DOPPLER TRACKING METHOD FOR OBJECT IMAGING FROM RADAR RETURNS

A method of tracking an object in the Doppler dimension that provides for improved imaging. The method tracks the centroid of the object's Doppler and smooths out noisy estimates of its phase history. The tracking and smoothing combine to improve tracking performance and image quality. Doppler signals are generated by a coarse Doppler tracker that removes translational motion of the object. Pulse pair processing produces an estimate the Doppler centroid of the object. For each pair of adjacent pulses, pulse pair processing is applied to individual range bins, and the outputs are combined to estimate the Doppler centroid of the object at that particular time. A low pass filter is used after pulse pair processing to smooth out phase increments. Phase increment smoothing then filters the output signals from the filter with a smooth curve, such as a second-degree polynomial. Phase recursion then produces a phase history. The recursive phase history is differenced with updated, appropriately delayed phases. The difference phases are compensated from the radar return from the coarse Doppler tracker. Fast Fourier transform processing then produces a Fourier transformed image. The output from the filter is also processed to update the phase and the phase updated signals are fed back to the coarse Doppler tracker. The phase updating integrates the output of the filter to update the phase history of the object based on phase increments derived from the filter. The phase update is also delayed in order to match these phases in timing with those from the phase recursion step.