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摘要

北极海域的海浪与海冰相互作用是目前北极海冰变化研究的一个前沿问题。但观测数据的缺失,限制了对于该问题的深入研究。星载合成孔径雷达(Synthetic Aperture Radar,SAR)具有独特的海面二维成像能力,是极地边缘区海浪-海冰相互作用研究重要的遥感手段。本文基于哨兵1号干涉宽幅模式(Interferometric Wide Swath,IW)数据,利用SAR海浪非线性反演方法在格陵兰海及挪威海开展了海浪方向谱的反演实验,进而使用中法海洋卫星CFOSAT搭载的SWIM波谱仪的海浪谱数据和星下点有效波高数据对SAR反演结果进行了验证。结果表明,无论是海浪方向谱的结构、能量分布特征还是海浪方向谱的积分参数,SAR的反演结果都与SWIM的测量结果具有良好的一致性。其中,SAR海浪方向谱和SWIM斜率谱积分计算的有效波高的偏差和均方根误差为0.11 m和0.71 m,平均波周期的偏差和均方根误差分别为-1.02 s和1.08 s,谱峰传播方向与波长的绝对偏差分别为13.16 °和32.48 m, 均方根误差分别为19.10°和44.10 m。SAR反演的有效波高与SWIM星下点测量的有效波高之间偏差为0.03 m,均方根误差为0.48 m,二者相关系数为0.95。本研究验证了利用SAR海浪非线性反演方法进行北极海域海浪方向谱及海浪参数反演的可行性,为后续的海浪向冰传播衰减过程研究奠定了数据基础和方法基础。
关键词:
北极,海浪,SAR,CFOSATThe interaction between ocean waves and sea ice in the Arctic ocean has drawn great attention on. However, due to the lack of observation data, the study on this topic is significantly limited. Synthetic aperture radar (SAR) has the unique capability of imaging sea surface in two-dimension, which therefore, plays an important role in the study on interaction between ocean wave and sea ice. In this study, we used the MPI method to retrieve ocean wave spectra from Sentinel-1(S1) Interferometric Wide Swath (IW) data. The retrieved results were compared with SWIM measurements of both ocean wave slope spectra at incident angle of 10° and significant wave height (SWH) at nadir. The experiment was carried out using the data acquired in September 2020 in the Greenland Sea and Norwegian Sea, where the ocean waves generated in the North Atlantic and propagate long distance to the ice-covered area in the Arctic ocean can be observed frequently. 54 ocean wave spectra are retrieved from 25 IW data and are compared with SWIM slope spectra. The comparison shows that the SAR-retrieved spectra are consistent with SWIM spectra in structure and energy distribution. The good agreements are also found between the integral parameters of SAR ocean wave spectra and SWIM slope spectra. The comparison yields a bias and an RMSE of 0.11 m and 0.71 m for SWH, a bias and an RMSE of -1.02 s and 1.08 s for mean wave period (MWP). The comparisons of the dominant wave parameters yield an absolute bias of 13.16° and an RMSE of 19.10° for dominant wave direction, an absolute bias of 32.48 m and an RMSE of 44.10 m for dominant wavelength. Furthermore, 5, 075 data pairs of S1-retrieved SWH and SWIM nadir SWH were collocated and compared. The comparison result yields a bias of 0.03 m and an RMSE of 0.48 m, the correlation between the two dataset is 0.95. Both the comparisons of wave spectra and wave parameters show good agreements, which suggests that it is feasible and effective to retrieve ocean wave information from S1 IW data by MPI method in the Arctic ocean. This will be of great support for further study on interaction between sea ice and ocean waves.