Abstract
Within the framework of the two-scale scattering model, the Doppler shift of C-band radar return signals from the nonlinear sea surface are numerically evaluated. As an analytical approximation method, the Bragg resonance scattering method cannot accurately describe the backscattering field from sea surface. Therefore, in the two-scale scattering model, more accurate scattering coefficient (the normalized radar cross section, NRCS) evaluated by the C-band dual-polarized (HH/VV) empirical geophysical model function (CSAR model) is employed to replace the traditional Bragg NRCS to weight the Doppler shift. The numerical results indicate that there are obvious differences between the Doppler shift weighted by the CSAR NRCS and that weighted by the traditional Bragg NRCS. The hydrodynamic modulation of the large-scale waves is one of the important factors that affect the difference between the Doppler shift predicted in upwind and downwind directions. If the relaxation rate in the hydrodynamic modulation is set to be the angular frequency of the dominant water waves, the Doppler shift predicted by the numerical method can fit the results of the empirical model (C-band empirical geophysical model function, CDOP) well at moderate wind speed. Under low wind condition, the comparison shows that the empirical CDOP model appears to overestimate the Doppler shift. In order to facilitate the application, at the end of this paper a semi-empirical CSAR-DOP model, which is a polynomial fitting formula, is developed for evaluating the Doppler shift of C-band signals from time varying sea surface.
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Foundation item: The National Natural Science Foundation of China under contract No. 41976167; the Key Research and Development Program of Shandong Province (International Science and Technology Cooperation) under contract No. 2019GHZ023.
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Cui, J., Wang, Y., Zhang, Y. et al. A new model for Doppler shift of C-band echoes backscattered from sea surface. Acta Oceanol. Sin. 42, 100–111 (2023). https://doi.org/10.1007/s13131-022-2144-8
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DOI: https://doi.org/10.1007/s13131-022-2144-8