Understanding vegetation response to climate variability from space: the scientific objectives, the approach and the concept of the SPECTRA mission

The goal of the SPECTRA mission is to improve the description of those processes by means of better constraints on and parameterizations of the associated models. The prime objective of SPECTRA is to determine the amount, assess the conditions and understand the response of terrestrial vegetation to climate variability and its role in the coupled cycles of energy, water and carbon. The amount and state of vegetation will be determined by the combination of observed vegetation properties and data assimilation. Specifically, the mission will characterize the amount and state of vegetation with observations of the following variables: (1) fractional vegetation cover; (2) Fraction Absorbed Photosynthetically Active Radiation (FAPAR); (3) albedo; (4) Leaf Area Index (LAI); (5) leaf chlorophyll content; (6) leaf water content; (7) foliage temperature; (8) soil temperature; (9) fractional cover of living and dead biomass. SPECTRA will provide spatially distributed observations (maps) of the key vegetation properties at the spatial resolution of one image pixel and a temporal frequency of one week or lower. Each map will cover an area of 50 km×50 km. The SPECTRA mission is being studied by the European Space Agency to address these scientific issues. The mission comprises the following elements: a space segment consisting of an imaging spectrometer covering the region 400 nm-2400 nm with a nominal spectral resolution of 10 nm and of an agile platform to perform subsequent, along track observations at seven view angles between -70° and +70°; a ground segment consisting of a core data processing facility and specialized Centers of Excellence to guarantee to a wide and diverse community access to higher level data products and to specialized data assimilation systems; and a field segment consisting of 50 to 100 dedicated sites where teams of investigators evaluate the observations and assimilate them in models describing the functioning of terrestrial ecosystems.