SAR AUTOFOCUS FOR GROUND PENETRATION RADAR

• US 20140015710A1
• Filed: 01/10/2012
• Published: 01/16/2014
• 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.
• Granted Patent: US 9,041,585 B2
• Time in Patent Office: Days
• US Class Current: 342/25.F
• 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 (100). The method includes transmitting a signal via an antenna (102); receiving a reflected signal comprising a plurality of image blocks via the antenna (102); reading each image block from the reflected signal (602) via a processor (108); locating prominent targets in each image block (604) via the processor (108); estimating ground penetration phase error (606) via the processor (108) in each image block via phase error inputs (608) including pulling range and quantization level by generating a 1D phase error (706) and converting the 1D phase error into a 2D phase error of an image spectra (708); refocusing each image block according to estimated ground penetration phase error for that image block (610) via the processor (108); and forming an image mosaic comprising each refocused image block (614) via the processor (108).

Claims

1. A method of synthetic aperture radar autofocus for ground penetration radar (100), the method comprising:

transmitting a signal via an antenna (102);

receiving a reflected signal comprising a plurality of image blocks via the antenna (102);

reading each image block from the reflected signal (602) via a processor (108);

locating prominent targets in each image block (604) via the processor (108);

estimating ground penetration phase error (606) via the processor (108) in each image block via phase error inputs (608) comprising pulling range and quantization level by generating a 1D phase error (706) and converting the 1D phase error into a 2D phase error of an image spectra (708);

refocusing each image block according to estimated ground penetration phase error for that image block (610) via the processor (108); and

forming an image mosaic comprising each refocused image block (614) via the processor (108).

2. The method of claim 1, wherein the estimating ground penetration phase error (606) further comprises:

assigning an order of base functions (702) via the processor (108);

assigning a phase error magnitude (704) via the processor (108);

generating the 1D phase error from the assigned phase error magnitude and the base function (706) via the processor (108);

generating a 2D image spectra via a 2D fast fourier transform (714) of each image block (712) via the processor (108);

mixing the 2D phase error over the 2D image spectra (710) via the processor (108);

performing an inverse 2D fast fourier transform (716) over the phase error mixed spectra to determine an image domain (718) via the processor (108);

determining phase error among multiple phase error magnitudes and multiple image blocks based on maximum image contrast (722) via the processor (108);

determining a total phase error based on phase error components (726) via the processor (108); and

removing the total phase error from the image spectra via the processor (108).

3. A system for synthetic aperture radar autofocus for ground penetration radar (100), the system comprising:

an antenna (102) for transmitting a signal and for receiving a reflected signal comprising a plurality of image blocks; and

a processor (108) programmed to;

read each image block from the reflected signal (602);

locate prominent targets in each image block (604);

estimate ground penetration phase error (606) in each image block via phase error inputs (608) comprising pulling range and quantization level by generating a 1D phase error (706) and converting the 1D phase error into a 2D phase error of an image spectra (708);

refocus each image block according to estimated ground penetration phase error for that image block (610); and

form an image mosaic comprising each refocused image block (614).

4. The system of claim 3, wherein the processor (108) is further programmed to estimate ground penetration phase error (606) by:

assigning an order of base functions (702);

assigning a phase error magnitude (704);

generating the 1D phase error from the assigned phase error magnitude and the base function (706);

generating a 2D image spectra via a 2D fast fourier transform (714) of each image block (712);

mixing the 2D phase error over the 2D image spectra (710);

performing an inverse 2D fast fourier transform (716) over the phase error mixed spectra to determine an image domain (718);

determining phase error among multiple phase error magnitudes and multiple image blocks based on maximum image contrast (722);

determining a total phase error based on phase error components (726); and

removing the total phase error from the image spectra.