Use of the Topex–Poseidon dual-frequency radar altimeter over land surfaces

Abstract

The capability of NASA radar altimeter Topex for land surface studies at regional or global scale is investigated. The analyzed data, available since mid-1992 consist of dual-frequency backscattering coefficients values (Ku and C band) estimated at the nadir pointing angle along the satellite tracks between 66°S and 66°N and averaged in 0.75° ground resolution cell. Mean global backscatter images of the entire land surfaces are presented in Ku, C band and the difference C–Ku. Statistics and major temporal signals over nine entire years are also presented at a global scale. Finally, temporal profiles of backscatters are extracted for main land types (desert, tropical forest, wet and dry savanna, boreal regions, ice sheet) to validate the dataset and to analyze radar response to land surface variability through 9 years. Results indicate the high capabilities of Topex–Poseidon (T–P) radar altimeter data for monitoring snow-covered regions at global and regional scale. The use of dual-frequency measurements can also improve methods developed with single frequency radar altimeter over complex vegetated areas. The complementarities for future synergy with wind-scatterometer or satellite imagery data over continents look also promising because of the T–P 10-day repeat cycle, a 10-year span dataset and a future better spatial resolution with combination of other dual-frequency altimetry missions such as ENVISAT or Jason.