Influence of Swell Wave on Wind Speed Retrieval Using ENVISAT ASAR Wave Mode Imagery

Duo Wang,Xiaochen Wang,Weili Jiao,Abdellah Touhafi

doi:10.1155/2021/9986523

Abstract

The main work of this paper is to explore the influence of swell wave on retrieval of wind speed using ENVISAT ASAR wave mode imagery. The normalized radar cross section (NRCS) scene under different sea states is simulated to investigate the relationship between NRCS variation with swell height, together with swell direction. Moreover, the key parameter of imagery variance (Cvar) is selected to describe the swell wave on SAR imagery. In addition, the imagery parameters of skewness and kurtosis are together analyzed as a function of collocated significant swell wave height and wind speed. Based on the analyzed results, a new method for wind speed retrieval is proposed using ENVISAT ASAR, namely, F(n). Besides the CMOD parameters of NRCS, incidence angle, and relative wind direction, the imagery parameters of Cvar, skewness, and kurtosis are used to compensate for the influence of swell wave on wind speed retrieval in F(n). Finally, the collocated European Centre for Medium-Range Weather Forecast (ECMWF) wind speed dataset and ENVISAT ASAR wave mode imagery are used to verify the retrieval precision and compare with CMOD functions. It is concluded that the F(n) model performs much better than other CMOD functions, with a correlation of 0.89, a bias of 0.08, a RMSE of 1.2 m/s, and an SI of 0.1.

Highlights

Over the past decades, multiple space-borne SAR platforms have been launched and operated for sea surface monitoring, especially for retrieval of wind vector field
The principle of geophysical model functions (GMFs) is to build a complicated relationship between the normalized radar cross section (NRCS) of copolarization SAR and wind vectors at 10 m above the sea surface [1,2,3]
The NRCS scene under different sea states is simulated to explore the relationship between NRCS variation with swell height, together with swell direction

Summary

Introduction

Multiple space-borne SAR platforms have been launched and operated for sea surface monitoring, especially for retrieval of wind vector field. For a SAR platform which operates in VV, VH, HV, and HH polarization, the semiempirical geophysical model functions (GMFs) are adapted to retrieve wind vector, such as SEASAT, ERS-1/2, ENVISAT ASAR, RADARSAT-1/2, SENTINEL-1 A/B, and GF-3. The principle of GMFs is to build a complicated relationship between the normalized radar cross section (NRCS) of copolarization SAR and wind vectors at 10 m above the sea surface [1,2,3]. The response of high wind speed to cross-polarization signal is used to resolve the saturation of sea surface NRCS in a high wind speed situation [7, 8]

Methods

Results

Discussion

Conclusion