As an important part of the earth system, the ocean surface dynamic parameters (wind, wave, current) have an important impact on air-sea interaction, ocean material and energy balance and climate change. Under the condition of spaceborne measurement, the amplitude and phase of echo contain the relevant motion information of the sea surface, which is necessary to study the Doppler spectrum characteristics formed by the high operating speed of the satellite and the sea surface dynamic parameters under the on-board condition. In this paper, a time-varying dynamic sea surface model including the main ocean dynamic parameters wind, wave and current is established by using the existing linear random superposition theory to simulate the ocean surface. Then, the backscatter coefficients of the sea surface under Bragg scattering are calculated, and their reliability is verified based on the measured data. For the study of Doppler characteristics based on Bragg scattering of moving sea surface, this paper uses the formulated OSCOM satellite parameters and sea states to obtain the Doppler spectrum including the influence of different wind parameters under the condition of Bragg scattering at medium incidence angle, and analyzes the Doppler spectrum characteristics under the influence of wind speed, wind direction, wind fetch through the spectral parameter estimation method. The analysis results of wind speeds show that the sea surface roughness and root mean square height increase with the wind speeds, resulting in the stronger backscatter modulation, and the shift and broadening of the Doppler center increase accordingly. The results of wind direction analysis show that the Doppler centroid of Doppler spectrum with wind direction is slightly asymmetric at the downwind and upwind, and reaches the minimum at 90 ° wind direction. The analysis results of the wind fetch show that when the wind speed is 10m/s and the length of wind fetch grows from a-10km-developing wave to a fully developed wave, the velocity of the sea surface increases, and the tilt modulation of the long wave increases, resulting in the Doppler shift increases, and the estimated Doppler centroid difference is 0.56m/s. Finally, the study considers the contribution of breaking wave to the co-polarized backscatter, and analyzes the influence of both on Doppler centroid and velocity estimation. The echo Doppler spectrum analysis under the condition of wave breaking shows that when the wind speed is 12m/s and the observation azimuth is the same as the wind direction, the contribution of breaking wave to Ka-band backscatter coefficient is about 4dB. Compared with the case without considering the breaking wave, the Doppler centroid offset is about 95.2Hz, resulting in a deviation of about 0.4m/s for the radial velocity estimation.
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