Analysis of Data-Derived SeaWinds Normalized Radar Cross-Section Noise

The normalized standard deviation ((Formula presented.)) of the noise that affects scatterometer Normalized Radar Cross-Sections ((Formula presented.) s) plays a key role in the ocean and more in particular coastal wind retrieval procedures and the a posteriori quality control. This paper presents a method based on SeaWinds measurements to estimate (Formula presented.) s. The method computes the standard deviation of the differences between the full-resolution (slice) (Formula presented.) s and the footprint (egg) (Formula presented.). The results are compared to the median of (Formula presented.) s provided with SeaWinds (Formula presented.) s, showing some non-negligible differences. (Formula presented.) s estimated on non-homogeneous surfaces are larger than those estimated on sea, whereas no differences are appreciated in the provided (Formula presented.) s, which is likely due to the ability of this methodology to account for the effect of the scene variability in the estimates. The presence of inter-slice biases is demonstrated with a trend with the antenna azimuth angle. A multi-collocation slice cross-calibration procedure is suggested for the retrieval stage. Finally, a theoretical model of the distribution of (Formula presented.) s is proposed and used to validate (Formula presented.) s. The results prove the efficacy of this model and that the provided (Formula presented.) s seem to be largely underestimated at low-wind regimes.