Patent ID: 6222933
Filing Date: 2001-04-24
Classification: G01S

Abstract:
A method of processing two-dimensional spotlight SAR raw data into image data, comprising sequential steps of:(3.1) dividing the spotlight SAR raw data into azimuth sub-aperture data;(3.2) transforming the sub-aperture data, via short azimuth FFTS, into azimuthal frequency data, whereby the raw data comprises two-dimensional time data;(3.3, 3.4) multiplying the two-dimensional data by a frequency-scaling function H.sub.f (f.sub.a, t.sub.r ; r.sub.o) defined by ##EQU11##whereinf.sub.a is azimuth frequency, t.sub.r is range time, r.sub.0 is a shortest distance from a target, k.sub.r is a modulation rate of the transmitted pulses in the range, r.sub.ref is a reference range, f.sub.r is a range frequency, c.sub.0 is the speed of light, .lambda. is wavelength, and wherein .beta. is given by ##EQU12##where V is speed,whereby a secondary range compression of the two-dimensional data is performed;(3.5) transforming the two-dimensional data, via short range FFTs, into two-dimensional frequency data (azimuthal and range frequency domain);(3.6, 3.7) multiplying the two-dimensional frequency data by a residual-video-phase correction function H.sub.RVP given by ##EQU13##(3.8) transforming the two-dimensional frequency data, via short range IFFTs, back into range time/azimuthal frequency domain;(3.9) multiplying the two-dimensional data by an inverse frequency-scaling function H.sub.if given by ##EQU14##whereby a block shift is performed;(3.11) transforming the two-dimensional data, via long range FFTs, into two-dimensional frequency domain;multiplying the two-dimensional frequency data by the phase-correction function H.sub.koor given by ##EQU15##(3.15) subsequently multiplying the two-dimensional frequency data by an azimuth-scaling function H.sub.a (f.sub.a, f.sub.r) given by ##EQU16##wherein k.sub.a,scl is a scaling Doppler rate;(3.16) transforming the two-dimensional frequency data, via short azimuth FFTs, into the range frequency/azimuthal time domain;(3.17) re-assembling the azimuth sub-apertures;(3.18, 3.19) multiplying the two-dimensional data of the azimuth sub-apertures by a de-ramping function H.sub.der (t.sub.a) given byH.sub.der (t.sub.a)=exp[j.multidot..pi..multidot.k.sub.a,scl.multidot.t.sub.a.sup.2 ] (13)wherein t.sub.a is a time in the azimuth direction, to obtain de-ramped data; and(3.20) transforming the de-ramped data, via long azimuth FFTs, into the image data.