Doppler Centroid Estimation of Doppler Scatterometer Based on Deramping

A Doppler scatterometer is a kind of rotating radar, which uses a real aperture system and has a high pulse repetition frequency (PRF), so it has the ability to provide useful Doppler information for ocean current field estimation. In previous studies, the Doppler centroid estimation of the Doppler scatterometer was calculated by the average cross-correlation coefficient (ACCC) method. Although this method is fast and robust, it does not make full use of the shape characteristics of the antenna pattern. The estimation method based on the Doppler spectrum can improve accuracy. However, this method is mainly used in radar systems with fixed azimuth, but the antenna of the Doppler scatterometer is always rotating, so this method cannot be directly applied. To improve the estimation accuracy of the Doppler centroid, this paper proposes an optimal estimator method for the Doppler centroid based on deramping and gives the estimation accuracy model of this method based on the Cramer-Rao bound. Doppler centroid estimation based on the Doppler spectrum requires a large scanning accumulation time to obtain high-precision results, and the bandwidth will increase with the increase of accumulation time, eventually exceeding the PRF, resulting in Doppler ambiguity. This method sets a reference function through deramping to move the Doppler centroid of each target to near zero frequency. In this way, the bandwidth is only related to the illumination time of the target, but independent of the scanning accumulation time. The effectiveness, feasibility and accuracy of the method are verified by simulation experiments. It is verified that this method not only solves the Doppler ambiguity caused by azimuth scanning but also improves the estimation accuracy of the Doppler centroid. Compared with the classical ACCC method, the estimation accuracy of this method is improved by 26.15%.