Wave Height Estimation from Shadowing Based on the Acquired X-Band Marine Radar Images in Coastal Area

Abstract

Abstract:In this paper, the retrieving significant wave height from X-band marine radar images based on shadow statistics is investigated, since the retrieving accuracy can not be seriously affected by environmental factors and the method has the advantage of without any external reference to calibrate. However, the accuracy of the significant wave height estimated from the radar image acquired at the near-shore area is not ideal. To solve this problem, the effect of water depth is considered in the theoretical derivation of estimated wave height based on the sea surface slope. And then, an improved retrieving algorithm which is suitable for both in deep water area and shallow water area is developed. In addition, the radar data are sparsely processed in advance in order to achieve high quality edge image for the requirement of shadow statistic algorithm, since the high resolution radar images will lead to angle-blurred for the image edge detection and time-consuming in the estimation of sea surface slope. The data acquired from Pingtan Test Base in Fujian Province were used to verify the effectiveness of the proposed algorithm. The experimental results demonstrate that the improved method which takes into account the water depth is more efficient and effective and has better performance for retrieving significant wave height in the shallow water area, compared to the in situ buoy data as the ground truth and that of the existing shadow statistic method.

Influence of Sea Surface Current on Wave Height Inversion in Shadow Statistical Method

“…In this paper, the influence of surface current is investigated. From the experimental results in [17] and this paper, it can be observed that considering both the wave depth and the surface current can improve the retrieving accuracy of wave height. However, the water depth has a greater effect for improving the retrieving accuracy than the surface current, compared to the experimental result in [17].…”

“…From the experimental results in [17] and this paper, it can be observed that considering both the wave depth and the surface current can improve the retrieving accuracy of wave height. However, the water depth has a greater effect for improving the retrieving accuracy than the surface current, compared to the experimental result in [17]. The reason is that the observation area of the collected radar belongs to the shallow water area and the retrieving accuracy is greatly affected by water depth.…”

“…Under the same sea conditions, the effect of surface current on retrieving the significant wave height by using the synthetic radar images is investigated in below. To certify the influence of the sea surface current on the wave height inversion, based on the Joint North Sea Wave Project (JoNSWaP) spectrum, the method in [17] is used to generate the simulated sea surface elevation images and polar radar images. To simplify the simulation, the shadow modulation is mainly considered.…”

“…When the influence of sea surface current is considered by using the shadow statistical method, the correlation coefficient between the calculated wave height and the buoy record is larger than that of ignoring the influence of sea surface current, and the RMSE of the obtained wave height is smaller than that of ignoring the influence of sea surface current. In [17], the effect of water depth is considered for retrieving wave height based on the shadow statistical method. In this paper, the influence of surface current is investigated.…”

“…By studying the sea surface slope formula for calculating significant wave height in the shadow statistical method, it is found that the formula is deduced under the assumption of infinite water-depth and the influence of surface current is not considered in the process of derivation. Thus, the influence of the water-depth on the inversion accuracy is considered [17]. The improved inversion formula of wave height is suitable for both shallow water and deep water conditions.…”