Multiangle Backscattering Observations of Continental Surfaces in Ku-Band (13 GHz) From Satellites: Understanding the Signals, Particularly in Arid Regions
Résumé
Backscattering in Ku-band (13 GHz) over continen-
tal 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 (inci-
dence 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 scatter-
ings 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 ob-
servations at low and high incidence angles adds information,
particularly over desert surfaces.