Patent ID: 7145496

Claim:
A radar on a moving platform for generating a focused synthetic aperture image of a scene from a sequence of periodic pulse returns from said scene, said pulse returns approximately motion compensated for the motion of said moving platform with respect to said scene, said radar comprising: analog to digital converter for converting said pulse returns into a digital stream; a computer for: receiving said digital stream; approximately phase aligning said pulse returns from said scene with respect to the motion of said moving platform to generate an initial synthetic aperture image, said initial synthetic aperture image formed from a plurality of pixel intensities z n (x, y) within a x,y extent of said initial synthetic aperture image; selecting targets from said initial synthetic aperture image using a sliding window, computing a first entropy for said targets, and sorting said targets using said first entropy to obtain a target list having target elements; concatenating said target elements to form a data matrix compatible in a dimension with a Fast Fourier Transform; iteratively computing a phase correction to be applied to said initial synthetic aperture image using an inner loop, a mid loop and an outer loop, said phase correction expressed using an orthogonal polynomial having a plurality n consecutive terms a n , a 2 denoting a quadratic term, and a N denoting a last order term of said consecutive terms of said orthogonal polynomial; said outer loop, using an L index, calculating an outer loop E L (a 2 ) entropy for said quadratic term and an outer loop E L (a N ) entropy for said last order term, iterations within said outer loop continuing until E L (a 2 )−E L (a N ) is less than an outer loop tolerance; said mid loop, using said n as an index, calculating a mid loop entropy E L (a n−1 ) and a mid loop entropy E L (a n ), for two of said consecutive order terms, iterations within said mid loop continuing until E L (a n−1 )−E L (a n ) is less than a mid loop tolerance; said inner loop, using said n as an index, calculating an inner loop entropy E L (a n,m−1 ) and an inner loop entropy E L (a n,m ) said inner loop iteration continuing until E L (a n,m−1 )−E L (a n,m ) is less than an inner loop tolerance; applying said phase correction to said initial synthetic aperture image to obtain a focused synthetic aperture image.