BISTATIC INVERSE SYNTHETIC APERTURE RADAR IMAGING

• US 20140285371A1
• Filed: 03/20/2013
• Published: 09/25/2014
• Est. Priority Date: 03/20/2013
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Abatzoglou, Theagenis J., Gonzalez, Johan E.
• Granted Patent: US 9,335,409 B2
• Time in Patent Office: Days
• US Class Current: 342/21
• CPC Class Codes: G01S 13/582 adapted for simultaneous range and velocity measurements
• CPC Class Codes: G01S 13/589 measuring the velocity vector
• CPC Class Codes: G01S 13/9058 Bistatic or multistatic SAR
• CPC Class Codes: G01S 13/9064 Inverse SAR [ISAR]
• CPC Class Codes: G01S 7/2955 Means for determining the position of the radar coordinate system for evaluating the position data of the target in another coordinate system G01S7/24 takes precedence; sighting devices adapted for indirect laying of fire F41G3/16; inertial navigation G01C21/16

Abstract

Embodiments of synthetic aperture radar systems for mapping Doppler frequency to cross-range to form bistatic inverse synthetic radar images of airborne targets.

Claims

1. A bistatic synthetic aperture radar (SAR) imaging method, the method comprising:

receiving a plurality of radar return pulses acquired by at least first and second airborne radar platforms, wherein each radar return pulse is generated in response to a corresponding transmission pulse reflected from two or more radar scattering locations on a target;

combining each radar return pulse with a sinusoid to reduce the radar return pulses to a base band frequency;

deskewing each reduced radar return pulse to remove effects of its corresponding radar transmission pulse;

estimating motion parameters of the target based on a maximum likelihood estimation (MLE) applied to the deskewed radar return pulses;

performing MLE motion correction to the deskewed radar return pulses based on the estimated motion parameters to generate motion corrected radar return pulses;

acquiring position and velocity estimates of the two or more airborne radar platforms and the one or more scattering locations on the target;

defining bistatic range and velocity vectors based on the position and velocity estimates of the first and second airborne radar platforms, the one or more scattering locations on the target, and the motion corrected radar return pulses;

defining new bistatic range and velocity vectors by redefining the bistatic range and velocity vectors in a new set of orthogonal axes;

projecting vector distance differences between the target radar scattering locations along the new set of orthogonal axes to generate new range and velocity measurements along the new set of orthogonal axes;

converting the new range and velocity measurements in order to map Doppler frequency into cross-range, measured in physical units of length; and

forming a bistatic SAR image in range and cross-range based on cross-range extent derived from the Doppler frequency mapping.

2. The method of claim 1, wherein the bistatic range and velocity vectors are defined according to:

3. The method of claim 2, wherein the new bistatic range and velocity vectors are orthogonal parameters determined in accordance with:

4. The method of claim 3, wherein the new range and velocity measurements along the new set of orthogonal axes are determined in accordance with:

Δ

r_bistatic=Δ

{right arrow over (p)}_s·

{right arrow over (p)}_bistatic

Δ

v<sub>bistatic—

new</sub>=Δ

{right arrow over (p)}_s·

{right arrow over (p)}<sub>bistatic—

vel—

new</sub>·

5. The method of claim 4, comprising using the new range and velocity measurements to define cross-range resolution Δ

R<sub>cross—

range</sub> and cross-range extent Δ

R_extent in accordance with;

6. A bistatic synthetic aperture radar (SAR) imaging system, the system comprising:

one or more processor; and

a memory, the memory including executable code representing instructions that when executed cause the system to;

receive a plurality of radar return pulses acquired by at least first and second airborne radar platforms, wherein each radar return pulse is generated in response to a corresponding transmission pulse reflected from two or more radar scattering locations on a target;

combine each radar return pulse with a sinusoid to reduce the radar return pulses to a base band frequency;

deskew each reduced radar return pulse to remove effects of its corresponding radar transmission pulse;

estimate motion parameters of the target based on a maximum likelihood estimation (MLE) applied to the deskewed radar return pulses;

perform MLE motion correction to the deskewed radar return pulses based on the estimated motion parameters to generate motion corrected radar return pulses;

acquire position and velocity estimates of the two or more airborne radar platforms and the one or more scattering locations on the target;

define bistatic range and velocity vectors based on the position and velocity estimates of the first and second airborne radar platforms, the one or more scattering locations on the target, and the motion corrected radar return pulses;

define new bistatic range and velocity vectors by redefining the bistatic range and velocity vectors in a new set of orthogonal axes;

project vector distance differences between the target radar scattering locations along the new set of orthogonal axes to generate new range and velocity measurements along the new set of orthogonal axes;

convert the new range and velocity measurements in order to map Doppler frequency into cross-range, measured in physical units of length; and

form a bistatic SAR image in range and cross-range based on cross-range extent derived from the Doppler frequency mapping.

7. The system of claim 6, wherein the bistatic range and velocity vectors are defined according to:

8. The system of claim 7, wherein the new bistatic range and velocity vectors are orthogonal parameters determined in accordance with:

9. The system of claim 8, wherein the new range and velocity measurements along the new set of orthogonal axes are determined in accordance with:

Δ

r_bistatic=−

Δ

{right arrow over (p)}_s·

{right arrow over (p)}_bistatic

Δ

v<sub>bistatic—

new</sub>=Δ

{right arrow over (p)}_s·

{right arrow over (p)}<sub>bistatic—

vel—

new</sub>·

10. The system of claim 9, wherein the memory includes executable code representing instructions that when executed cause the system to use the new range and velocity measurements to define cross-range resolution Δ

R<sub>cross—

range</sub> and cross-range extent Δ

R_extent in accordance with;