It is difficult to retrieve the ocean wind direction using the specular reflection signal owing to its insensitivity to the sea surface wind direction. The sensitivity of the scattered Global Navigation Satellite System-Reflectometry (GNSS-R) signal from the non-specular geometry to wind direction is first investigated in this paper. The sub-satellite non-specular observation mode is proposed, and the observable quanitity sensitive to wind direction in this mode is defined. Based on this mode, the wind vector retrieval algorithm using spaceborne GNSS-R based on the Maximum Likelihood Estimation (MLE) is presented, in which the sub-satellite non-specular scattering signals from two and more navigation satellites are used to retrieve ocean wind vector. A simulator is developed to demonstrate and test the proposed algorithm. The results show that due to the ambiguity of the observation geometry and the symmetry of the ocean spectrum, there are four uncertain solutions in the retrieved wind directions. The ambiguity of the measurement geometry can be eliminated by using the multi-satellite observation, and only two possible solutions of wind directions still are remained. When the scattered signals from three satellites are used, and the Signal-to-Noise Ratio (SNR) is over 11 dB, the Root Mean Square Error (RMSE) of the retrieved wind speed and direction are less 2 m/s and 15° with a wind speed rang of 2～25 m/s.
维普
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