Multiangle Backscattering Observations of Continental Surfaces in Ku-Band (13 GHz) From Satellites: Understanding the Signals, Particularly in Arid Regions

Backscattering in Ku-band (13 GHz) over continental surfaces is analyzed, with the Tropical Rainfall Measurement Mission/Precipitation Radar instruments (incidence angles from 0° to 18°), along with observations from the Topex-Poseidon nadir-looking altimeter and the QuikSCAT scatterometer (incidence angles around 50°). The signals from the three instruments are very consistent. The backscattering tends to decrease with increasing vegetation density, as expected, making it possible to classify vegetation density with active microwaves. Over the northern African desert, a very large spatial variability of the backscattering is observed, with both surface and volume scatterings contributing to the signals. The use of multiangle observations does help characterizing the desert types, but in some areas, the ambiguity of the signals is still unexplained. The French-Chinese joint mission “Chinese-French Oceanic SATellite” will carry two active microwave instruments with a large range of incidence angles, from 0° to 50°. We show that the combined use of observations at low and high incidence angles adds information, particularly over desert surfaces.