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Spaceborne altimetry and scatterometry backscattering signatures at C- and Ku-bands over West Africa

Abstract:

This study presents a comprehensive comparison of radar signatures acquired over West Africa (between latitudes 0°-25°N and longitudes 5°W-25°E) at both C- and Ku-bands using nadir-looking altimeters (35-day orbital period ENVISAT RA-2 over 2003-2010 and 10-day orbital period Jason-2 over mid-2008-2011) and side-looking scatterometers (QuikSCAT over 2003-2009 and ASCAT over mid-2008-2011) that covers the major bioclimatic zones, soil and vegetation types encountered in this region.The backscattering coefficient's time series measured by both radar instruments are generated over regional transects and local sites. Meridian transects from the wet tropics to the arid regions of the Sahara desert demonstrate the spatial and temporal changes of the radar response over the West African bioclimatic gradient in terms of surface roughness, land cover and soil wetness. Nadir-looking altimetry appears more sensitive to variations of surface soil moisture than side-looking scatterometry at both C- and Ku-bands. In contrast, the impact of vegetation on the backscattered signals is found to be lower for nadir-looking instruments compared to side-looking ones.