Multiple discrete autofocus

Abstract

A method and autofocus processor that is adapted to automatically correct focus phase errors associated with synthetic array radar signals. The method comprises processing the synthetic array radar signals to produce a SAR image; identifying and locating potential targets contained in the SAR image; storing the range bin and azimuth location of the target in a target list; bandpass filtering the SAR signals associated with the target scatterer to remove the interference therefrom; forming the pulse pair product of the phase history samples from each reference target to produce a differential phase function; integrating the differential phase function over all reference targets to provide the averaged differential phase history associated therewith; interpolating the averaged differential phase function to restore the original time scale and number of samples; and computing the focus error from interpolated differential phase history. The focus error is estimated as a weighted average of the phase history of the detected scatterers. The autofocus processor automatically finds targets and combines data from multiple scatterers effectively and efficiently. The autofocus processor extends the range and resolution limits of SAR systems, and enables the effective use of a SAR sensor with less expensive motion compensation function. The autofocus processor also decouples the SAR sensor (including motion sensors) from its SAR processor, so that the autofocus processor produces better images, no matter what sensor is employed.