System and method for iterative fourier side lobe reduction

• US 8,665,132 B2
• Filed: 03/11/2011
• Issued: 03/04/2014
• Est. Priority Date: 12/10/2008
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Ranney, Kenneth I., Nguyen, Lam Huy, Sichina, Jeffrey P.
• Primary Examiner(s): Brainard, Timothy A
• Application Number:
  US13/046,250
• Publication Number:
  US 20110163912A1
• Time in Patent Office: 1,089 Days
• Field of Search: 342/25, 342/179, 382/276
• US Class Current: 342/25.R
• CPC Class Codes: G01S 13/9017 with time domain processing of the SAR signals in azimuth G01S13/9005 takes precedence
• CPC Class Codes: G01S 13/9089 SAR having an irregular aperture
• CPC Class Codes: G01S 7/414 Discriminating targets with respect to background clutter

Abstract

A method and system for generating images from projection data comprising: at least one processor for processing input data, the input data comprising positional data and image data, the image data comprising frequency data for a pre-determined number k frequencies the at least one processor operating to: a) set the frequency data to zero for a predetermined percentage of the k frequencies to form modified frequency data; b) form a preliminary image comprising an array of retained pixel values based upon first positional data and the modified frequency data; c) set the frequency data to zero for a predetermined percentage of the k frequencies to form modified frequency data; d) form a modified image comprising an array of pixels based upon the positional data and the modified frequency data; e) compare the retained array of pixel values to the pixel values of the modified image formed at step (d); f) retain the minimum pixel value at each pixel location to form an image comprising minimum pixel values; g) repeat steps (c) through (f) for L iterations each time retaining an array of pixel values; h) output the image of retained pixel values.

Claims

1. A computer implemented method for generating images comprising:

inputting from at least one data receiving element data representing positional and radar data;

each of the positional data forming a positional record in an array of positional records;

each of the radar data comprising a first number of radar data points in the frequency domain,

forming an image comprising an array of pixel values comprising;

a) randomly setting a percentage of the first number of radar data points to zero;

b) transforming the first number of radar data points into time domain projection data;

c) forming an image by processing the projection data utilizing an imaging subsystem that combines the positional and projection data to form the SAR imagery utilizing one of a back-projection algorithm or range migration algorithm;

d) forming the complete aperture A₀ for SAR image formation comprising combining the projection data, the coordinates of the receiver, and the coordinates of the transmitter for each positional record;

e) forming an imaging grid comprising M image pixels wherein each pixel in the imaging grid is located at coordinate (x_P(i),y_P(i),z_P(i));

f) saving the pixel values for each of the M image pixels into a composite image grid;

g) randomly setting a percentage of the first number of radar data points to zero;

h) transforming the first number of radar data points into time domain projection data;

i) forming an image by processing the projection data utilizing an imaging subsystem that combines the positional and projection data to form the SAR imagery utilizing one of a back-projection algorithm or range migration algorithm;

j) forming the complete aperture A₀ for SAR image formation comprising combining the projection data, the coordinates of the receiver, and the coordinates of the transmitter for each positional record;

k) forming an imaging grid comprising M image pixels wherein each pixel in the imaging grid is located at coordinate (x_P(i),y_P(i),z_P(i));

I) comparing the pixel values of the imaging grid to the corresponding pixel values of the composite image;

m) replacing the pixel values in the composite image grid if the pixel value is less in the imaging grid than the corresponding pixel value of the composite image grid to form a new composite image grid;

n) repeating the steps g) through m) for a predetermined number of iterations;

whereby the composite image grid is outputted with reduced sidelobes and noise.

2. The method of claim 1 wherein the step of inputting from at least one data receiving element comprises inputting radar data in either the frequency domain or in the time domain, and wherein if the radar data is in the time domain it is converted first to the frequency domain before the step of randomly removing a percentage of the first number of radar data points.

3. The method of claim 1 wherein the percentage of the first number of radar data points set to zero is in the range of approximately twenty to fifty per cent.

4. The method of claim 3 wherein each radar data point comprises one frequency location and wherein each time a set of radar data points are set to zero the radar data points set to zero are not located in the same set of frequency locations.

5. The method of claim 1 wherein each radar data point is one frequency location and wherein the step of selecting and removing radar data comprises arbitrarily setting a predetermined percentage of radar data to a zero value each time from randomly selected frequency locations within the array.

6. The method of claim 1, further comprising the step of processing return radar signals using a signal processing subsystem, the signal processing subsystem comprising at least one signal processing algorithm performed to suppress unwanted noise from the returned radar data.

7. The method of claim 1 wherein the array of positional records comprises a predetermined number k positional records;

the first positional record and the associated radar data represent the positional information and the recorded data obtained during the first increment;

the k^th positional record in the array and the associated radar data represent the combined positional information and recorded data obtained by the at least one data receiving element during the k^th increment;

where k is a number greater than 1.

8. A system for generating images from projection data comprising:

at least one processor for processing input data, the input data comprising positional data and image data, the image data comprising frequency data for a pre-determined number k frequencies

the at least one processor operating to;

a) set the frequency data to zero for a predetermined percentage of the k frequencies to form modified frequency data;

b) form a preliminary image comprising an array of retained pixel values based upon first positional data and the modified frequency data;

c) set the frequency data to zero for a predetermined percentage of the k frequencies to form modified frequency data;

d) form a modified image comprising an array of pixels based upon the positional data and the modified frequency data;

e) compare the retained array of pixel values to the pixel values of the modified image formed at step (d);

f) retain the minimum pixel value at each pixel location to form an image comprising minimum pixel values;

g) repeat steps (c) through (f) for L iterations each time retaining an array of pixel values;

h) output the image of retained pixel values.

9. The system of claim 8 wherein at step (c) the frequency data is set to zero for a predetermined percentage of k frequencies by randomly selecting which of the k frequencies will contain zero values.

10. The system of claim 8 wherein the number of iterations L is within the range of 10 to 1000.

11. The system of claim 8 wherein the projection data comprises radar data.

12. The system of claim 8 wherein the projection data comprises Synchronous Impulse Reconstruction (SIRE) radar data.

13. The system of claim 8 wherein the number of iterations L is within the range of 20 to 150.

14. A system for generating an image from projection data comprising:

at least one processor for processing input data, the input data comprising positional data and image data, the image data comprising frequency data for a pre-determined number of frequency values;

the at least one processor operating to perform minimizing operations on the pixel locations of the image by;

a) creating a plurality of frequency data arrays by setting the frequency data to zero for a predetermined percentage of the frequency values to form modified frequency array data;

the frequency data eliminated being different for each preliminary image;

b) forming a plurality of modified preliminary images, each modified preliminary image comprising an array of pixels based upon the positional data and the modified frequency array data;

c) comparing all the retained pixel values at each pixel location in the preliminary images, and retaining the minimum pixel value at each pixel location to form an image comprising minimum pixel values;

d) output the image of minimum pixel values.

15. The system of claim 14 wherein the setting of the frequency data to zero for a predetermined percentage of the frequency values is performed by randomly selecting which of the frequency values will contain zero values.

16. The system of claim 14 wherein the number of modified preliminary images is within the range of 10 to 1000.

17. The system of claim 14 wherein the projection data comprises radar data.

18. The system of claim 14 wherein the projection data comprises Synchronous Impulse Reconstruction (SIRE) radar data.

19. The system of claim 14 wherein the number of modified preliminary images is within the range of 20 to 150.