Fast and slow time scale clutter cancellation

• US 7,006,034 B1
• Filed: 03/10/2005
• Issued: 02/28/2006
• Est. Priority Date: 03/10/2005
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Krikorian, Mary, Rosen, Robert A., Krikorian, Kapriel V.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US11/077,093
• Time in Patent Office: 355 Days
• Field of Search: 342 25 R- 25 F, 342 89-103, 342159-164, 342/175, 342192-197
• US Class Current: 342/159
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• CPC Class Codes: G01S 13/9029 specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time

Abstract

Target detection in the presence of non stationary clutter is improved by a radar receiver on a moving platform for detecting a target using a plurality of short coherent arrays and a plurality of long coherent arrays synthesized from the short coherent arrays overlapping the target. The target is obscured by slow scale clutter and fast scale clutter in the vicinity of the target. The radar receiver has a plurality of subapertures overlapping to acquire radar returns reflected from the target during the arrays, an analog to digital converter for each of the subapertures to convert the radar returns into digital radar returns for a plurality of range bins covering the target, the slow scale clutter and the fast scale clutter; and a digital computer for performing steps of SAR image creation, further enhanced by thresholding short array magnitude data, computing a time domain component of threshold filters using the thresholded short array magnitude data then coherently subtracting the time domain component of threshold filters from the short arrays, and using the result to synthesize long coherent arrays. A Space Time Adaptive Algorithm (STAP) is applied to the long coherent arrays thus obtained to suppress slow and stationary clutter. The short coherent arrays are between 10 and 400 milliseconds long. The long coherent arrays are between 400 and 4000 milliseconds long.

Claims

1. A radar receiver on a moving platform for detecting a target using a plurality of short coherent arrays and a plurality of long coherent arrays synthesized from said short coherent arrays, said plurality of short coherent arrays and said plurality of long coherent arrays overlapping over said target, said target obscured by a slow scale clutter and a fast scale clutter in the vicinity of said target, said radar receiver comprising:

a plurality of subapertures, each of said subapertures having receive patterns, said receive patterns overlapping to acquire radar returns reflected from said target during said plurality of short coherent arrays, said target obscured by said slow scale clutter and said fast scale clutter during said plurality of short coherent arrays;

an analog to digital converter for each of said subapertures to convert said radar returns into digital radar returns for a plurality of range bins, said range bins covering said target and said slow scale clutter and fast scale clutter during said plurality of short coherent arrays;

a digital computer for performing the steps of;

motion compensating said digital radar returns derived from each of said plurality of subapertures during said plurality of short coherent arrays for said plurality of range bins, with respect to said target, to obtain a plurality of short array focused data of said target obscured by said slow scale clutter and said fast scale clutter, for each of said subapertures;

integrating said short array focused data for each of said subapertures over said plurality of short array focused data to obtain short array integrated data for each range bin of said plurality of range bins;

computing magnitude of Doppler filters for each range bin of said plurality of range bins from said short array integrated data to obtain short array magnitude data;

comparing said short array magnitude data with a threshold for each range bin of said plurality of range bins, and setting said short array magnitude data for said range bins for each range bin of said plurality of range bins below said threshold to zero to obtain thresholded data;

computing a time domain component of threshold filters using said thresholded data for each range bin of said plurality of range bins;

coherently subtracting said time domain component of threshold filters from said short array integrated data to obtain a fast scale clutter corrected data.

2. A radar receiver as described in claim 1 wherein said fast scale clutter corrected data is synthesized to form said long coherent arrays to obtain fast scale corrected data.

3. A radar receiver as described in claim 2 wherein a Space Time Adaptive Algorithm (STAP) is applied to compressed data extracted from said fast scale corrected data.

4. A radar receiver as described in claim 3 wherein said threshold is computed using a short array variance of said short array magnitude data.

5. A radar receiver as described in claim 4 wherein said fast scale clutter corrected data is processed using acceleration matched filtering for use in said Space Time Adaptive Algorithm (STAP).

6. A radar receiver as described in claim 5 wherein said short coherent arrays are between 10 and 400 milliseconds long.

7. A radar receiver as described in claim 6 wherein said long coherent arrays synthesized from a plurality of fast scale clutter corrected data are between 400 and 4000 milliseconds long.

8. A method for operating a radar receiver on a moving platform for detecting a target using a plurality of short coherent arrays and a plurality of long coherent arrays synthesized from said short coherent arrays, said plurality of short coherent arrays and said plurality of long coherent arrays overlapping over said target, said target obscured by a slow scale clutter and a fast scale clutter in the vicinity of said target, said method comprising the steps of:

overlapping receive patterns of a plurality of subapertures, to acquire radar returns reflected from said target during said plurality of short coherent arrays, said target obscured by said slow scale clutter and said fast scale clutter during said plurality of short coherent arrays;

converting said radar returns for each of said subapertures into digital radar returns for a plurality of range bins, said range bins covering said target and said slow scale clutter and fast scale clutter during said plurality of short coherent arrays;

motion compensating said digital radar returns derived from each of said plurality of subapertures during said plurality of short coherent arrays for said plurality of range bins, with respect to said target, to obtain a plurality of short array focused data of said target obscured by said slow scale clutter and said fast scale clutter, for each of said subapertures;

integrating said short array focused data for each of said subapertures over said plurality of short array focused data to obtain short array integrated data for each range bin of said plurality of range bins;

computing magnitude of Doppler filters for each range bin of said plurality of range bins from said short array integrated data to obtain short array magnitude data;

comparing said short array magnitude data with a threshold for each range bin of said plurality of range bins, and setting said short array magnitude data for said range bins for each range bin of said plurality of range bins below said threshold to zero to obtain thresholded data;

computing a time domain component of threshold filters using said thresholded data for each range bin of said plurality of range bins;

coherently subtracting said time domain component of threshold filters from said short array integrated data to obtain a fast scale clutter corrected data.

9. A method as described in claim 8 wherein said fast scale clutter corrected data is synthesized to form said long coherent arrays to obtain fast scale corrected data.

10. A method as described in claim 9 wherein a Space Time Adaptive Algorithm (STAP) is applied to compressed data extracted from said fast scale corrected data.

11. A method as described in claim 10 wherein said threshold is computed using a short array variance of said short array magnitude data.

12. A method as described in claim 11 wherein said fast scale corrected data is processed using acceleration matched filtering for use in said Space Time Adaptive Algorithm (STAP).

13. A method as described in claim 12 wherein said short coherent arrays are between 10 and 400 milliseconds long.

14. A method as described in claim 13 wherein said long coherent arrays synthesized from a plurality of fast scale clutter corrected data are between 400 and 4000 milliseconds long.