SAR autofocus for ground penetration radar

• US 9,041,585 B2
• Filed: 01/10/2012
• Issued: 05/26/2015
• Est. Priority Date: 01/10/2012
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Jin, Michael Y.
• Primary Examiner(s): Sotomayor, John B
• Assistant Examiner(s): WINDRICH, MARCUS E
• Application Number:
  US13/347,548
• Publication Number:
  US 20140015710A1
• Time in Patent Office: 1,232 Days
• Field of Search: 342/22, 342 25 R- 25 F
• US Class Current: 342/25.A
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals
• CPC Class Codes: G01S 13/904 SAR modes

Abstract

A method of synthetic aperture radar autofocus for ground penetration radar. The method includes transmitting a signal via an antenna; receiving a reflected signal comprising a plurality of image blocks via the antenna; reading each image block from the reflected signal via a processor; locating prominent targets in each image block via the processor; estimating ground penetration phase error via the processor in each image block via phase error inputs including pulling range and quantization level by generating a 1D phase error and converting the 1D phase error into a 2D phase error of an image spectra; refocusing each image block according to estimated ground penetration phase error for that image block via the processor; and forming an image mosaic comprising each refocused image block via the processor.

Claims

1. A method of synthetic aperture radar autofocus for ground penetration radar, the method comprising:

transmitting a signal via an antenna;

receiving a reflected signal comprising an image via the antenna;

dividing the image into a plurality of image blocks, each image block to be refocused separately;

reading each image block from the image via a processor;

locating prominent targets in each image block via the processor;

estimating ground penetration phase error via the processor in each image block according to a fourier series model and based on pulling range and quantization level of the phase error by generating a 1D phase error and converting the 1D phase error into a 2D phase error of an image spectra for each image block and within the pulling range;

refocusing each image block according to estimated ground penetration phase error for that image block by the processor; and

forming an image mosaic comprising each refocused image block via the processor.

2. The method of claim 1, wherein the estimating ground penetration phase error further comprises:

selecting a base function for representing the phase error via the processor;

assigning a phase error magnitude via the processor;

generating the 1D phase error from the assigned phase error magnitude and the base function via the processor;

generating a 2D image spectra via a 2D fast fourier transform of each image block via the processor;

mixing the 2D phase error over the 2D image spectra via the processor;

performing an inverse 2D fast fourier transform over the phase error mixed spectra to determine an image domain via the processor;

determining phase error among multiple phase error magnitudes and multiple image blocks based on maximum image contrast via the processor;

determining a total phase error based on phase error components via the processor; and

removing the total phase error from the image spectra via the processor.

3. A system for synthetic aperture radar autofocus for ground penetration radar, the system comprising:

an antenna for transmitting a signal and for receiving a reflected signal comprising an image; and

a processor programmed to;

divide the image into a plurality of image blocks, each image block to be refocused separately

read each image block from the reflected signal;

locate prominent targets in each image block;

estimate ground penetration phase error in each image block according to phase error inputs comprising pulling range and quantization level by generating a 1D phase error and converting the 1D phase error into a 2D phase error of an image spectra for each image block and within the pulling range;

refocus each image block according to estimated ground penetration phase error for that image block; and

form an image mosaic comprising each refocused image block.

4. The system of claim 3, wherein the processor is further programmed to estimate ground penetration phase error by:

selecting a base function for representing the phase error;

assigning a phase error magnitude;

generating the 1D phase error from the assigned phase error magnitude and the base function;

generating a 2D image spectra via a 2D fast fourier transform of each image block;

mixing the 2D phase error over the 2D image spectra;

performing an inverse 2D fast fourier transform over the phase error mixed spectra to determine an image domain;

determining phase error among multiple phase error magnitudes and multiple image blocks based on maximum image contrast;

determining a total phase error based on phase error components; and

removing the total phase error from the image spectra.