High frequency phase errors in SAR imagery and implications for autofocus

The subject of this paper is the characterization of high frequency phase errors in synthetic aperture radar (SAR) imagery formed using the polar format processing approach and the implications for autofocus. A mathematical model for the phase error is reviewed which illustrates the dependency of the phase error on range wavenumber as well as azimuth wavenumber. In the case of a single sinusoidal phase error, it is shown that the resulting paired echoes have a characteristic two-dimensional (2D) appearance. This implies that for sufficiently high phase error frequencies the associated autofocus problem is 2D, that is the phase error is a function of range and azimuth wavenumbers. Radars operating at long wavelengths and fine resolution, such as a 1 meter resolution L-band system, are the most likely candidates to produce imagery having 2D phase error