A Simple Method of Estimating Wave Height Based on Shadowing in X-Band Radar Images

X-band marine radar shadow features are widely applied to wave height estimation. Since the shadow fraction rises with the distance from the radar antenna, wave slope estimation is sensitive to the selected analysis region. To resolve this issue, a wave height estimation method is proposed by adopting the optimal shadowed fraction which is unrelated to the boundary selection of the analysis area. Within this paper, the shadow fraction is computed on the basis of the mechanism of radar image shadow imaging. Instead of adopting the widely used Smith fitting function, the wave slope with the non-shadow areas is achieved by using the obtained shadow fraction and the grazing angle. The collected marine radar images, totaling 450 h, are employed to demonstrate the performance of the proposed wave height retrieval method. Compared with fundamental shadow statistical approach, the root mean square error of the proposed method decreases by 0.19 m, and the correlation coefficient increases by 0.10. Meanwhile, the execution time of the presented algorithm has significantly decreased.