Earth Observation
In the framework of its Earth Observation Envelope Programme, the European Space Agency (ESA) carries out a number of different activities to support geophysical algorithm development, calibration/validation and the simulation of future space-borne earth observation missions. The general objectives of several existing and upcoming missions in the context of future EO programmes and their users is to provide a number of operational and also optional products, comprising atmospheric composition (Sentinel-5P, ADM-Aeolus, EarthCARE), operational data on rivers, deltas and marine hydrology (Sentinel 1), marine biogeochemistry and ecosystem (Sentinel 3A), monitoring and modelling subsurface geology, kinematics and dynamics of the Earth's crust, seismic and volcanic sources, geohazard assessment (EPOS, GEM), monitoring of changes to vegetation within the growing season (Sentinel 2A).
Starting from the supporting platforms, satellite instrumentation, Cal/Val technologies and tools, algorithms development, data storage, handling and distribution, up to service provision, Earth Observation includes all aspects, being therefore by definition a multidisciplinary field. All parts are inter-linked, contributing at different levels to a successful mission. Although being specialized on different structures of the Earth environment (atmosphere, water, land, vegetation) and different variables (wind, air composition, radiation, Earth's displacement, etc.), satellite missions have common problems (e.g. laser contamination), and generally rely on similar technologies (e.g. high spectral resolution lidars involved in ADM-Aeolus and EarthCARE), or mathematical algorithms (inverse problem in the retrieval of microphysical properties from optical parameters, atmospheric corrections).
Agriculture and Forestry
The Biomass mission will provide urgently needed measurements of forest biomass and forest height. The main satellite instrument is the first P-band synthetic aperture radar flown in space. The measurements will be used to generate global maps of forest biomass and forest height at a resolution of 200 m twice a year. In addition, the mission will have an experimental "tomographic" phase to provide 3D views of forests. The mission launch is envisaged to be around 2020.
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-2 can also deliver information for emergency services. Sentinel-2A was launched on June 23rd, 2015 and Sentinel-2B will follow in 2017. The nominal life of the mission is seven years. Sentinel-2 carries a high-resolution multispectral optical imager to monitor changes in vegetation. Data can be used to measure leaf area index, leaf chlorophyll and leaf water content to monitor plant growth, which is particularly important during the growing season, but also to generate land-cover maps, to track changes in the way land and to monitor the world's forests. In addition, Sentinel-2 provides information on pollution in lakes and coastal waters.
Urban Monitoring
Sentinel-1 is a polar-orbiting, all-weather, day-and-night radar imaging mission for land and ocean services. Sentinel-1A was launched on April 3rd, 2014 and Sentinel-1B on April 25th, 2016 with a nominal life of seven years. Carrying an advanced radar, Sentinel-1 images Earth's surface through rain and cloud regardless of whether or if it is day or night. Sentinel-1 offers information on wind and waves for safe passage, and can be used to track oil spills, as well as being used to generate timely maps of sea ice for ship routing. Routine images taken over land can be used for precision farming and to track land-use change. Offering insight into subsidence and uplift, Sentinel-1 is suited for urban planning and for monitoring volcanic activity.
Landslides & Earthquakes
SMOS - Soil Moisture and Ocean Salinity makes observations of soil moisture and ocean salinity. The mission was launched on November 2nd, 2009, with a nominal life of three years (including a six-month commissioning phase), extended to 2017. The SMOS satellite carries a novel interferometric radiometer that operates in the L-band microwave range to capture "brightness temperature" images. These images are used to derive global maps of soil moisture every three days, achieving an accuracy of 4% at a spatial resolution of about 50 km. Over land, SMOS is being used by the US Department of Agriculture to predict drought and by the European Centre for Medium-Range Weather Forecasts to help improve air temperature and humidity forecasts.
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. Swarm also aims to provide a better insight into Earth's crust and mantle. The mission was launched on November 22nd, 2013, with four years nominal life (including a six-month commissioning phase). The Swarm mission takes advantage of a new generation of magnetometers, enabling measurements to be taken over different regions of Earth simultaneously. In addition, Swarm data will be used to study the Sun's influence on Earth system by: analysing electric currents in magnetosphere and ionosphere; understanding the impact of solar wind on dynamics of the upper atmosphere.
Oceans, Seas, Lake and Rivers
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. The mission will support ocean forecasting systems, as well as environmental and climate monitoring. Sentinel-3A was launched on February 16th, 2016 with a nominal life of seven years (carries consumables for 12 years). Carrying a precision radar altimeter, an advanced infrared radiometer, and a wide-swath ocean and land imaging spectrometer, Sentinel-3 supplies a wealth of data related mainly to the marine environment. Additionally, ocean-colour data provide key information to monitor seawater quality and pollution. Applications using data acquired over land include re detection and land-cover mapping. Sentinel-3 also provides information to map the topography and extent of ice and to monitor the height of lake and river water.
Sentinel-6 carries a radar altimeter to measure global sea-surface height, primarily for operational oceanography and for climate studies. This information is essential for continued monitoring of changes in sea level, a key indicator of climate change. It is also essential for operational oceanography. Mapping up to 95% of Earth's ice-free ocean every 10 days, it offers vital information on ocean currents, wind speed and wave height for maritime safety. Sentinel-6 builds on heritage from the Jason series of ocean topography satellites and from ESA's CryoSat mission. Importantly, this new mission is designed to complement ocean information from Sentinel-3.
Air Quality
Sentinel-4 is a payload devoted to atmospheric monitoring that will be embarked upon a Meteosat Third Generation-Sounder (MTG-S) satellite in geostationary orbit. Sentinel-4 is an ultraviolet, visible and near-infrared spectrometer hosted on the Meteosat Third Generation Sounder satellite. From geostationary orbit, Sentinel-4 is providing information on a wide range of trace gases and pollutants, such as nitrogen dioxide and sulphur dioxide, this mission is essential for operational services relating to atmospheric composition. It also provides information on ozone and solar radiation for UV forecasting, and contributes to climate monitoring.
Sentinel-5 is a payload that will monitor the atmosphere from polar orbit aboard a MetOp Second Generation satellite. Sentinel-5 is an ultraviolet to shortwave infrared spectrometer carried on the MetOp Second Generation satellites. Taking advantage of synergies between the two missions, Sentinel-5 also uses data from MetOp Second Generation's thermal-infrared sounder and from two of its imagers. Complementing Sentinel-4, it provides wide-swath, global coverage data to monitor air quality around the world.
Sentinel-5 Precursor satellite mission is being developed to reduce data gaps between Envisat, in particular the Sciamachy instrument, and the launch of Sentinel-5. This mission will be dedicated to atmospheric monitoring. Sentinel-5 Precusor is the forerunner of Sentinel-5. It is a satellite carrying the Tropomi imaging spectrometer to provide timely information on a multitude of trace gases and aerosols affecting air quality and climate. Both Sentinel-5 and its predecessor are crucial for monitoring and tracking global air pollution, arming decision- makers with critical information to support policy making.
Climate Variables
CryoSat satellite 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. The mission was launched on April 8th, 2010, with a three-year minimum mission duration. CryoSat's primary instrument is a Synthetic Aperture Interferometric Radar Altimeter (SIRAL). It was designed to meet the measurement requirements for ice-sheet elevation and sea-ice freeboard, which is the height of ice protruding from the water. Reaching latitudes of 88°, CryoSat provides greater polar coverage than earlier missions.
Aeolus will be the first space mission to acquire profiles of the wind on a global scale. These near-real time observations will improve the accuracy of numerical weather and climate prediction, advancing our understanding of tropical dynamics and processes relevant to climate variability. The mission will be launch in 2017, with a nominal life of three years (including three-month commissioning phase). Aeolus carries an innovative Doppler wind lidar to probe the atmosphere and acquire global wind profiles up to an altitude of 30 km. Aeolus will pave the way for future operational missions to measure wind.
EarthCARE will advance our understanding of the role that clouds and aerosols play in reflecting incident solar radiation back into space and trapping infrared radiation emitted from Earth's surface. EarthCARE carries a high-spectral resolution atmospheric lidar, a radar instrument with Doppler measurement capability to provide cloud profiles, a multispectral imager and a broadband radiometer. The mission will acquire vertical profiles of clouds and aerosols, as well as the radiances at the top of the atmosphere to improve our understanding of Earth's radiative balance. These observations will lead to more reliable climate predictions and better weather forecasts. EarthCARE is scheduled for launch in 2018 with a design lifetime of three years, including a six-months commissioning phase.