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Optical flow-based method to estimate internal wave parameters from x-band marine radar images

Acta Oceanologica Sinica 2022年第9期41卷 149-157页

作者： Jinghan Wen Zhongbiao Chen Yijun He School of marine Sciences Nanjing University of Information Science&TechnologyNanjing210044China Key Laboratory of Space Ocean Remote Sensing and Applications National Satellite Ocean Application ServiceBeijing100081China

The velocity and direction of internal waves(IWs) are important parameters of the ocean,however,traditional observation methods can only obtain the average parameters of IWs for a single location or large ***,a new method based on optical flow is proposed to derive the phase velocity vectors of IWs from x-band marine radar ***,the x-band marine radar image sequence is averaged,and ramp correction is used to reduce the attenuation of gray values with increasing radial ***,the average propagation direction of the IWs is determined using the two-dimensional Fourier transform of the radar images;two radial profiles along this direction are selected from two adjacent radar images;and then,the average phase velocity of the IWs is estimated from these radial ***,the averaged radar images are processed via histogram equalization and binarization to reduce the influence of noise on the radar ***,a weighting factor is determined using the average phase velocity of a reference point;the phase velocities on the wave crest of the IWs are subsequently estimated via the optical flow ***,the proposed method is validated using x-band marine radar image sequences observed on an oil platform in the South China Sea,and the error of the phase velocity is calculated to be 0.000 3–0.073 8 m/*** application conditions of the proposed method are also discussed using two different types of IW packets.

关键词： internal wave x-band marine radar optical flow phase velocity

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A new modulation transfer function for ocean wave spectra retrieval from x-band marine radar imagery

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Chinese Journal of Oceanology and Limnology 2015年第5期33卷 1132-1141页

作者：陈忠彪张彪何宜军丘仲锋 PERRIE William Nanjing University of Information Science and Technology Bedford Institute of Oceanography

When imaging ocean surface waves by x-band marine radar, the radar backscatter from the sea surface is modulated by the long surface gravity waves. The modulation transfer function （MTF） comprises tilt, hydrodynamic, and shadowing modulations. A conventional linear MTF was derived using HH-polarized radar observations under conditions of deep water. In this study, we propose a new quadratic polynomial MTF based on W-polarized radar measurements taken from heterogeneous nearshore wave fields. This new MTF is obtained using a radar-observed image spectrum and in situ buoy-measured wave frequency spectrum. We validate the MTF by comparing peak and mean wave periods retrieved from x-band marine radar image sequences with those measured by the buoy. It is shown that the retrieval accuracies of peak and mean wave periods of the new MTF are better than the conventional MTF. The results also show that the bias and root mean square errors of the peak and mean wave periods of the new MTF are 0.05 and 0.88 s, and 0.32 and 0.53 s, respectively, while those of the conventional MTF are 0.61 and 0.98 s, and 1.39 and 1.48 s, respectively. Moreover, it is also shown that the retrieval results are insensitive to the coefficients in the proposed MTF.

关键词： x-band marine radar modulation transfer function ocean wave spectra

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