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Shadowing-analysis-based wave height measurement from ship-borne X-band nautical radar images

In this paper, a method based on shadowing analysis is applied to estimate significant wave height from ship-borne X-band nautical radar images. Edge detection is first used to extract shadowed areas from the image. The root mean square (RMS) surface slope is then derived by curve fitting illumination ratios and Smith's function. From the RMS surface slope and the mean wave period, the significant wave height is estimated. Modifications including data quality control and subareas selection are made to the analysis. It has been found that the wave height retrieved from the algorithm is underestimated under rain and overestimated under low wind speed. The method produces promising results by comparing radar-derived wave heights with buoy data, and the RMS difference is found be 0.71 m.