Marine Science and Technology College, Zhejiang Ocean University, Zhoushan 316022, China.
National Satellite Ocean Application Service, State Oceanic Administration, Beijing 100081, China.
Sensors (Basel). 2018 Jun 28;18(7):2064. doi: 10.3390/s18072064.
The motivation of this work is to explore the possibility of typhoon wave retrieval (the main parameter is significant wave height (SWH)) for C-band Gaofen (GF-3) synthetic aperture radar (SAR) with a wide swath coverage (>400 km). We aim to establish an analysis of a typhoon wave in the subresolution-scale (approximately 20 × 20 km²) on GF-3 SAR through SAR-measured parameters, including a normalized radar cross section (NRCS) and variance of the normalized SAR image (herein called cvar), which are the basic variables in an empirical wave retrieval algorithm and are independent of visible wave streaks. Several typhoons around the China Seas were captured by Chinese GF-3 SAR in 2017; e.g., Noru, Doksuri, Talim and Hato. The wave fields simulated from the third-generation numerical wave model WAVEWATCH-III (WW3) are collocated with these images. In general, the distribution patterns of the typhoon waves from the WW3 model are consistent with wave fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) at 0.125° grids, indicating that the simulation results from the WW3 model are suitable for our study. In addition to winds retrieved from GF-3 SAR images in vertical-horizontal (VH) polarization, the characteristics of the typhoon wave on vertical-vertical (VV) polarization GF-3 SAR images are studied. It is found that SWH has a linear relationship with NRCS and cvar, however, SWH fluctuates with wind speed at all incidence angles. Based on the analyzed results, we simply tune two empirical wave retrieval algorithms for GF-3 SAR in typhoons. Although the correlation (COR) reaches 0.5 taking account into the NRCS term, a more accurate retrieval algorithm, including more related terms, is anticipated for further development for GF-3 SAR and validated through more typhoon images.
这项工作的目的是探索利用具有宽幅覆盖（超过 400 公里）的 C 波段高分三号（GF-3）合成孔径雷达（SAR）进行台风波反演（主要参数为有效波高（SWH））的可能性。我们旨在通过 SAR 测量的参数（包括归一化雷达截面（NRCS）和归一化 SAR 图像方差（简称 cvar））来分析 GF-3 SAR 亚分辨率尺度（约 20×20km²）内的台风波，这两个参数是经验波反演算法中的基本变量，与可见的波条纹无关。2017 年，中国 GF-3 SAR 捕获了多个中国海域附近的台风，如诺鲁、杜苏芮、谭美和哈托。从第三代数值波浪模型 WAVEWATCH-III（WW3）模拟的波场与这些图像相匹配。总的来说，WW3 模型的台风波分布模式与欧洲中期天气预报中心（ECMWF）0.125°网格的波场一致，表明 WW3 模型的模拟结果适合我们的研究。除了从 GF-3 SAR 图像的垂直-水平（VH）极化中反演的风之外，还研究了 GF-3 SAR 垂直-垂直（VV）极化图像上的台风波特征。结果表明，SWH 与 NRCS 和 cvar 呈线性关系，然而，在所有入射角下，SWH 都随风速波动。基于分析结果，我们简单地调整了两个用于 GF-3 SAR 台风的经验波反演算法。尽管考虑 NRCS 项后相关系数（COR）达到 0.5，但预计对于进一步开发 GF-3 SAR，需要一个包括更多相关项的更准确的反演算法，并通过更多的台风图像进行验证。
