ENHANCED RADAR RANGE RESOLUTION

• US 20140218231A1
• Filed: 11/29/2012
• Published: 08/07/2014
• Est. Priority Date: 11/29/2012
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Abatzoglou, Theagenis J., Gonzalez, Johan E., McWilliams, Joel K., Samaniego, Raymond, Yeary, Mark B., Santiago, Enrique A.
• Granted Patent: US 9,103,918 B2
• Time in Patent Office: Days
• US Class Current: 342/25.A
• CPC Class Codes: G01S 13/9004 SAR image acquisition techniques
• CPC Class Codes: G01S 7/28 Details of pulse systems

Abstract

A synthetic aperture radar imaging method that combines each radar return pulse with a sinusoid to reduce the radar return pulses to a baseband frequency and deskew each radar return pulse. It includes determining a maximum likelihood estimate (MLE) of residual motion parameters for a dominant scatterer on the ground relative to the airborne radar and correcting for errors in inertial navigation system measurements based on the MLE residual motion parameters. It includes convolving each radar return pulse with its corresponding radar transmission pulse to generate a range compressed image for each radar return pulse and generating a sub-band range profile image for each radar return pulse and its corresponding radar transmission pulse based on the corresponding range compressed image that has been corrected for residual motion. Performing bandwidth extrapolation on each sub-band and subsequently combining the three bands to produce an enhanced resolution image without grating lobes.

Claims

1. A synthetic aperture radar imaging method, comprising:

receiving a plurality of radar return pulses acquired by an airborne radar, wherein each radar return pulse is generated in response to a corresponding radar transmission pulse reflected from objects within a region of interest on the ground;

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

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

determining a maximum likelihood estimate (MLE) of residual motion parameters for a dominant scatterer on the ground relative to the airborne radar, based on the deskewed radar return pulses;

correcting for errors in inertial navigation system measurements based on the MLE residual motion parameters;

convolving each radar return pulse with its corresponding radar transmission pulse to generate a range compressed image for each radar return pulse;

generating an original sub-band range profile image for each radar return pulse and its corresponding radar transmission pulse based on the corresponding range compressed image that has been corrected for residual motion; and

combining the sub-band range profile images to obtain a combined range profile image.

2. The method of claim 1, wherein the combined range profile image has a higher resolution than each of the original sub-band range profile images.

3. The method of claim 1, wherein each sub-band range profile image is generated by extrapolating the sub-band to a common frequency band larger than each of the sub-band range profile images and forming a composite image using and image formation method.

4. The method of claim 3, wherein the image formation method is selected from the group consisting of backprojection or polar formatting.

5. The method of claim 1, wherein the radar transmission pulses are disjoint radio frequency bands.

6. The method of claim 5, wherein two or more of the radar transmission pulses are partially overlapping radio frequency bands.

7. The method of claim 6, wherein the partially overlapping radio frequency bands reduces side lobe effects in the combined range profile image.

8. The method of claim 1, wherein convolving each radar return pulse with its corresponding radar transmission pulse to generate a range compressed image for each radar return pulse includes implementing a matched filter to generate the range compressed image for each radar return pulse.

9. The method of claim 1, wherein generating an original sub-band range profile image for each radar return pulse and its corresponding radar transmission pulse includes applying a calibration phasor to each sub-band range profile image to match the phase at the boundaries of the rsub-band range profile images.

10. A synthetic aperture radar imaging system;

comprising;

a processor; and

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

receive a plurality of radar return pulses from an airborne radar, wherein each radar return pulse is generated in response to a corresponding radar transmission pulse reflected from objects within a region of interest on the ground;

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

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

determine a maximum likelihood estimate (MLE) of residual motion parameters for a dominant scatterer on the ground relative to the airborne radar, based on the deskewed radar return pulses;

correct for errors in inertial navigation system measurements based on the MLE residual motion parameters;

convolve each radar return pulse with its corresponding radar transmission pulse to generate a range compressed image for each radar return pulse;

generate an original sub-band range profile image for each radar return pulse and its corresponding radar transmission pulse based on the corresponding range compressed image that has been corrected for residual motion; and

combine the sub-band range profile images to obtain a combined range profile image.

11. The system of claim 10, wherein the memory includes code representing instructions that when executed cause the processor to generate each sub-band range profile image by extrapolating the sub-band to a common frequency band larger than each of the sub-band range profile images and forming a composite image using an image formation method.

12. The system of claim 11, wherein the image formation method is selected from the group consisting of back projection or polar formatting.

13. The system of claim 10, wherein the memory includes code representing instructions that when executed cause the processor to convolve each radar return pulse with its corresponding radar transmission pulse to generate a range compressed image for each radar return pulse by implementing a matched filter to generate the range compressed image for each radar return pulse.

14. The system of claim 10, comprising a transmitter to transmit the radar transmission pulses towards the objects within a region of interest on the ground and a receiver to receive the radar return pulses.

15. The system of claim 10, wherein generating an original sub-band range profile image for each radar return pulse and its corresponding radar transmission pulse includes applying a calibration phasor to each sub-band range profile image to match the phase at the boundaries of the rsub-band range profile images.