Introduction - If you have any usage issues, please Google them yourself
The Phase Gradient Autofocus (PGA) algorithm
has been widely used in Spotlight Synthetic Aperture
Radar (SAR) to remove motion-induced blurs in the
images. The PGA algorithm has been proven to be a superior
autofocus method. PGA assumes a narrow beam,
which is valid for most SAR systems. However, lower altitude
SA& have large range dependencies that cannot be
ignored. A new phase estimator for PGA is introduced
and extended to allow range dependence. An ERS-1 image
of Death Valley is used in simulations comparing the
new estimator to the widely used maximum likelihood approach
and in demonstrating the range-dependent PGA
algorithm.