Analysis of Envisat RA2 altimeter sigma-nought bloom events for S and Ku bands backscattering intercomparison

The RA2 radar altimeter onboard the European Satellite Envisat is a double band microwave instrument working at Ku- and S-band. The S-band measurements provide appropriate atmospheric corrections for the more precise Ku-band measurements, but are also used in conjunction with the Ku-band data in order to investigate the underlying surface. In this study we try to identify differences and similarities of the backscatter signal in the two bands. We focus our attention on the condition of specular alike radar returns, which mostly occur on sea-ice regions. An attempt to find situations in which highly correlated radar waveforms in the two bands can be ascribed to simple scattering mechanisms is made in order to find indications on the mutual calibration of the two channels. The paper reports a number of cases ancountered while analyzing RA-2 data. Both level 2 (1 Hz geophysical parameters) and level 1 (18 Hz waveforms) have been used.