The procedure for developing new Earth Explorer missions involves the science community from the very beginning. Through a peer-reviewed selection process, this on-going user-driven approach provides tools to further understand and monitor our planet.
A call for 'Core Earth Explorer Ideas' was released on 15 March 2005. The proposals were peer reviewed by scientific teams, and also appraised technically and programmatically. Based on these reviews, the Earth Science Advisory Committee (ESAC) evaluated the proposals and recommended a list of six mission ideas to the Director of Earth Observation Programmes. Following these recommendations, ESA’s Programme Board for Earth Observation approved the proposal to initiate Assessment Studies for six candidate missions.
With the Assessment Studies completed the six missions were presented to the science community and evaluated by the ESAC at a dedicated Earth Explorer User Consultation Meeting held in Lisbon, Portugal in January 2009:
The six candidate Earth Explorer missions were:
A-SCOPE - to improve our understanding of the global carbon cycle and regional carbon dioxide fluxes
The A-SCOPE mission concept aims to observe total column carbon dioxide with a nadir-looking pulsed Differential Absorption Lidar (DIAL). The lidar would have high-resolution ranging capability to provide additional information on tree canopy height. In addition, aerosol and cloud layer information could be gained as a spin-off. Contextual information would be acquired by an imaging instrument. The mission would realise a spatially-resolved global carbon budget combined with diagnostic model analysis through global and frequent observation of carbon dioxide.
BIOMASS - to take global measurements of forest biomass
The objective of the BIOMASS mission is to acquire global measurements of forest biomass to assess terrestrial carbon stocks and fluxes. The mission concept is envisaged as a novel spaceborne P-band synthetic aperture polarimetric radar operating at 435 MHz and a 6 MHz bandwidth. In addition to valuable data on forest biomass, the choice of radar sensor means that the mission could also provide new information on ice-sheet thickness and internal structures in cold regions, subsurface geology in arid regions, as well as data on soil moisture, permafrost and sea-surface salinity.
CoReH2O - to make detailed observations of key snow, ice and water cycle characteristics
The CoReH2O mission concept aims to fill the gaps in current information on snow, glaciers and surface water. The objective is to improve the modelling and prediction of water balance and streamflow for snow covered and glacierised basins, the modelling of water and energy cycles at high latitudes, and the forecasting of water supply from snow cover and glaciers, including the relation to climate change and variability. The mission concept employs twin frequency synthetic aperture radars (9.6 and 17.2 GHz) in two consecutive mission phases to deliver all-weather, year-round information on regional and continental-scale snow-water equivalent.
FLEX - to observe global photosynthesis through the measurement of fluorescence
The main aim of the FLEX concept is to make global observations of photosynthesis through the measurement of chlorophyll-fluorescence. Chlorophyll-fluorescence radiation is emitted from vegetation in the visible and infrared region of the electromagnetic spectrum and provides unique information about the photosynthetic activity of plants. FLEX will carry a very high-spectral resolution imaging spectrometer that allows the weak fluorescence signal to be decoupled from the reflected sunlight background. Secondary instruments will observe other variables such as vegetation temperature, which together with the fluorescence observations will allow for the assessment of light-use efficiency and exchange of carbon between plants and the atmosphere.
PREMIER - to understand atmospheric processes linking trace gases, radiation, chemistry and climate
The PREMIER concept aims to advance our understanding of the processes that link trace gases, radiation and chemistry in the upper troposphere and lower stratosphere. The radiative effects of water and clouds are at a maximum in this region. It is also a region characterised by small-scale processes that have not been studied by previous missions. The instrumentation will consist of an infrared limb-imaging spectrometer and a millimetre-wave limb-sounder. By linking with MetOp and the National Polar-orbiting Operational Environmental Satellite System (NPOESS) data, PREMIER also aims to provide insights into processes occurring in the lower troposphere.
TRAQ - to monitor air quality and long-range transport of air pollutants
The TRAQ mission concept focuses on air quality and the long-range transport of air pollutants. The objective is to understand more about the rate of air-quality change at regional and global scales, the strength and distribution of sources and sinks of tropospheric trace gases and aerosols influencing air quality, and the role of tropospheric composition in global change. A new synergistic sensor concept would allow for process studies, particularly with respect to aerosol-cloud interactions. The instrumentation concept consists of imaging spectrometers operating in ranges between ultraviolet and short-wave infrared, spectrometers in the thermal infrared, a multi-directional polarization imager and a cloud imager.
Based on recommendations by ESAC, ESA's Programme Board for Earth Observation selected BIOMASS, CoReH2O and PREMIER to go forward to Feasbility Study (Phase A).