Radar backscatter statistics from SIR-C/X-SAR observations

Multi-frequency and multi-polarisation synthetic-aperture radar (SAR) observations of the NE Atlantic with SIR-C/XSAR are used to test models of the mean and distribution of radar backscatter from the sea surface. Although empirical and theoretical models fit well at C band, discrepancies are found at L and X band. Single-look data (spatial resolution of 7-10 m) fit well to a K distribution but multi-look data (spatial resolution of 25 m) fit a lognormal distribution. A 'quasilinear' model of ocean-wave imaging is tested by comparing the power spectra derived from the SAR image with that obtained from the simultaneous buoy measurements. Agreement is obtained only if relatively large hydrodynamic modulations are assumed in the model. Hence ocean wave modulations can account for the observed image variances.