Azimuth Correlation Models for Radar Imaging

Many applications which process radar data, including automatic target recognition and synthetic aperture radar image formation, are based on probabilistic models for the raw or processed data. Often, data collected from distinct directions are assumed to represent independent observations. This assumption is not valid for all data collection scenarios. A range of models can be developed that allow for successively more complex dependencies between measured data, up to deterministic computational electromagnetic models, in which observations from diiferent orientations have a known relationship. We consider models for the autocovariance functions of nonstationary processes defined on a circular domain that fall between these two extremes. We adopt a model of covariance as a linear combination of periodic basis functions and address maximum-likelihood estimation of the coefficients by the method of expectation-maximization (EM). Finally, we apply these estimation methods to SAR image data and demonstrate the results as they apply to target recognition.