1. A method for focusing an image, the method comprising: receiving an image comprising data collected from a synthetic aperture radar system; selecting a number of initial subpatches from the image, the number of initial subpatches not covering all of the image; estimating a phase error for each of the initial subpatches; creating a spatial model for spatial variation in phase error for the image based on the phase error for the initial subpatches, creating the model including determining a number of subpatches and the size of the number of subpatches, creating the spatial model including modeling a spatial version of the phase error for each of the initial subpatches using the phase error for the number of initial subpatches to form the spatial model; dividing the image into the number of subpatches based on the spatial model so as to cover the entire image with the number of subpatches; generating a number of coefficients for a polynomial for the phase error for each initial subpatch in the number of initial subpatches to form a number of sets of coefficients; fitting values for the number of sets of coefficients to form the spatial model; applying phase correction to each of the number of subpatches to form a number of focused subpatches, the applying phase correction including performing an optimization to identify an array of coefficients for a polynomial representing a phase correction in a manner that minimizes an entropy value generated by an entropy calculation for the image for each of the number of subpatches; and merging the number of focused subpatches to form a focused image.