Method of correcting range migration in image generation in synthetic aperture radar

Claim 1

A method of correcting range migration in image generation in synthetic aperture radar SAR for eliminating the entire range migration, which in the range-Doppler domain is described by ##EQU20## wherein Δτ is the desired echo time shift, r the minimum distance of a point from the radar and f the azimuth (Doppler) frequency, or for eliminating a residual range migration, which is left by a focussing means, is described by ##EQU21## wherein τ' is any desired reference echo time, and for carrying out a Stolt interpolation respectively; before performing a range compression, acquire SAR raw data which is to be transformed, in an azimuth FFT unit, to the range-Doppler domain; thereafter multiply, in a first multiplying unit, said data transformed to the range-Doppler domain by a two-functional phase function exp {j·π·k·a(f)·(τ-τ').sup.2 } wherein k is the frequency modulation rate of a chirp pulse transmitted by the radar and τ the echo travelling time; performing range Fourier transformation on the data from said first multiplying unit; a range compression is carried out in a second multiplying unit by multiplying an output of said range Fourier transformation with a modified range transfer function ##EQU22## wherein υ is the range frequency corresponding to the echo travelling time τ; using an inverse range FFT unit, transform output data of said second multiplying unit back to the range-Doppler domain; and correct phase error, by using a third multiplying unit, to multiply output data from said inverse range FFT unit with a function exp {-j·π·a(f)·(l+a(f))·k·(.tau.-τ').sup.2 }.

Claim 2

A method of correcting range migration in image generation in synthetic aperture radar SAR for eliminating the entire range migration, which in the range-Doppler domain is described by ##EQU20## wherein Δτ is the desired echo time shift, r the minimum distance of a point from the radar and f the azimuth (Doppler) frequency, or for eliminating a residual range migration, which is left by a focussing means, is described by ##EQU21## wherein τ' is any desired reference echo time, and for carrying out a Stolt interpolation respectively; before performing a range compression, acquire SAR raw data which is to be transformed, in an azimuth FFT unit, to the range-Doppler domain; thereafter multiply, in a first multiplying unit, said data transformed to the range-Doppler domain by a two-functional phase function exp {j·π·k·a(f)·(τ-τ').sup.2 } wherein k is the frequency modulation rate of a chirp pulse transmitted by the radar and τ the echo travelling time; performing range Fourier transformation on the data from said first multiplying unit; a range compression is carried out in a second multiplying unit by multiplying an output of said range Fourier transformation with a modified range transfer function ##EQU22## wherein υ is the range frequency corresponding to the echo travelling time τ; using an inverse range FFT unit, transform output data of said second multiplying unit back to the range-Doppler domain; and correct phase error, by using a third multiplying unit, to multiply output data from said inverse range FFT unit with a function exp {-j·π·a(f)·(l+a(f))·k·(.tau.-τ').sup.2 }.