Phase error estimation algorithm: theory, applications, and examples

A range-Doppler image is corrupted when each pulse in the corresponding range-time array contains a single time-dependent phase error. An algorithm is developed to estimate these phase errors; the errors are removed, and range-Doppler imaging proceeds in the usual manner. The iterative algorithm works homogeneously across the range-time array (no bright scatterers are necessary for focusing). The estimation technique is model based, but image recovery is successful for images that do not fit the model. The technique promises to be a valuable tool for phase recovery in many cases. These may include image recovery for radar data that: (1) were recorded by a system incapable of maintaining coherence; (2) have been corrupted by uncalibrated sensor or target motion; (3) were collected using frequency- jumped center frequencies; (4) have been corrupted due to the ionosphere; or (5) are bistatic radar data received from a noncooperative transmitter. Illustrations of case (1) are provided, using simulations, postmission corrupted field data, and data that are inherently noncoherent.