SAR IMAGE RECONSTRUCTION WITH JOINT OFF-GRID TARGET AND PHASE ERROR CORRECTIONS

Abstract

Synthetic Aperture Radar (SAR) has significant importance in many remote sensing applications. Errors due to the platform motion or measurement model uncertainties can cause degradations in the constructed SAR images. Most of the methods deal with the phase errors which cause defocusing on the image. For efficient processing of the measurements, they discretize the fast time-slow time plane and then employ autofocus algorithms on this discrete grid. However, the reflectors which are not placed exactly on the grid degrade the image quality considerably. This is the most probable case in the practical SAR operation and it causes blur or spark like affects on the image. This is called the off-grid target problem. In this work, a Compressed Sensing based technique is developed which constructs spotlight mode SAR image, handles the off-grid target problem and makes autofocus simultaneously. A gradient descent type iterative solution is used.