Two-stage detection and discrimination system for side scan sonar equipment

• US 5,493,539 A
• Filed: 03/11/1994
• Issued: 02/20/1996
• Est. Priority Date: 03/11/1994
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Gilmour, John E., Haley, Paul H.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US08/209,097
• Time in Patent Office: 711 Days
• Field of Search: 367/88, 367/131, 382/27, 382/50, 382/54, 382/23, 382/36
• US Class Current: 367/88
• CPC Class Codes: G01S 15/8902 Side-looking sonar
• CPC Class Codes: G01S 7/539 using analysis of echo signal for target characterisation; Target signature; Target cross-section

Abstract

An automatic method for finding mines in side scan sonar images using a two-stage detection/discrimination process is provided. This method improves the discrimination process by specialized processing of regions of interest found in the detection process to increase the probability of correctly identifying highlight and shadow regions associated with mine images. Features specifically selected for their ability to discriminate mines are then extracted from these areas for use in the Bayesian discriminator.

Claims

1. A system for discriminating candidate mine targets detected by a side scan sonar system, said candidate mine targets consisting of snippet images formed from a matrix of pixels, each snippet image having highlight areas and shadow areas having known greyness levels, comprising:

a. a highlight filter to expand the size of each said highlight area of each said snippet image by a predefined amount to generate highlight filtered snippet images, whereby adjacent highlight areas in each said snippet image are coalesced to form a single highlight area;

b. a highlight mask generator which generates a highlight mask from said highlight filtered snippet images by computing a highlight threshold greyness level and analyzing said highlight filtered snippet images using said highlight threshold greyness level;

c. a highlight feature extractor which extracts highlight features of said snippet images by comparing said highlight mask and said snippet images;

d. a shadow filter to expand the size of the areas in said snippet image exhibiting speckle to coalesce those areas of said snippet image exhibiting speckle to generate shadow filtered snippet images, whereby said shadow areas in said snippet image are represented by those areas of said snippet image exhibiting a lack of speckle;

e. a shadow mask generator which generates a shadow mask from said shadow filtered snippet images by selecting those shadow areas in said shadow filtered snippet image which meet area and greyness requirements;

f. a shadow feature extractor which extracts shadow features of said snippet images by comparing said shadow mask and said snippet images;

g. a joint highlight/shadow feature calculator which calculates joint highlight/shadow features from said highlight features and said shadow features; and

h. a Bayesian discriminator which analyzes said highlight features, said shadow features and said joint highlight/shadow features to determine whether said features correspond to predefined results which indicate the presence of a mine.

2. A system for discriminating candidate mine targets detected by a side scan sonar system, said candidate mine targets consisting of snippet images formed from a matrix of pixels, each snippet image having highlight areas and shadow areas having known greyness levels, comprising:

a. means for expanding the size of each said highlight area of each said snippet image by a predefined amount to generate highlight filtered snippet images, whereby adjacent highlight areas in each said snippet image are coalesced to form a single highlight area;

b. means for generating a highlight mask from said highlight filtered snippet images by computing a highlight threshold greyness level and analyzing said highlight filtered snippet images using said highlight threshold greyness level;

c. means for extracting highlight features of said snippet images by comparing said highlight mask and said snippet images;

d. means for expanding the size of the areas in said snippet image exhibiting speckle to coalesce those areas of said snippet image exhibiting speckle to generate shadow filtered snippet images, whereby said shadow areas in said snippet image are represented by those areas of said snippet image exhibiting a lack of speckle;

e. means for generating a shadow mask from said shadow filtered snippet images by selecting those shadow areas in said shadow filtered snippet image which meet area and greyness requirements;

f. means for extracting shadow features of said snippet images by comparing said shadow mask and said snippet images;

g. means for calculating joint highlight/shadow features from said highlight features and said shadow features; and

h. means for analyzing said highlight features, said shadow features and said joint highlight/shadow features to determine whether said features correspond to predefined results which indicate the presence of a mine.

3. The system of claim 2 wherein said means for analyzing is a Bayesian discriminator.

4. The system of claim 2 wherein said means for expanding the size of each said highlight area of each said shipper image by a predefined amount is a highlight filter.

5. The system of claim 2 wherein said means for expanding the size of the areas in said snippet image exhibiting speckle to coalesce those areas of said snippet image exhibiting speckle is a shadow filter.

6. A method for discriminating candidate mine targets detected by a side scan sonar system, said candidate mine targets consisting of snippet images formed from a matrix of pixels, each snippet image having highlight areas and shadow areas having known greyness levels, comprising the steps of:

a. filtering said snippet images to expand the size of each said highlight area of each said snippet image by a predefined amount to generate highlight filtered snippet images, whereby adjacent highlight areas in each said snippet image are coalesced to form a single highlight area;

b. generating a highlight mask from said highlight filtered snippet images by computing a highlight threshold greyness level and analyzing said highlight filtered snippet images using said highlight threshold greyness level;

c. extracting highlight features of said snippet images by comparing said highlight mask and said snippet images;

d. filtering said snippet images to expand the size of the areas in said shipper image exhibiting speckle to coalesce those areas of said shipper image exhibiting speckle to generate shadow filtered snippet images, whereby said shadow areas in said snippet image are represented by those areas of said snippet image exhibiting a lack of speckle;

e. generating a shadow mask from said shadow filtered snippet images by selecting those shadow areas in said shadow filtered snippet image which meet area and greyness requirements;

f. extracting shadow features of said snippet images by comparing said shadow mask and said snippet images;

g. calculating joint highlight/shadow features from said highlight features and said shadow features; and

h. analyzing said highlight features, said shadow features and said joint highlight/shadow features to determine whether said features correspond to predefined results which indicate the presence of a mine.