No abstract

Consider the effect of spray droplets and foams on the radar altimeter, an improved algorithm of retrieving oceanic surface wind speed is proposed in this study. Firstly, a four‐layer medium model is established in order to simulate accurately the air–sea interface. Secondly, the microwave reflectivity of the established model is computed at 13.5 GHz. The computed results show that the effect of spray droplets and foams plays an important role in the reflectivity of the air–sea surface and causes it to decline from 0.6 to 0.23. Thirdly, the computed results are applied to retrieve the sea surface wind speed and an improved algorithm of retrieving wind speed is proposed. At low wind speeds, the improved algorithm is in good agreements with those reported results, and at high wind speeds is also in good agreements with some empirical algorithms presented by Brown, Young and so on. Finally, the improved algorithm can improve the sea surface wind speed retrieval more effectively and also is closer to the actual situation of the sea surface than those algorithms based on the three‐layer medium model.

At high sea states strong winds make the sea surface broken, and become a multilayer-rough sea surface made of a large number of foams and droplets. Similarly, if the sea surface covered by oil and other dirts will also belong to the mutilayer rough sea surfaces of various medium properties. In this paper, applying the Kirchhoff Approximation (KA) and the electromagnetic theory of stratified media, electromagnetic scattering characteristics from a multilayer rough medium surface are calculated. Firstly, a detailed analysis of electromagnetic reflection from multilayer parallel interfaces under different incident angles is carried out. Secondly, combining the preceding two results and courses, electromagnetic scattering from the multilayer random rough surfaces is studied. The computed results are in good agreement with those by using the method of moments (MOM) and reported by some experts. Finally, the random rough sea surface covered by spilling oil or droplets and foams is calculated in detail. Compared with MOM, the new approximate analysis method in the paper can avoid a large matrix inversion, and thus greatly reduce the computation time and improve the computational efficiency.

Considering about the effect of whitecaps and foams on pulse-limited Radar Altimeters, an improved algorithm of retrieving sea surface wind speed is proposed in this paper. Firstly, a four-layer dielectric model is established in order to simulate an air-sea interface. Secondly, the microwave reflectivity of a sea surface covered by spray droplets and foams at 13.5 GHz is computed based on the established model. These computed results show that the effect of spray droplets and foams in high sea state conditions shall not be negligible on retrieving sea surface wind speed. Finally, compared with the analytical algorithms proposed by Zhao and some calculated results based on a three-layer dielectric model, an improved algorithm of retrieving sea surface wind speed is presented. At a high wind speed, the improved algorithm is in a better accord with some empirical algorithms such as Brown, Young ones and et al., and also in a good agreement with ZT and other algorithms at low wind speed. This new improved algorithm will be suitable not only for low wind speed retrieval, but also for high wind speed retrieval. Better accuracy and effectiveness of wind speed retrieval can also be obtained.