Radar backscatter statistics from the sea surface: Implications of SIR-C/X-SAR observations from the NE Atlantic

Multichannel synthetic aperture radar (SAR) observations from the spaceborne imaging radar-C/X-band SAR (SIR-C/X-SAR) experiment in the NE Atlantic (April 1994) are analyzed to test models of both the mean and the distribution of radar backscatter from the sea surface. The data cover incidence angles from about 20 degrees to 40 degrees and wind speeds from about 5 to 10 m s(-1). Empirical models of the mean fit the data well at C band to an accuracy of within 1-2 dB. Discrepancies at L band are a function of incidence angle, and we cannot rule out the possibility that they arise from systematic calibration errors. Single-look SIR-C/X-SAR data (spatial resolution similar to 7-10 m) fit well to a K distribution, but multilook data (spatial resolution similar to 25 m) fit better to a lognormal distribution. The observed second moments of image intensity can be explained by the modulations of resolved ocean surface waves but only if relatively large hydrodynamic modulations, which are generally consistent with those inferred from tower radar data, are assumed.