 2.5 micrometres or smaller. These fine particles can have significant impacts on air quality and human health as they can penetrate deep into the respiratory system when inhaled.

Parts per billion

Parts per billion (ppb) is a unit of measurement used to express the concentration of a substance in a mixture, solution, or the atmosphere. One part per billion is equivalent to one part of a substance for every billion parts of the total mixture. It is a very small unit of measurement, indicating a proportionally tiny amount.

Payload

Instruments that are accommodated on a spacecraft.

Permafrost

Permafrost is a layer of soil, sediment, or rock that remains at or below freezing temperatures for two or more consecutive years. It is typically found in Arctic and sub-Arctic regions, where the ground is covered by snow and ice for much of the year. Permafrost is important because it stores large amounts of carbon and other greenhouse gases, as well as other organic matter and minerals. When permafrost thaws, it can release these stored materials into the atmosphere, amplifying global warming and climate change. Thawing permafrost can also cause the ground to become unstable, leading to land subsidence, landslides, and other hazards.

Phi (ɸ)

The ancient Greek letter ɸ (pronounced as ‘Phi’) symbolises harmony and a co-existence of different elements into one single entity. In science, besides the famous 'golden ratio', it also represents things that are in a state of flux as well as the momentum wave function in quantum physics.

Phi-lab (ɸ-lab)

ESA’s Φ-lab is an open innovation laboratory that acts as a hub and catalyst for Earth observation transformative ideas. Φ-lab aims to strengthen the world-leading competitiveness of the European Earth observation industrial and scientific sectors.

Phi-Sat-1 (ɸ-sat-1)

ɸ-sat-1, pronounced phisat-1, is artificial intelligence technology carried on one of the two CubeSats that make up the Federated Satellite Systems mission (FSSCat). Its hyperspectral camera images in the visible, near-infrared and thermal-infrared parts of the electromagnetic spectrum and acquires an enormous number of images of Earth.

The ɸ-sat-1 artificial intelligence chip filters out less than perfect images image of Earth so that only usable data are returned. This makes the process of handling all these data more efficient, allowing users access to more timely information.

Phi-Sat-2 (ɸsat-2)

Φsat-2 is a miniature satellite – a cubesat – designed to demonstrate how different Artificial Intelligence technologies can advance observing Earth from space. As well as carrying a multispectral imager, Φsat-2’s Artificial Intelligence applications will, for example, eliminate images that are cloudy, detect and classify maritime vessels and transform images into street maps for disaster response.

Photosynthesis

Photosynthesis is the biological process by which green plants, algae and certain bacteria convert light energy into chemical energy in the form of glucose or other sugars. This process takes place in the chloroplasts of plant cells, specifically in the green pigment called chlorophyll.

In simple terms, carbon dioxide and water, in the presence of sunlight, are converted into glucose and oxygen. The glucose produced serves as an energy source for the plant and is essential for its growth and development. Meanwhile, the release of oxygen into the atmosphere during photosynthesis is a critical component of Earth's oxygen cycle and supports the respiration of animals and other organisms.

Phytoplankton

Phytoplankton are microscopic, plant-like organisms that live in aquatic environments, including oceans, lakes, and rivers. They are the base of the marine food chain, converting energy from the Sun into organic matter through photosynthesis. Phytoplankton are important producers of oxygen and play a crucial role in regulating Earth's climate by absorbing carbon dioxide from the atmosphere.

Pixel

A pixel, derived from ‘picture element’, represents the ground area which corresponds to the smallest unit of a digital image dataset.

Polarimetry

Polarimetry is a method of measuring and interpreting polarised waves, such as electromagnetic or visible light. This enables the analysis of an object or location. 

Polar orbit

A polar orbit is a specific type of satellite or spacecraft orbit that passes over or nearly over Earth's polar regions. In a polar orbit, the satellite travels from pole to pole, or vice versa, as it orbits Earth.

Polar vortex

The polar vortex is a large area of low pressure and cold air that is typically centred near Earth's poles, particularly over the Arctic region. It is a natural and persistent atmospheric circulation pattern that forms during the winter months.

Occasionally, disruptions or weakening of the polar vortex can lead to the southward movement of frigid air masses, causing outbreaks of extremely cold temperatures in mid-latitude regions. These cold air outbreaks are often associated with severe winter weather, including snowstorms and freezing conditions.

Pollutant

A pollutant is a substance or agent introduced into the environment that has harmful or undesirable effects on living organisms, ecosystems or the environment as a whole.

Common pollutants include air pollutants such as carbon monoxide, sulphur dioxide, and particulate matter, as well as water pollutants like chemical contaminants and microbial agents. Pollutants can have adverse effects on air quality, water quality, soil health and the overall balance of ecosystems.

Positive feedback

An interaction that amplifies the response of the system in which it is incorporated.

PPM

PPM stands for 'parts per million' which is a way of expressing the concentration of one component in the larger sample. Climate scientists and activists use the term to describe the concentration of pollutants, like carbon dioxide or methane, in the atmosphere. 

Proba-1

Proba-1, Project for On-Board Autonomy is a small Earth observation satellite developed by ESA. It is part of the Proba (PRoject for On-Board Autonomy) series, which aims to demonstrate advanced spacecraft and instrument technologies.

Proba-V

Proba-V is a small Earth observation satellite developed by ESA. Launched on May 7, 2013, Proba-V is part of the Proba (PRoject for On-Board Autonomy) series, which focuses on demonstrating innovative technologies and conducting Earth observation missions. The ‘v’ in Proba-V stands for vegetation.

Primary productivity

Primary productivity refers to the rate at which primary producers, such as plants, algae and certain bacteria, convert solar energy into organic compounds through the process of photosynthesis. It represents the synthesis of organic matter, usually in the form of carbohydrates, from inorganic substances like carbon dioxide and water.

Primary productivity is a critical component of ecosystems as it forms the basis of the food chain. The organisms that perform photosynthesis create a source of energy and nutrients for the entire ecosystem. The total amount of organic matter produced in a given area over a specific time period is a measure of the primary productivity of that ecosystem.

There are two main types of primary productivity: gross primary productivity (GPP), which represents the total energy captured by producers, and net primary productivity (NPP), which accounts for the energy used by the producers in respiration.

Q 

Quantum computing

An experimental form of computing that uses multiple quantum states to perform calculations, potentially achieving much faster results than a classical computer. The basic unit of information in quantum computing is the qubit.

Quantum Computing for Earth Observation (QI4EO) 

Quantum Computing for Earth Observation (QI4EO) draws on the power of quantum computers and quantum machine learning to improve performance, decrease computational costs and solve previously intractable problems in Earth observation information processing and analysis.

R 

R&D

Research and development

Radar interferometry

The study of interference patterns caused by radar signals.

Radiation

Radiation is the emission or transmission of energy in the form of electromagnetic waves or particles that release energy when absorbed by an object.

Radiation budget

The radiation budget refers to the balance between incoming and outgoing radiation in Earth's atmosphere. It is a key concept in understanding the energy exchanges between Earth and space. Earth receives energy from the Sun, primarily in the form of shortwave solar radiation. This incoming solar radiation is partly reflected back to space by clouds, atmospheric particles, and Earth's surface, and the rest is absorbed.

On the other hand, Earth emits energy as longwave infrared radiation. This outgoing infrared radiation is influenced by factors such as Earth's surface temperature, atmospheric composition and cloud cover. The radiation budget is considered balanced when the incoming solar radiation equals the outgoing infrared radiation.

Rainforest

A rainforest is a dense and lush forest ecosystem characterised by high annual precipitation, high humidity and a rich diversity of plant and animal life. These forests are typically found in tropical regions near the equator, where the climate is warm and wet throughout the year. Rainforests are vital contributors to global biodiversity, housing a wide variety of species, many of which are unique to these ecosystems.

Real time

As it happens.

Reflection

The return of light or sound waves from a surface.

Remote sensing

Remote sensing refers to the process of collecting information about objects, areas or phenomena from a distance, typically using sensors or instruments that are not in direct physical contact with the target. This technology allows the observation, measurement and monitoring of Earth's surface, atmosphere and oceans from aircraft or satellites.

Remote sensing instruments can capture various types of data, including imagery, spectrometry and radar signals. These data are then analysed to gather information about land cover, vegetation health, climate patterns, atmospheric composition and other environmental factors.

Applications of remote sensing are diverse and include environmental monitoring, agriculture, forestry, urban planning, disaster management, and climate studies. Remote sensing provides a valuable tool for scientists, researchers and policymakers to acquire large-scale, accurate and up-to-date information about Earth's features and processes.

ROSE-L

The Copernicus Radar Observation System for Europe in L-band (ROSE-L) will provide continuous day-and-night all-weather monitoring of Earth’s land, oceans and ice, and offer frequent observations of Earth’s surface at a high spatial resolution.

ROSE-L will carry an active phased array synthetic aperture radar instrument. The radar antenna will be the largest deployable planar antenna ever built measuring an impressive 40 sq m.

ROSE-L will deliver many benefits including essential information on forests and land cover, leading to improved monitoring of the terrestrial carbon cycle and carbon accounting.

The mission will also greatly extend our ability to monitor minute surface displacements and helping detect geohazards. It will automatically map surface soil moisture conditions over land helping improve hydrology and weather forecasts and support the operational monitoring of sea and land ice across the Arctic. ROSE-L is one of six Copernicus Sentinel Expansion missions that ESA is developing on behalf of the EU. 

Runoff

Runoff refers to the movement of water, usually from precipitation, across the land surface. When rain, snowmelt, or other forms of precipitation occur, the water does not always get absorbed by the soil. Instead, it may flow over the land surface, forming streams, rivers or eventually reaching larger bodies of water like lakes or oceans.

The amount of runoff is influenced by various factors, including the type of soil, land cover, slope of the terrain and the intensity and duration of precipitation. Impermeable surfaces like pavement and urban areas can increase runoff, as water is less able to infiltrate the ground.

Runoff plays a significant role in Earth's hydrological cycle and can have implications for water availability, erosion, flooding and the transport of nutrients and pollutants. Understanding runoff is crucial for managing water resources and mitigating the impacts of extreme weather events.

S 

Salinity

Salinity is a measure of the saltiness or salt content of a body of water.

Scattering

Scattering, in a general sense, refers to the process of redirecting the path of light, sound, or other waves as they encounter particles, obstacles, or irregularities in a medium. This phenomenon occurs when waves interact with objects that are smaller than their wavelength. The direction and intensity of the waves may change due to scattering.

In the context of light, scattering plays a crucial role in various natural phenomena. In atmospheric science, scattering is fundamental to understanding the behaviour of electromagnetic waves, such as in remote sensing or the dispersion of sunlight.

Scatterometer

A scatterometer is a radar designed for the measurement of ground or sea reflectivity.

Science for Society

Through its Science for Society activities, ESA’s Earth observation programme forges new scientific discoveries and pioneers new services, stimulating downstream industrial and economic growth. These activities drive the development of a network of Earth observation exploitation platforms in Europe to foster easier and more comprehensive exploitation of the data.

Scouts

Scout missions are a new component of ESA’s Earth Observation FutureEO programme. This family of small satellites delivers value-added science, either by demonstrating new observing techniques in space or by miniaturising existing space technologies. A Scout mission is defined by three key aspects: it must deliver innovative science and technology, it must cost less than €30 million (€35 million pending approval) and it must be developed within three years, from kick-off to launch.

Sea-ice thickness

Sea-ice thickness refers to the measurement of the vertical dimension of ice floating on the ocean surface. It is a crucial parameter in understanding the state and dynamics of sea ice, which plays a significant role in Earth's climate system.

Sea-ice thickness can vary widely, ranging from a thin layer of newly formed ice to multi-year ice that has survived multiple melt seasons. The thickness of sea ice is influenced by factors such as freezing and melting processes, atmospheric conditions and oceanic heat flux.

Sea level

Sea level refers to the average level of the surface of the world's oceans. It serves as a baseline reference point for measuring elevation and depth on Earth.

Sea-surface temperature (SST)

The average temperature of water close to the ocean’s surface.

Sensor

A sensor refers to a specialised instrument or device that is designed to collect data from space and Earth's atmosphere. These sensors are equipped on satellites for various purposes, including Earth observation, environmental monitoring and scientific research.

Satellite sensors can be classified into different types based on the kind of data they collect. Some common satellite sensors include optical sensors which capture images of Earth's surface using visible and infrared light. They are used for applications like land cover mapping, agriculture monitoring and urban planning.

Radar sensors use radio waves to detect and measure the properties of the Earth's surface. They are useful for all-weather and day-and-night imaging, making them valuable for applications such as topography mapping and monitoring changes in land surfaces.

Thermal infrared sensors measure the infrared radiation emitted by Earth's surface, providing information about temperature variations. They are used in applications like climate studies, thermal mapping and identifying heat sources.

Sentinel-1

Sentinel-1 is a polar-orbiting, all-weather, day-and-night radar imaging mission for land and ocean services.

Sentinel-2

Sentinel-2 is a polar-orbiting, multispectral high-resolution imaging mission for land monitoring to provide, for example, imagery of vegetation, soil and water cover, inland waterways and coastal areas.

Sentinel-3

Sentinel-3 is a multi-instrument mission to measure sea-surface topography, sea- and land-surface temperature, ocean colour and land colour with high-end accuracy and reliability.

Sentinel-4

Part of the Copernicus Atmosphere Monitoring Service (CAMS), Sentinel-4 focuses on monitoring atmospheric composition over Europe.

Sentinel-5

Part of the Copernicus Atmosphere Monitoring Service (CAMS), Sentinel-5 monitors global atmospheric composition, including key pollutants and greenhouse gases.

Sentinel-5P

Sentinel-5 Precursor – also known as Sentinel-5P – is the first Copernicus mission dedicated to monitoring our atmosphere. The satellite carries the state-of-the-art Tropomi instrument to map a multitude of trace gases, which affect air quality and climate.

Sentinel-6

Sentinel-6 carries a radar altimeter to measure global sea-surface height, primarily for operational oceanography and for climate studies.

Seosat-Ingenio

SEOSAT-Ingenio – Spanish for ingenuity – was designed to image Earth’s land with a resolution of 2.5 m. With its capability to look sideways, it could have accessed any point on Earth within three days. The mission would have benefitted society through numerous disciplines such as cartography, agriculture, forestry, urban development and water management.

SMOS

ESA's Soil Moisture and Ocean Salinity (SMOS) mission is making global observations of soil moisture and ocean salinity. By consistently mapping these two variables, SMOS is advancing our understanding of the exchange processes between Earth's surface and atmosphere and helping to improve weather and climate models.

Soil moisture

Soil moisture refers to the amount of water content present in the soil. It represents the proportion of water relative to the total volume of soil, typically expressed as a percentage. Monitoring soil moisture from space involves measuring the water content in the top layer of the soil, which plays a crucial role in various environmental processes.

Soil sealing

Soil sealing refers to the process whereby soil surfaces are covered by impermeable materials such as concrete, asphalt or buildings, preventing water from infiltrating into the ground. This usually occurs in urban and industrial areas because of construction, car parks and other forms of development.

When soil is sealed, it loses its ability to absorb rainwater, leading to increased surface runoff and reduced groundwater recharge. This can contribute to various environmental problems, including flooding, soil erosion, loss of biodiversity and decreased soil fertility. Soil sealing also exacerbates the urban heat island effect by reducing the cooling effect of soil evaporation and vegetation.

Solar flare

A solar flare is a tremendous explosion on the Sun that happens when energy stored in 'twisted' magnetic fields (usually above sunspots) is suddenly released. In a matter of just a few minutes they heat material to many millions of degrees and produce a burst of radiation across the electromagnetic spectrum, from radio waves to X-rays and gamma rays.

Scientists classify solar flares according to their peak brightness in X-ray wavelengths. There are five categories, listed here in order from most intense to least intense:

X-class flares are the biggest; they are major events that can trigger radio blackouts around the whole world and long-lasting radiation storms in the upper atmosphere.

M-class flares are medium-sized; they generally cause brief radio blackouts that affect Earth's polar regions. Minor radiation storms sometimes follow an M-class flare.

C-class flares are small with few noticeable consequences here on Earth. At its peak, a C-class flare is ten times less powerful than an M-class flare.

B-class flares are ten times smaller or weaker than C-class flares.

A-class flares are at least ten times less intense than B-class flares, with no noticeable consequences on Earth.

To indicate the strength of a flare, the class letter is often followed by a number. The higher the number, the stronger the flare.

Solar maximum

The point in the solar cycle at which sunspot activity is highest.

Solar minimum

The point in the solar cycle at which sunspot activity is lowest.

Solar radiation

Solar radiation refers to the energy received from the Sun, primarily in the form of visible light, infrared radiation and ultraviolet radiation. This radiant energy is a fundamental source of heat and light for Earth, driving various atmospheric and surface processes.

Sounder

A specialised type of radiometer designed to gauge variations in atmospheric temperature at different altitudes.

Southern oscillation

The Southern oscillation refers to a climate phenomenon characterised by the periodic, seesaw-like changes in atmospheric pressure patterns between the eastern and western tropical Pacific Ocean. It is a part of the larger El Niño-Southern Oscillation (ENSO) climate system.

During the Southern Oscillation's positive phase, known as La Niña, the eastern tropical Pacific experiences cooler-than-average sea surface temperatures, leading to higher-than-normal atmospheric pressure. In contrast, the negative phase, known as El Niño, involves warmer-than-average sea surface temperatures in the eastern tropical Pacific, accompanied by lower-than-normal atmospheric pressure.

These phases of the Southern Oscillation have widespread effects on global weather patterns, influencing rainfall, temperature and atmospheric circulation. La Niña tends to be associated with increased rainfall in some regions and drought in others, while El Niño can bring about opposite effects, such as reduced rainfall in normally wet areas and increased precipitation in typically arid regions.

Space for a Green Future Accelerator

ESA’s Space for a Green Future Accelerator responds to the global climate and environmental crisis, in support to a sustainable Green Transition towards a carbon-neutral, resource-efficient and resilient society. It will stimulate the development, deployment and use of advanced data, science, technology, applications and services for a sustainable life on Earth.

The accelerator will deliver actionable information, assessing scenarios for policy implementation and tailored services for European decisionmakers to reach carbon neutrality by 2050 and establish global leadership in the competition for the rapidly emerging green economy. In doing do, it will also contribute to the European social and economic well-being, minimising the socio-environmental impacts caused by climate change.

Spatial

Refers to a location, size or area of something.

Spatial resolution

Spatial resolution refers to distance between independent measurements, or the physical dimension that represents a pixel of the image.

Spectral band

Spectral bands are different ranges of wavelengths of light that are captured by a satellite sensor.

Stratosphere

The stratosphere is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere.

Subduction

Subduction is a geological process that occurs at the boundary between two tectonic plates, where one plate moves beneath the other and sinks into Earth's mantle. This occurs because the denser oceanic plate is pulled down by gravity into the hotter and more fluid mantle beneath the less dense continental plate. As the oceanic plate descends, it causes earthquakes and creates magma that rises to the surface, leading to volcanic activity. Subduction is responsible for the formation of many of the Earth's mountain ranges, such as the Andes in South America, the Cascades in North America and the Japanese Alps.

Subsidence

Subsidence is the sinking of Earth's surface, often caused by natural or human-induced factors. Natural subsidence can occur due to geological processes such as the compaction of sediments, the collapse of underground caverns or sinkholes, or the natural settling of wetlands. Human-induced subsidence is often caused by activities such as groundwater extraction, mining, and the construction of buildings and infrastructure.

Subsidence can have serious consequences, including damage to buildings and infrastructure, increased risk of flooding, and the loss of land and ecosystems. In coastal areas, subsidence can exacerbate the effects of sea level rise, increasing the risk of coastal erosion and flooding.

Sulphur dioxide

Sulphur dioxide is a colourless gas composed of one sulphur atom and two oxygen atoms. It is produced by the combustion of fossil fuels containing sulphur and various industrial processes. Sulphur dioxide is a major air pollutant, contributing to respiratory issues in high concentrations.

Sun-synchronous

Sun-synchronous refers to a specific type of orbit used by Earth observation satellites that enables them to pass over any given point on Earth's surface at the same local solar time during each orbit. In a sun-synchronous orbit, the satellite maintains a consistent angle between its orbital plane and the Sun, which results in a fixed illumination angle for the observed area.

This orbit is designed to optimise the acquisition of consistent and uniform lighting conditions across successive satellite passes, facilitating better comparison of images and data collected over time. Sun-synchronous orbits are commonly used in applications such as Earth observation, remote sensing and environmental monitoring, where consistent lighting conditions are essential for accurate data interpretation and analysis.

Sunglint

Sunglint refers to the phenomenon where sunlight is reflected directly back towards an observer on Earth's surface from a water body, creating a bright, mirror-like reflection.

This effect occurs when the angle between the incoming sunlight, the water surface and the observer is favourable for the reflection. Sunglint can be observed in satellite images and photographs, and it often appears as a shimmering or glinting area on the water's surface, making it challenging to discern features beneath the reflection. Scientists and satellite observers take sunglint into account when interpreting and analysing Earth observation data.

Sunspot

A region on the surface of the Sun that is temporarily cool and dark compared to surrounding areas.

Sustainable Development Goals (SDGs)

The Sustainable Development Goals (SDGs) are a set of 17 global goals established by the United Nations in 2015 as part of the 2030 Agenda for Sustainable Development. The SDGs are designed to address a range of interconnected social, economic and environmental challenges facing the world. They provide a comprehensive framework for countries, organisations and individuals to work collectively towards a more sustainable and equitable future.

SWARM

Swarm is a constellation of three satellites to measure precisely the magnetic signals that stem from the magnetosphere, ionosphere, Earth's core, mantle, crust and the oceans. This sampling, in both space and time, will lead to an improved understanding of the processes that drive Earth's 'dynamo', which appears to be weakening.

Swath

The area observed by a satellite as it orbits Earth.

Synoptic view

The ability to see large areas at the same time.

Synthetic aperture radar (SAR)

Synthetic Aperture Radar (SAR) is a remote sensing technology that uses radar to create high-resolution images of Earth's surface. Unlike optical remote sensing techniques that rely on visible or infrared light, SAR works by transmitting radio waves towards Earth's surface and measuring the reflection of the waves.

SAR is capable of imaging Earth's surface regardless of cloud cover, darkness or weather conditions. It is used for a wide range of applications, including mapping and monitoring of terrain, detecting changes in land use, measuring ocean currents and wave heights, and monitoring natural disasters such as floods and earthquakes. SAR has many civilian applications in fields such as agriculture, forestry and environmental monitoring.

T 

Tango

The Tango mission will measure and monitor three greenhouse gases: methane, carbon dioxide and nitrogen dioxide being emitted from large industrial sites. Tango will monitor 150–300 known large industrial facilities and power plants every four days.

It will deliver high-resolution images of emission plumes as well as the surrounding pollution, with sufficient accuracy to determine emissions with a single observation. In fact, Tango will deliver higher-resolution images at these specific locations compared to the other three missions noted above provide, so therefore acts as a magnifying glass.

Telemetry

The process of recording and transmitting the readings of an instrument.

Temperature

Temperature is a measure of the degree of hotness or coldness of an object or substance, reflecting the average kinetic energy of its particles. It is typically measured using scales such as Celsius, Fahrenheit, or Kelvin and plays a fundamental role in determining the thermal state of matter, influencing physical properties and heat transfer processes.

Temporal

Refers to frequency of data acquisition.

Terminus (glacier)

The end of a glacier.

Thermal

Relating to heat.

Thermosphere

The thermosphere is the uppermost layer of Earth's atmosphere, located between the mesosphere and the exosphere. It is a region of extremely low density, where the few remaining molecules are mostly oxygen and nitrogen. Despite its low density, the thermosphere is extremely hot, with temperatures that can reach over 1000°C due to the absorption of high-energy solar radiation. The thermosphere is also the site of many important natural phenomena, including the auroras, which are caused by charged particles from the Sun interacting with Earth's magnetic field. The thermosphere is also home to satellites that orbit Earth, including the International Space Station.

Third Party Missions

The Third Party Missions (TPM) programme has been operating for over 45 years and consists of a series of satellites specifically focused on Earth observation which are owned by commercial and public organisations worldwide.

Thunder

Thunder is the sound produced by the rapid expansion of air surrounding a lightning bolt during a thunderstorm. It is a result of the intense heating of the air by the electrical discharge of lightning, causing the air to rapidly expand and create a shockwave. Thunder is often heard as a loud, rumbling noise and is a natural phenomenon associated with atmospheric electrical activity.

Topography

Topography refers to the physical and detailed mapping of the surface features of a region, including its natural and human-made features such as mountains, valleys, rivers, lakes, roads and buildings. It involves the representation of the variations in elevation and terrain relief, providing a three-dimensional description of Earth's surface.

Trace gas

A trace gas is a gaseous component in Earth's atmosphere that makes up only a small fraction of the overall composition. Despite its low concentration, trace gases play significant roles in atmospheric processes and climate dynamics. Examples of trace gases include greenhouse gases like carbon dioxide, methane and ozone, as well as various pollutants and atmospheric constituents that may have important environmental and climatic implications.

Transpiration

The process of losing water through the surface or skin of a body or a plant.

Tropical

From or relating to the area between the two tropics.

Tropomi

The Tropospheric Monitoring Instrument (Tropomi) is a state-of-the-art spectrometer mounted on the Sentinel-5 Precursor satellite. Tropomi is designed to measure a wide range of atmospheric trace gases with high spatial resolution.

It provides crucial data on air quality, greenhouse gas concentrations, and other atmospheric components, contributing to the monitoring of environmental changes and supporting climate research.

Troposphere

The troposphere is the lowest layer of Earth's atmosphere, extending from the surface to an average altitude of about 8 to 15 km. It is where weather events occur and is characterised by a decrease in temperature with increasing altitude. The troposphere contains the majority of Earth's air mass and is crucial for supporting life and various meteorological phenomena.

It is where clouds form, and the majority of Earth's weather, including rain, snow, and storms, takes place. The boundary between the troposphere and the stratosphere, called the tropopause, marks the upper limit of this layer.

Tropospheric ozone

Ozone that is in the troposphere.

TRUTHS

The Traceable Radiometry Underpinning Terrestrial- and Helio-Studies, TRUTHS, mission will be a ‘standards laboratory in space’, setting the ‘gold standard’ reference for climate measurements. Carrying a cryogenic solar absolute radiometer and a hyperspectral imaging spectrometer as well as a novel onboard calibration system, TRUTHS will make continuous measurements of incoming solar radiation and reflected radiation to evaluate Earth’s energy-in to energy-out ratio.

Tundra

Tundra is a biome characterised by vast, treeless landscapes with low temperatures and a short growing season. Found primarily in the Arctic and subarctic regions, as well as some high-altitude mountain areas, tundra environments are dominated by low shrubs, grasses, mosses, and lichens. The soil is often frozen, a condition known as permafrost, which limits the depth of plant roots.

U 

Ultraviolet radiation

Ultraviolet (UV) radiation is a type of electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays. UV radiation is naturally present in sunlight and can also be artificially produced by certain types of lamps and lasers. While UV radiation has many beneficial effects, such as helping the human body produce vitamin D, it can also be harmful to human health. Exposure to too much UV radiation can cause skin damage, including sunburn and skin cancer, and can also damage the eyes. To protect against UV radiation, it is important to wear protective clothing, use sunscreen, and avoid direct exposure to sunlight during peak hours.

UNFCCC

United Nations Framework Convention on Climate Change.

Upwelling

Upwelling is an oceanographic phenomenon in which cold, nutrient-rich waters from thedeep ocean rise to the surface. This typically occurs along coastlines where prevailing winds push surface waters away, allowing the colder, nutrient-laden waters to well up and replace them. Upwelling is essential for marine ecosystems as it brings nutrients to the surface, supporting the growth of phytoplankton and initiating a cascade of biological productivity.

V 

Validation

Validation refers to the process of assessing the accuracy and reliability of the data collected by satellite or remote sensing instruments by comparing it with independent, ground-based measurements or established reference data. Validation is a critical step in ensuring the quality and trustworthiness of the information obtained from Earth observation systems.

W 

Water cycle

The water cycle, also known as the hydrological cycle, is a continuous and natural process through which water circulates within Earth's atmosphere and surface. It involves the phases of evaporation, condensation, precipitation, runoff and infiltration. Water is constantly evaporating from oceans, lakes and rivers into the atmosphere, where it forms clouds through condensation. The condensed water then falls back to Earth's surface as precipitation, including rain, snow, sleet or hail. This water can flow over the land surface as runoff, infiltrate into the ground, or be taken up by plants. The water cycle plays a crucial role in maintaining Earth's water balance, sustaining ecosystems and influencing climate patterns.

Water vapour

Water vapour is the gaseous form of water, existing in the atmosphere. It is the result of water undergoing the process of evaporation, where liquid water is transformed into vapor due to an increase in temperature. Water vapour is an essential component of the Earth's atmosphere and is involved in the water cycle, contributing to processes such as condensation, cloud formation, and precipitation. The amount of water vapour in the air can vary with temperature and atmospheric conditions, influencing weather patterns and humidity levels.

Wavelength

The distance between two waves of energy.

Weather

When you look outside your window on any given day, what you see is weather. Weather shows the way the atmosphere behaves and can change from minute-to-minute, hour-to-hour and day-to-day. There are many components to weather, which include temperature, rain, wind, hail, snow, humidity, flooding, thunderstorms, heatwaves and more.

WMO

World Meteorological Organization