Method of correcting azimuthal position of moving targets in SAR-images

• US 6,549,160 B2
• Filed: 08/07/2001
• Issued: 04/15/2003
• Est. Priority Date: 08/09/2000
• Status: Expired due to Fees

• Current Assignee: EADS Deutschland GmbH (Airbus SE)
• Original Assignee: EADS Deutschland GmbH (Airbus SE)
• Inventors: Meyer-Hilberg, Jochen
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): ANDREA, BRIAN K
• Application Number:
  US09/922,912
• Publication Number:
  US 20020044079A1
• Time in Patent Office: 616 Days
• Field of Search: 342/25, 342/162, 342/189, 342/160
• US Class Current: 342/25.00R
• CPC Class Codes: G01S 13/9029 specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time

Abstract

The positions of moving targets in the azimuthal direction which result from the SAR processing are falsified by components of the vehicle movement in the Doppler spectrum of the received signal, so that without the implementation of additional signal processing, moving targets are imaged in the SAR image at a false azimuth position. A method of repositioning moving targets in SAR images which consist of multi-channel range/Doppler measurement data X with N_ND Doppler resolution cells, defines on the basis of the filtering coefficients of the STAP transformed into the frequency domain, a family of N_DZ pattern functions M, and determines testing functions T assigned to the measurement data. The true azimuth position of a moving target is then computed on the basis of the position of the maximum of the correlation between the testing functions and the pattern functions.

Claims

1. A method for repositioning moving targets in SAR-images comprising multi-channel range/Doppler measurement data X, with N_DZ Doppler resolution cells, said method comprising:

defining a family of N_DZ pattern functions M, based on filtering coefficients α and

β

for Space-Time Adaptive Processing, transformed into the frequency domain;

defining a testing function, based on the filtering coefficients α and

β

transformed into the frequency domain and on the multi-channel range/Doppler measurement data;

generating a correlation function K by correlating the testing function T with a selected function of the family of pattern functions M; and

computing a true azimuth position of a moving target based on the position of a maximum of the correlation function K.

2. The method according to claim 1, wherein the family of pattern functions M in the case of two-channel range/Doppler measurement data is determined corresponding to the equation

  M(k, i)=20·

log(|α

(i)·

β

(k)−

β

(i)·

α

(k)|+ε

)

wherein 1≦

k≦

N_DZ and 1≦

i≦

N_DZ.

3. The method according to claim 1, wherein the testing function T in the case of two-channel range/Doppler measurement data is determined at the point of a defined distance cell ω

and for a defined Doppler resolution cell ρ

corresponding to $T<br><br>\left(i\right)=20·<br><br>\log <br><br>\left(<br><br>\frac{a<br><br>\left(i\right)·<br><br>X_1<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)+\mathrm{\beta <br><br>}<br><br>\left(i\right)·<br><br>X_2<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)}{X_1<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)·<br><br>X_1^{*}<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)+X_2<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)·<br><br>X_2^{*}<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)}<br><br>+\mathrm{\varepsilon <br><br>}\right)$

wherein 1≦

i≦

N_DZ.

4. The method according to claim 1, wherein:

the correlation function K corresponds to a correlation of the testing function T with the selection of one from the N_DZ pattern functions M; and

that pattern function is selected for the correlation which is to be assigned to the point m for which the cross-correlation of the range/Doppler measurement data r is maximal, corresponding to |r(m)|≧

|r(i)| with 1≦

i≦

N_DZ, so that the correlation function K is generated corresponding to the equation

5. The method according to claim 1, wherein:

the correlation function K corresponds to a correlation of the testing function T with all of the N_DZ pattern functions M; and

that pattern function M which corresponds best to the testing function T corresponds to a true azimuth position of the moving target.

6. The method according to claim 1, wherein the true azimuth position φ

is computed on the basis of a position n of a maximum of the correlation function K for which K(n)≧

K(i) with 1≦

i≦

N_DZ, corresponding to the equation

7. The method according to claim 1, wherein product terms which are required for determination of the family of pattern functions M and which consist of the filtering coefficients of the STAP filter transformed into the frequency domain, are determined on the basis of a covariance matrix of the filtering coefficients and its resolvents.

8. The method according to claim 7, wherein the product terms are determined by the multiplication of the last line of the covariance matrix with the first column of its resolvents.

9. Apparatus for correcting azimuthal position of moving objects in a synthetic aperture radar image comprising multi-channel range/Doppler measurement data X with N_DZ Doppler resolution cells, said apparatus comprising:

a data processor unit programmed to process said measurement data, according to the following steps

defining a family of N_DZ pattern functions M, based on filtering coefficients α and

β

for Space-Time Adaptive Processing, transformed into the frequency domain;

defining a testing function, based on the filtering coefficients α and

β

transformed into the frequency domain and on the multi-channel range/Doppler measurement data;

generating a correlation function K by correlating the testing function T with a selected function of the family of pattern functions M; and

computing a true azimuth position of a moving target based on the position of a maximum of the correlation function K.

10. The apparatus according to claim 9, wherein the family of pattern functions M in the case of two-channel range/Doppler measurement data is determined corresponding to the equation

11. The apparatus according to claim 9, wherein the testing function T in the case of two-channel range/Doppler measurement data is determined at the point of a defined distance cell ω

and for a defined Doppler resolution cell ρ

corresponding to $T<br><br>\left(i\right)=20·<br><br>\log <br><br>\left(<br><br>\frac{a<br><br>\left(i\right)·<br><br>X_1<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)+\mathrm{\beta <br><br>}<br><br>\left(i\right)·<br><br>X_2<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)}{X_1<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)·<br><br>X_1^{*}<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)+X_2<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)·<br><br>X_2^{*}<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)}<br><br>+\mathrm{\varepsilon <br><br>}\right)$

wherein 1≦

i≦

N_DZ.

12. The apparatus according to claim 9, wherein:

the correlation function K corresponds to a correlation of the testing function T with the selection of one from the N_DZ pattern functions M; and

that pattern function is selected for the correlation which is to be assigned to the point m for which the cross-correlation of the range/Doppler measurement data r is maximal, corresponding to |r(m)|≧

|r(i)| with 1≦

i≦

a N_DZ, so that the correlation function K is generated corresponding to the equation

13. The apparatus according to claim 9, wherein:

the correlation function K corresponds to a correlation of the testing function T with all of the N_DZ pattern functions M; and

that pattern function M which corresponds best to the testing function T corresponds to a true azimuth position of the moving target.

14. The apparatus according to claim 9, wherein the true azimuth position φ

is computed on the basis of a position n of a maximum of the correlation function K for which K(n)≧

K(i) with 1≦

i≦

N_DZ, corresponding to the equation

15. The apparatus according to claim 9, wherein product terms which are required for determination of the family of pattern functions M and which consist of the filtering coefficients of the STAP filter transformed into the frequency domain, are determined on the basis of a covariance matrix of the filtering coefficients and its resolvents.

16. The apparatus according to claim 15, wherein the product terms are determined by the multiplication of the last line of the covariance matrix with the first column of its resolvents.

17. A computer readable medium encoded with a computer program for correcting azimuthal position of moving objects in a synthetic aperture radar image comprising multi-channel range/Doppler measurement data X with N_DZ Doppler resolution cells, by:

defining a family of N_DZ pattern functions M, based on filtering coefficients α and

β

for Space-Time Adaptive Processing, transformed into the frequency domain;

defining a testing function based on the filtering coefficients α and

β

transformed into the frequency domain and on the multi-channel range/Doppler measurement data;

generating a correlation function K by correlating the testing function T with a selected function of the family of pattern functions M; and

computing a true azimuth position of a moving target based on the position of a maximum of the correlation function K.

18. The method according to claim 17, wherein the family of pattern functions M in the case of two-channel range/Doppler measurement data is determined corresponding to the equation

19. The method according to claim 17, wherein the testing function T in the case of two-channel range/Doppler measurement data is determined at the point of a defined distance cell ω

and for a defined Doppler resolution cell ρ

corresponding to $T<br><br>\left(i\right)=20·<br><br>\log <br><br>\left(<br><br>\frac{a<br><br>\left(i\right)·<br><br>X_1<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)+\mathrm{\beta <br><br>}<br><br>\left(i\right)·<br><br>X_2<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)}{X_1<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)·<br><br>X_1^{*}<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)+X_2<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)·<br><br>X_2^{*}<br><br>\left(\mathrm{\omega <br><br>},\mathrm{\rho <br><br>}\right)}<br><br>+\mathrm{\varepsilon <br><br>}\right)$

wherein 1≦

i≦

N_DZ.

20. The method according to claim 17, wherein:

the correlation function K corresponds to a correlation of the testing function T with the selection of one from the N_DZ pattern functions M; and

that pattern function is selected for the correlation which is to be assigned to the point m for which the cross-correlation of the range/Doppler measurement data r is maximal, corresponding to |r(m)|≧

|r(i)| with 1≦

i≦

N_DZ, so that the correlation function K is generated corresponding to the equation