Calibrating SeaWinds and QuikSCAT scatterometers using natural land targets

The SeaWinds-on-QuikSCAT (QuikSCAT) and SeaWinds-on-ADEOS-2 (SeaWinds) scatterometers measure the normalized radar backscatter (σ^o) of the earth´s surface. These identical radar sensors are on different spaceborne platforms in similar orbits. QuikSCAT and SeaWinds data are used to infer near-surface wind vectors, polar sea-ice extent, polar-ice melt events, etc. In order to verify the relative calibration of these sensors, a simple cross calibration based on land backscatter measurements is performed. A first-order polynomial model is used to remove the incidence angle dependence of σ^o for selected regions of the Amazon rainforest and the Sahara Desert. It is shown that the two sensors are well-calibrated to each other and require no bias corrections. Additionally, evidence of a diurnal cycle in the Amazon rainforest backscatter is given.