A Preliminary Analysis of Wind Retrieval, Based on GF-3 Wave Mode Data.

Lei Wang,Bing Han,Qi Chen,Xinzhe Yuan,Yulin Yao,Chibiao Ding,Bin Lei

doi:10.3390/s18051604

Abstract

This paper presents an analysis of measurements of the normalized radar cross-(NRCS) in Wave Mode for Chinese C-band Gaofen-3(GF-3) synthetic aperture radar (SAR). Based on 2779 images from GF-3 quad-polarization SAR in Wave Mode and collocated wind vectors from ERA-Interim, this experiment verifies the feasibility of using ocean surface wind fields and VV-polarized NRCS to perform normalized calibration. The method uses well-validated empirical C-band geophysical model function (CMOD4) to estimate the calibration constant for each beam. In addition, the relationship between cross-pol NRCS and wind vectors is discussed. The cross-pol NRCS increases linearly with wind speed and it is obviously modulated by the wind direction when the wind speed is greater than 8 m/s. Furthermore, the properties of the polarization ratio, denoted PR, are also investigated. The PR is dependent on incidence angle and azimuth angle. Two empirical models of the PR are fitted, one as a function of incidence angle only, the other with additional dependence on azimuth angle. Assessments show that the retrieved from new PR models as well as is in good agreement with extracted from SAR images directly.

Highlights

With the continuous global depletion of petroleum energy, the development and utilization of clean wind energy have become a hot topic in recent decades
The calibration constant provided by China Centre for Resources Satellite Data and Application is derived from system bandwidth and antenna pattern and has not been verified by field calibration
2779 GF-3 Wave Mode normalized radar cross-section (NRCS) and wind vectors for the corresponding location are collected as training set and additional 1911 match-ups are as testing set

Summary

Introduction

With the continuous global depletion of petroleum energy, the development and utilization of clean wind energy have become a hot topic in recent decades. Offshore wind energy has been the focus of researchers due to the vast area of marine resources. Measurements of offshore wind information contribute to oil spill monitoring, weather forecasting and understanding of air-sea interactions [1,2,3]. Spaceborne active microwave scatterometer such as QuickSCAT and ASCAT have provided mature wind products for National Oceanic and Atmospheric Administration (NOAA) [4,5]. The wind fields acquired by scatterometer cannot be applied to fine scale marine products due to the course spatial resolution (12.5 km~25 km) [6]. Because of features like imaging in all-weather conditions and high spatial resolution, synthetic aperture radar (SAR) has been widely used in military, Sensors 2018, 18, 1604; doi:10.3390/s18051604 www.mdpi.com/journal/sensors

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Discussion

Conclusion