Sea Wind Retrieval by Analytically-Based Geophysical Model Functions and Sentinel-1a Sar Images

Abstract

In this paper, the sea surface wind speeds are retrieved by using an analytical scattering model, so called the analytically-based geophysical model function (GMF), from C-band Sentinel-1A V V-polarized synthetic aperture radar (SAR) images. The analytical models accurately simulate the rough surface scattering in the incidence angles range of SARs. The accuracy of the scattering results of the models depends on the sea wave spectrum. In this work, the effect of the sea spectral models on the accuracy of the sea surface wind speed retrieving is evaluated. In this regard, for omnidirectional and directional parts of sea spectrum, the Elfouhaily/Hwang spectra and Elfouhaily/McDaniel's models are employed, respectively. The V V-polarized backscattered normalized radar cross-section (NRCS) is calculated by using the first-order small-slope approximation (SSA1) with the four composite models of the mentioned omnidirectional spectra and angular spreading functions (directional part), and the backscattering results are compared with the empirical model CMOD6. Then, from the V V-polarized Sentinel-1A SAR data in two resolutions, the wind speeds are estimated by the analytical and empirical models. The comparison of analytical models with CMOD6 shows that Hwang-Elfouhaily model is the best among the composite models. The results show that the analytical scattering models can be easily used for the sea wind speed retrieving below 20 m/s.

Multi-Scale LG-Mod Analysis for a More Reliable SAR Sea Surface Wind Directions Retrieval

“…Among available tools, Synthetic Aperture Radar (SAR) systems are commonly used in most meteorological conditions, and they can provide wind information at high spatial resolution [4][5][6][7][8]. In spite of many methods recently proposed, the approach that exploits the dependency of SAR Normalized Radar Cross-Section (NRCS) on wind parameters (wind speed and direction), and the geometry of acquisitions (radar incidence angle) via empirical Geophysical Model Function (GMF) is still widely used [9][10][11][12][13].…”