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Ocean surface wind speed retrieve from co-polarized SAR using composite surface bragg scattering model

  • role： First author第一作者
  • Affiliation：

    Zhejiang Climate Centre, Hangzhou 310051, China

    State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China

  • Email：fanghe_doc@163.com
  • Introduction：方贺，研究方向为海洋微波遥感技术。E-mail： fanghe_doc@163.com
FANG He12,  
  • Affiliation：

    State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China

YANG Jingsong2,  
  • Affiliation：

    Zhejiang Climate Centre, Hangzhou 310051, China

FAN Gaofeng1,  
  • role： Corresponding author通信作者
  • Affiliation：

    Jiangsu Meteorological Observatory, Nanjing 210008, China

  • Email：44183130@qq.com
  • Introduction：李超，研究方向为海洋遥感和海气相互作用。E-mail： 44183130@qq.com
LI Chao3*,  
  • Affiliation：

    Lianyungang Meteorological Observatory, Lianyungang 222002, China

SHI Dawei4,  
  • Affiliation：

    Fisheries & Oceans Canada, Bedford Institute of Oceanography, Dartmouth NS B2Y 4A2, Canada

WILLIAM Perrie5

résumé

Composite Surface Bragg Scattering (CSBS) model is a classical ocean microwave scattering model, which can describe the Normalized Radar Cross Section (NRCS) of microwave backscattering from a rough ocean surface. The CSBS model includes a Bragg model and a geometric optics model and can be used to retrieve ocean surface wind speed from spaceborne synthetic aperture radar (SAR). Compared with Geophysical Model Function (GMF) developed by methods of empirical statistics, the CSBS model works well at all microwave frequencies. Reports showed that geometric optics model is most suitable for small local incidence angles, whereas Bragg model tends to be best for moderate incidence angles. In other words, for local radar incidence angles that are smaller than a given angle setting, the two-scale backscattering mechanism of the sea surface is replaced by a geometric optic solution for specular reflection. However, determining the threshold for small and moderate local incidence angles is still an open question. The local incidence angle search algorithm is proposed and developed to find the optimal radar incidence angle at co-polarized (VV-and HH-polarized) channel. The modeling data for the local incidence angle search algorithm include wind speed data retrieved from 142 Canada RADARSAT-2 fine-beam quad-polarized SAR images in the east coast of America, the west coast of America, and the East China Sea. Ocean surface wind speed measured from the National Data Buoy Center (NDBC), the Environment and Climate Change Canada (ECCC) and the China State Oceanic (SOA) are considered reference wind speed. The conclusion shows that the optimal setting of 14 and 16 degrees is the optimal radar incidence angle for ocean surface wind speeds retrieve from CSBS model at VV-and HH-polarized RADARSAT-2 SAR images. Based on the optimal incidence angle setting, ocean buoy-measured wind speed data are considered references, and ocean surface wind speed is retrieved from VV-and HH-polarized RADARSAT-2 SAR data using CSBS model at 0—15 m/s wind condition. Results show that the ocean surface wind speeds retrieved from RADARSAT-2 fine-beam quad-polarized SAR data using CSBS model at VV- and HH-polarized channel are in good agreement with in situ ocean buoy wind speed. The root mean square error (RMSE) of SAR-retrieved wind speed and buoy-measured wind speed are 2.15 m/s (VV-polarized channel) and 2.32 m/s (HH-polarized channel), and the correlation coefficients are 0.79 (VV-polarized channel) and 0.75 (HH-polarized channel), which are statistically significant at 99.9 significance level. The conclusion of this article indicated that the optimized incidence angle setting of the CSBS model found in our study has good applicability and reliability under low-to-moderate ocean surface wind speed (no higher than 15 m/s). From case comparisons of the CBS model with RADARSAT-2 SAR images, the optimized small incidence angle setting of 14 and 16 degrees of the CBS model is suitable for the microwave frequency of the C-band with co-polarization. More studies on the optimized small incidence angle setting of the CBS model and its application in other microwave frequencies, cross polarizations, or high sea states will be considered in future investigations.

mots-clés

remote sensing;electromagnetic model;synthetic aperture radar;sea surface wind speed;geophysical model functions

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