Synthetic aperture radar (SAR) data compression

• US 7,411,540 B1
• Filed: 03/10/2005
• Issued: 08/12/2008
• Est. Priority Date: 03/10/2005
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: Lopez, Norman A., Mulford, Michael T.
• Primary Examiner(s): Sotomayor; John B
• Application Number:
  US11/077,053
• Time in Patent Office: 1,251 Days
• Field of Search: 342/25.R, 342/25.A, 342/25.B, 342/25.C, 342/25.D, 342/25.E, 342/25.F, 342/159, 342/189, 342/191, 342/192, 342/196
• US Class Current: 342/25.00R
• CPC Class Codes: G01S 13/9011 with frequency domain processing of the SAR signals in azimuth G01S13/9005 takes precedence
• CPC Class Codes: G01S 13/9017 with time domain processing of the SAR signals in azimuth G01S13/9005 takes precedence

Abstract

A method of compressing phase history (PH) data includes (a) dividing PH data into multiple sub-apertures; (b) transforming the sub-apertures into multiple coarse resolution images; and (c) compressing each of the coarse resolution images. Compressing each of the coarse resolution images may include (i) selecting at least one image from the coarse resolution images to form a base image, (ii) differencing each of the coarse resolution images from the base image to form residual images, and (iii) quantizing the residual images.

Claims

1. A method of compressing phase history (PH) data comprising the steps of:

(a) dividing PH data into a plurality of sub-apertures;

(b) transforming the sub-apertures into a plurality of coarse resolution images; and

(c) compressing each of the coarse resolution images.

2. The method of claim 1 wherein

compressing each of the coarse resolution images includes:

selecting at least one image from the coarse resolution images to form a base image,

differencing each of the coarse resolution images from the base image to form residual images, and

quantizing the residual images.

3. The method of claim 2 wherein the base image is selected by performing the following steps:

(i) calculating an energy value for each of the coarse resolution images,

(ii) selecting a median energy value from the energy values calculated in step (i), and

(iii) selecting the base image as a coarse resolution image having the median energy value.

4. The method of claim 1 wherein

step (a) includes one of the following:

(i) forming non-overlapping sub-apertures, and

(ii) forming overlapping sub-apertures.

5. The method of claim 1 wherein

step (b) includes transforming the sub-apertures using a two-dimensional Fourier transform, two one-dimensional Fourier transforms, or a fast Fourier transform (FFT).

6. The method of claim 1 wherein

the phase history data contains M_FT^SAR fast time samples and N_ST^SAR slow time samples, and

the sub-aperture size is defined as an

7. The method of claim 1 wherein

the PH data is raw data or formatted data.

8. The method of claim 7 wherein

the formatted data is polar formatted data.

9. The method of claim 1 further including the step of:

prior to performing step (a), transforming complex image data from a synthetic aperture radar (SAR) into the PH data.

10. The method of claim 9 wherein

transforming the complex image data includes using an inverse FFT to form the PH data.

11. The method of claim 1 wherein

step (c) includes using both a high bit rate coder and a low bit rate coder to compress the coarse resolution images.

12. The method of claim 1 wherein

the PH data includes magnitude components and phase components.

13. The method of claim 1 wherein

compressing each of the coarse resolution images includes normalizing each of the sub-apertures, prior to the compressing step.

14. The method of claim 1 wherein

the PH data is partitioned into multiple regions, and

steps (a), (b) and (c) are performed for each of the multiple regions independently of each other region.

15. A method of forming reconstructed PH data comprising the steps of:

(a) extracting coarse resolution images from a storage device;

(b) decompressing each of the coarse resolution images to form normalized coarse resolution images;

(c) transforming each of the normalized coarse resolution images into a respective sub-aperture; and

(d) combining respective sub-apertures to form the reconstructed PH data.

16. The method of claim 15 wherein

step (c) includes using an inverse FFT to form each of the respective sub-apertures, and

step (d) includes placing the respective sub-apertures at different locations into an array to form the reconstructed PH data.

17. A system for compressing phase history (PH) data comprising

a memory for storing multiple sub-apertures of PH data, wherein each of the sub-apertures is a sub-array formed from an array of PH data,

an image formation module for transforming each of the sub-apertures into a respective coarse resolution image, and

an encoder for compressing the respective coarse resolution image.

18. The system of claim 17 wherein the encoder includes

a base image selector for selecting at least one image from the respective coarse resolution images and forming a base image,

a residual calculator for differencing each of the respective coarse resolution images from the base image and forming residual images, and

a quantizer for compressing the residual images.

19. The system of claim 18 wherein the encoder includes

a normalizer for normalization the residual images and outputting normalized residual images to the quantizer.

20. The system of claim 17 wherein

the image formation module includes at least one of a two-dimensional Fourier transform, two one-dimensional Fourier transforms, or a fast Fourier transform (FFT) for forming the respective coarse resolution images.

21. The system of claim 17 wherein

the PH data is raw data or polar formatted data.

22. The system of claim 17 wherein

the phase history data contains

23. The system of claim 17 wherein

the PH data is derived from complex image data of a SAR using an inverse FFT module.