A novel algorithm for ocean wave direction inversion from X-band radar images based on optical flow method
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A novel algorithm for ocean wave direction inversion from X-band radar images based on optical flow method WANG Li1, CHENG Yunfei1*, HONG Lijuan1, LIU Xinyu1 1 Third Research Institute, Ministry of Public Security, Shanghai 200031, China
Received 11 May 2017; accepted 15 June 2017 ©The Chinese Society of Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
As one of the important sea state parameters for navigation safety and coastal resource management, the ocean wave direction represents the propagation direction of the wave. A novel algorithm based on an optical flow method is developed for the ocean wave direction inversion of the ocean wave fields imaged by the X-band radar continuously. The proposed algorithm utilizes the echo images received by the X-band wave monitoring radar to estimate the optical flow motion, and then the actual wave propagation direction can be obtained by taking a weighted average of the motion vector for each pixel. Compared with the traditional ocean wave direction inversion method based on frequency-domain, the novel algorithm is fully using a time-domain signal processing method without determination of a current velocity and a modulation transfer function (MTF). In the meantime, the novel algorithm is simple, efficient and there is no need to do something more complicated here. Compared with traditional ocean wave direction inversion method, the ocean wave direction of derived by using this proposed method matches well with that measured by an in situ buoy nearby and the simulation data. These promising results demonstrate the efficiency and accuracy of the algorithm proposed in the paper. Key words: X-band radar, optical flow, weighted average, ocean wave direction, radar image Citation: Wang Li, Cheng Yunfei, Hong Lijuan, Liu Xinyu. 2018. A novel algorithm for ocean wave direction inversion from X-band radar images based on optical flow method. Acta Oceanologica Sinica, 37(3): 88–93, doi: 10.1007/s13131-018-1201-9
1 Introduction The state of ocean wave is regarded as the focal point of ocean research, which is closely related to human beings activities. For now, the ocean wave is an important and meaningful ocean environment parameter. It has significant meaning for shore protection, ocean development, ocean environmental protection, and ocean military affairs. Sea state parameters such as wave height, wave period, and wave direction are numerical information which have a direct link to the wave motion. As one of the important sea state parameters for a navigation safety and a coastal resource management, the ocean wave direction represents the propagation direction of the wave. The monitoring of the sea state by a X-band radar is of timely interest because this kind of radar gives the opportunity to scan the sea surface with high temporal and spatial resolutions under various sea conditions in the near range ( ≥ 5 km) of the X-band radar (Young et al., 1985; Senet et al., 2008). The X-band radar echo signal is usually displayed as gray-level i
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