"These two variables set the scene for a broad range of information we require. For example, we must know if there is anywhere we can't go due to steepness and roughness of terrain. Also, we need to know if there are any rivers to cross or infrastructure to avoid such as oil wells or pipelines whose activities may interfere with our signal." No single space-borne instrument can supply all the data required. Instead, data from a variety of different satellites are collected and combined within a geographic information system to yield information on accessibility, data quality, and source and receiver coupling.

The process begins with a digital elevation model, available from many sources including space shuttle mapping and ESA's ERS-tandem mission. This provides topographic and gradient information for logistics and safety planning. Next comes radar imagery from spacecraft such as Envisat and ERS to measure surface roughness, forming the basis of a map of coupling potential.

Visible light images provide infrastructure and land use information that help determine accessibility for vehicles and people. Also, surface vegetation detected in this imagery may indicate sediment-buried water channels that weaken signal propagation.

The ground reflects short-wave infrared (SWIR) light immediately, revealing the spectral characteristics of minerals at the surface. SWIR imagery, obtained from hyperspectral satellite sensors, is particularly sensitive to carbonates such as limestone and basalt and occurrences of softer materials such as gypsum or quartzite gravel.

Advancing further into the infrared spectra permits surveyors to peer deeper beneath the surface. Thermal infrared (TIR), or heat radiation from the surface, is a delayed response to incoming solar radiation,
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Contact: Mariangela D'Acunto
mariangela.d'acunto@esa.int
39-06-941-80-856
European Space Agency
28-Jan-2005