Micro-Doppler Analysis of Rotating Target in SAR

摘要

Rotating targets cause phase modulation of the azimuthal phase history of a SAR system. The phase modulation may be seen as a time-dependent micro-Doppler (m-D) frequency. Due to their superior resolution potential, it is useful to analyze such signals with time-frequency analysis methods. This report presents two approaches for extracting m-D features from SAR images. In order to extract m-D features from SAR images, the time domain radar return is decomposed in two separate ways. One is based on wavelet decomposition in which the returned signal is decomposed into a set of components that are represented at different wave let scales. The components are then reconstructed by applying the inverse wavelet transform. This wavelet approach has been used in our previous m-D analysis work for a ISAR system, and it is presented here in the extraction of m-D features for a SAR system. The second approach is based on adaptive chirplet decomposition. This new approach is introduced as an alternative to the wavelet approach of decomposing the SAR radar return. The results from the wavelet and adaptive chirplet decomposition procedures are compared, and the chirplet-based approach establishes itself as a viable alternative. The chirplet based method of m-D extraction has been successfully applied to SAR data scene collected by the US Navy APY-6 radar. The rotating frequency of the antenna was calculated using this method and the results agree well with available ground truth data.