Method and system for mutual coherent synthetic aperture radiometry

• US 6,861,978 B2
• Filed: 02/14/2003
• Issued: 03/01/2005
• Est. Priority Date: 04/12/2002
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Lam, Larry K.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US10/367,621
• Publication Number:
  US 20040004569A1
• Time in Patent Office: 746 Days
• Field of Search: 342/351, 342/430, 342/418, 342/189, 342/25, 250/250
• US Class Current: 342/351
• CPC Class Codes: G01S 13/904 SAR modes
• CPC Class Codes: G01S 3/02 using radio waves

Abstract

Method and system for synthetic aperture radiometry not limited by the Van Cittert-Zernike theorem and the quasi-monochromatic assumption. A radiometer system (300) for imaging the emissions from a distribution of incoherent emission sources located within a target area comprising a first antenna (322) configured to receive a first signal (326) emitted primarily from a target area, and a second antenna (324) configured to receive a second signal (327) emitted primarily from the target area. The first and second antennas may be located at approximately the same distance from the target area (310) or at substantially different distances from the target area (310). The radiometer system (300) is configured to allow the second antenna (324) to move faster than the first antenna (322) with respect to the target area (310), with the second antenna (324) moving along a pre-determined trajectory corresponding to a synthetic aperture (430). A cross correlation receiver (330) computes a plurality of cross correlation functions as based on all relevant relative time delays between the first signal (326) and the second signal (327). The image processor (340) converts computed correlation data (332) into a plurality of complex valued radial down range profiles of the target area and further computes an image of the target area based on synthetic aperture image processing principle.

Claims

1. A system for imaging a target, the system comprising:

a first antenna configured to receive from an imaging target a first signal occupying a first bandwidth including substantially more than one frequency;

a second antenna configured to receive from the imaging target a second signal occupying a second bandwidth including substantially more than one frequency and to perform a spatial movement relative to the first antenna, the spatial movement being associated with a synthetic aperture;

a cross correlation receiver coupled to the first antenna and the second antenna, the cross correlation receiver configured to;

process information associated with the first signal and the second signal;

determine a cross correlation function based on at least information associated with the first signal and the second signal;

wherein the cross correlation function is dependent upon at least a time interval between a first time when the first antenna receiving the first signal and a second time when the second antenna receiving the second signal;

wherein the cross correlation function is associated with the synthetic aperture;

a processing system coupled to the cross correlation receiver and configured to;

determine a radial down range profile of the imaging target based on at least information associated with the cross correlation function;

perform a phase compensation to the radial down range profile;

form an image of the imaging target based on at least information associated with the phase-compensated radial down range profile;

wherein the form an image of the imaging target uses at least an synthetic aperture imaging algorithm.

2. The system of claim 1 wherein the determine a cross correlation function comprises perform a far field approximation and determine the cross correlation function based on at least information associated with the far field approximation.

3. The system of claim 2 wherein the determine a cross correlation function further comprises determine the cross correlation function for a plurality of time delays, the plurality of time delays being associated with the first signal and the second signal and including the time interval.

4. The system of claim 2 wherein the form an image of the imaging target comprises determine a cross-range profile of the imaging target using at least the synthetic aperture imaging algorithm.

5. The system of claim 4 wherein the cross correlation receiver is further configured to compensate for a Doppler frequency shift between the first signal and the second signal before computing the cross correlation function related to the first signal and the second signal, the Doppler frequency shift being associated with the spatial movement of the first antenna relative to the second antenna.

6. The system of claim 5 wherein the synthetic aperture is associated with a continuous size in response to the spatial movement of the first antenna relative to the second antenna.

7. The system of claim 6 is free from any antenna in addition to the first antenna and the second antenna.

8. The system of claim 6 wherein the processing system is further configured to

transform a plurality of time delay profiles into a plurality of radial down range profiles, the plurality of radial down range profiles including the radial down range profile;

align the centroid of each of the plurality of radial down range profiles;

perform a plurality of phase compensations to the plurality of centroid aligned radial down range profiles, the plurality of phase compensations including the phase compensation;

form the image of the imaging target based on at least information associated with the plurality of phase compensated and aligned radial down range profiles.

9. The system of claim 8 wherein the processing system comprises:

a plurality of analog to digital converters;

a plurality of baseband converters coupled to the plurality of analog to digital converters;

a plurality of digital tapped delay line circuits coupled to the plurality of baseband converters;

a plurality of correlation modules coupled to the plurality of digital tapped delay line circuits;

a memory system coupled to the plurality of correlation modules.

10. The system of claim 9 wherein the memory system is configured to store information associated with the plurality of radial down range profiles for the imaging target.

11. The system of claim 10 wherein the second antenna moves faster than the first antenna with respect to the imaging target.

12. The system of claim 11 wherein the first antenna and the second antenna are located at substantially the same distance from the imaging target and configured to cause the second antenna to move along a predetermined trajectory, the predetermined trajectory defining the synthetic aperture suitable to support the synthetic aperture imaging algorithm.

13. The system of claim 11 wherein the first antenna and the second antenna are located at substantially different distances from the imaging target and configured to cause the second antenna to move along a predetermined trajectory, the predetermined trajectory defining the synthetic aperture suitable to support the synthetic aperture imaging algorithm.

14. The system of claim 10 wherein the cross correlation receiver is configured to process at least two channels of signals, the at least two channels of signals occupying substantially the same frequency band, the same frequency band having a bandwidth substantially wider than a bandwidth of signals collected in accordance with the Van Cittert-Zernike theorem for collecting interferometric Γ

(U,V) data for filling a (U,V) plane.

15. The system of claim 8 wherein the first bandwidth is larger than 50 MHz, and the second bandwidth is larger than 50 MHz.

16. The system of claim 15 wherein the first bandwidth is larger than 300 MHz, and the second bandwidth is larger than 300 MHz.

17. The system of claim 16 wherein the first bandwidth is larger than 1 GHz, and the second bandwidth is larger than 1 GHz.

18. The system of claim 8 wherein the first bandwidth and the second bandwidth fall within the microwave range.

19. The system of claim 18 wherein the image for the imaging target has a resolution of one foot.

20. The system of claim 8 wherein the first antenna and the second antenna perform passive microwave remote sensing.

21. The system of claim 8 wherein the first antenna and the second antenna perform a geological survey.

22. The system of claim 8 wherein the first antenna and the second antenna perform passive ground mobile target indication.

23. The system of claim 8 wherein the cross correlation function is a mutual coherence function.

24. The system of claim 8 wherein the imaging target is located on the Earth.

25. The system of claim 24 wherein the first antenna and the second antenna are located in the air or in space.

26. The system of claim 8 wherein the first antenna and the second antenna are placed on a first aircraft and a second aircraft respectively.

27. The system of claim 8 wherein the first antenna and the second antenna are placed on a first spacecraft and a second spacecraft respectively.

28. The system of claim 8 wherein the first antenna and the second antenna are placed on a spacecraft and an aircraft respectively.

29. The system of claim 8 wherein an angle between a first line connecting the first antenna and the imaging target and a second line connecting the second antenna and the imaging target ranges from 30 to 160 degrees.

30. The system of claim 29 wherein the angels ranges from 60 to 90 degrees.

31. The system of claim 8 wherein an angel between a first line connecting the first antenna and the imaging target and a second line connecting the second antenna and the imaging target ranges from 20 to 120 degrees.

32. The system of claim 31 wherein the angels ranges from 20 to 60 degrees.