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147 results on '"Chen, Zezong"'

11. Wave Parameter Inversion for Shipboard Coherent S-Band Radar Under Shadow Modulation

Author

Huang, Yaxuan, Chen, Zezong, Zhao, Chen, Wei, Yunyu, and Chen, Xi

Abstract

For shipboard coherent S-band radar, the shadow modulation phenomenon happens at large sea surface undulations or small grazing angles. As the ship speed increases or the sea state rises, the shadow modulation leads to an increase in the peak value of the wave spectrum, which results in inaccurate wave parameter inversion. In order to achieve accurate wave detection in high sea state or high ship speed scenarios, a shadow modulation correction method based on velocity-fitting relationship and Hermite interpolation is presented. First, the variable range of radial velocity is computed using the simulated sea surface’s velocity fitting relation. The anomalous Doppler velocity is then rectified by applying the modified Akima piecewise cubic Hermite interpolation (MAPCHI) algorithm. The MAPCHI algorithm is appropriate for complex nonlinear curves and is not prone to abrupt fluctuations or flattening issues. The implementation of this interpolation algorithm can alleviate the problem of anomalous fluctuations in Doppler velocities induced by shadow modulation. Finally, the nondirectional wave spectrum and wave parameters are calculated. Numerical simulation experiments show that the proposed method can rectify the influence of shadow modulation at various speeds and sea state backdrops. Meanwhile, comparing the radar measurements in the South China Sea with the buoy results, the mean absolute error (MAE) of significant wave height and mean wave period are 0.21 m and 0.34 s, respectively. The results demonstrate that the proposed method can successfully remove shadow modulation interference with high robustness.

Published
2024
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31. Wave Parameter Inversion From Motion-Affected Echoes Using Shipboard Coherent Microwave Radar

Author

Wu, Sitao, Zhao, Chen, Chen, Zezong, Xu, Qinghui, and Wang, Xiao

Abstract

Shipboard coherent microwave radar has been a rapidly developing tool for ocean wave measurements. However, the radial velocity estimated from echoes collected with a shipboard radar is significantly affected by the forward speed and six-degree-of-freedom (six-DOF) motion of the ship. Accordingly, the performance of ocean wave parameter inversion using such radar degrades. To address this problem, the distribution of energy modulated by the ship motion in the wavenumber–frequency spectrum is illustrated, and the wave parameters’ inversion method based on a shipboard coherent S-band radar is proposed. An adaptive filter is designed according to the distribution of the energy components modulated by the ship motion in the wavenumber–frequency spectrum. The proposed method filters out the non-wave components and preserves the wave field components. A 2-D inverse Fourier transform is applied to the filtered wavenumber–frequency spectrum to obtain the spatial–temporal radial velocities. Then the wave height spectrum is estimated from the radial velocities based on the direct relationship between the radial velocity spectrum and the wave height spectrum. Later, the significant wave height and mean wave period can be derived from the wave height spectrum. A dataset collected with the shipboard coherent S-band radar in the South China Sea in December 2020 is analyzed. The ship deployed with the radar sailed around a wave buoy according to a route plan for two days in that experiment. Comparisons between the radar-estimated and buoy-measured measurements in cases of ship motion are conducted. The results indicate that the proposed method can invert wave parameters well.

Published
2023
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