Reflectivity models for radar target recognition

A model for the generation of reflectivity profiles is presented for use in a radar target recognition system. The data are assumed to come from two sensors: a high range resolution radar and a tracking radar. The object is simultaneously tracked and identified using estimation theoretic methods by comparing a sequence of received range profiles to range profiles generated from surface templates. The tracking data are used to form priors on the position and orientation of the object. The templates consist of surface descriptions comprised of electromagnetically large patches tiling the entire object. The predicted return is computed from several quantities. First, the reflectivity range profile is computed from the patches incorporating a shading function. The physical optics approximation is that patches not directly illuminated by the transmitted signal do not contribute to the return signal. Second, the reflected signal is approximated by the convolution of the transmitted signal with the range profile. Third, the receiver design yields the actual I-Q data available for processing. The tracking is performed using advanced models of aircraft of interest. Given measurements of the bulk position and velocity of the aircraft, the other states (orientation, angular rates, other velocities) are estimated. These estimates and a quantitative measure of the quality of the estimates (as provided, for example, by an extended Kalman filter) are used in the prediction of the range profiles. They also may be used in a preliminary object discrimination step based solely on the dynamics. The models for the available data are based on radars in use at Rome Laboratory in Rome, NY. The high range resolution data comes from an S-band radar which transmits chirp pulses and uses stretch processing in the receiver. The processing is performed on a DEC/MPP computer with 4096 processors. Preliminary results are encouraging.