Method and system for producing images of an object

• US 5,949,364 A
• Filed: 01/06/1998
• Issued: 09/07/1999
• Est. Priority Date: 01/06/1998
• Status: Expired due to Fees

• Current Assignee: National Aeronautics and Space Administration (Government of the United States of America)
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Garrison, James L. Jr., Katzberg, Stephen J.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US09/003,247
• Time in Patent Office: 609 Days
• Field of Search: 342/25, 342/52, 342/126, 342/357, 342/453, 342/357.01
• US Class Current: 342/25.00A
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 19/22 Multipath-related issues

Abstract

A method and system are provided to produce images of an object. A receiving station is positioned in view of a range-coded signal emitting satellite and the object. The receiving station is sensitive to direct transmission of the range-coded signal and reflections of the range-coded signal from the object. Both range from the receiving station to the object and a Doppler frequency shift history between the receiving station and the object is determined using the direct transmission and reflections of the range-coded signal. An image is formed using the two-dimensional record provided by the range and the Doppler frequency shift history.

Claims

1. A method of producing images of an object, comprising the steps of:

providing a satellite in line-of-sight of an object, said satellite being capable of transmitting a range-coded signal;

positioning a receiving station in view of said satellite and said object, said receiving station being sensitive to direct transmission of said range-coded signal from said satellite and reflections of said range-coded signal from said object;

introducing relative motion between said receiving station and said object;

determining range from said receiving station to said object using said direct transmission and said reflections;

determining a Doppler frequency shift history between said receiving station and said object using said direct transmission and said reflections; and

forming an image of said object using said range and said Doppler frequency shift history.

2. A method according to claim 1 wherein said step of positioning includes the step of positioning said object between said satellite and said receiving station.

3. A method according to claim 1 wherein said step of introducing includes the step of controlling movement of said receiver.

4. A method according to claim 1 wherein said satellite is selected from the group consisting of Global Positioning System (GPS) satellites and GLONASS satellites.

5. A method according to claim 1 wherein said step of determining said Doppler frequency shift history is accomplished using synthetic aperture radar (SAR) processing techniques.

6. A method according to claim 1 further comprising the step of storing said range and said Doppler frequency shift history.

7. A method according to claim 1 further comprising the steps of:

providing a reference code indicative of said range-coded signal transmitted from said satellite; and

correlating said reference code with each of said reflections for each of a plurality of phase shifts between said reference code and each of said reflections to generate a plurality of power outputs, wherein said step of forming uses said range, said Doppler frequency shift history and said plurality of power outputs.

8. A method according to claim 7 further comprising the steps of:

determining a location of said receiver; and

selecting said plurality of phase shifts using said location.

9. A method according to claim 7 wherein said step of correlating is performed as a serial process for each of said reflections.

10. A method according to claim 7 wherein said step of correlating is performed as a parallel process on non-overlapping portions of said plurality of phase shifts for each of said reflections.

11. A system for producing images using a range-coded signal that is transmitted toward the earth from an orbiting satellite, comprising:

receiving means positioned such that an object to be imaged is in view of said satellite and said receiving means and such that there is relative motion between said receiving means and said object, said receiving means being sensitive to a direct transmission of said range-coded signal and to reflections of said range-coded signal from said object;

processing means coupled to said receiving means for determining range from said receiving means to said object using said direct transmission and said reflections, and for determining a Doppler frequency shift history between said receiving means and said object using said direct transmission and said reflections; and

a device coupled to said processing means for forming an image of said object using said range and said Doppler frequency shift history.

12. A system as in claim 11 wherein said processing means includes a correlator for correlating a reference code indicative of said range-coded signal transmitted from said satellite with each of said reflections for each of a plurality of phase shifts between said reference code and each of said reflections, wherein a plurality of power outputs associated with each of said reflections are generated, and wherein said device for forming an image of said object uses said range, said Doppler frequency shift history and said plurality of power outputs.

13. A system as in claim 12 wherein said correlator comprises a plurality of correlator subsections, each of said correlator subsections being provided with said reference code, each of said reflections, and a non-overlapping portion of said plurality of phase shifts, wherein said plurality of correlator subsections operate in parallel to generate said plurality of power outputs.

14. A system as in claim 12 further comprising a device for predicting said plurality of phase shifts.

15. A system as in claim 14 wherein said device for predicting comprises:

a locating system positioned in proximity to said receiving means for determining a location of said receiving means relative to said satellite; and

a processor coupled to said locating system for generating predictions of values for said plurality of phase shifts based on said location.

16. A system as in claim 15 wherein said satellite is a Global Positioning System (GPS) satellite and said locating system is a GPS receiver.