Two-Dimensional Autofocus Technique Based on Spatial Frequency Domain Fragmentation.

Existing two-dimensional (2-D) autofocus algorithms, exploiting the known structure of 2-D phase error, lack the error estimation accuracy in the case of a low signal-tonoise ratio (SNR) due to the non-exhaustive use of the echo signal. In this paper, we propose a novel 2-D autofocus algorithm, thoroughly utilizing all the available data and therefore achieving superior estimation performance. Via analytical study, we show that the partial derivative of the 2-D error with respect to the azimuth frequency is approximable as a function of single argument, after appropriate change of variable.