V. Kerbaol, B. Chapron

The European SPACE Agency ERS-1 and ERS-2 C-band VV-polarization intruments (AMI) offer the unique ability to combine interlaced scatterometer and SAR wave modes. The 10km x 4km local images are obtained every 200 km along the satellite track. For this study, more than 2000 imagettes were used. All these imagettes have been thouroughly treated.

This careful statistical analysis has been carried out in comparison with normalized radar cross section (NRCS) measurements from the scatterometer mode. During the ERS-1 AMI-wave mode mission, the incidence angle of the imagette center has been modified from about 19 degree to 23 degree. Using ERS-1 and ERS-2 NRCS, calibration effort has thus been completed for both configuration which allows to better characterize some saturation effects.

On the other hand, since a SAR only relies on its platform displacement to achieve fine resolution, the motion of surface reduces its nominal resolution. As the wind speed increases, migrations occuring during the SAR integration time increase, and are characterized by large cutoff wavelengths. Global comparison between the different statistical parameters and estimated cutoff wavelengths are presented. Explicit relationships are observed between these spectral and statistical characteristics. Acknowledging the strong dependence between sea state conditions and smearing effects, our results are then highlighted by the global comparison with wind estimates derived from the scatterometer. The results demonstrate the ability to define a SAR wind algorithm from a kinematic point of view. The relationships are not obtain to the detriment of more standard SAR scatterometry algorithm developments. Thus, such an analysis will complement the local geophysical information and will especially help to refine local SAR wind estimates.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry