Multiple target correlator system

• US 5,185,815 A
• Filed: 11/04/1991
• Issued: 02/09/1993
• Est. Priority Date: 11/04/1991
• Status: Expired due to Fees

• Current Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Original Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Inventors: Brandstetter, Robert W.
• Primary Examiner(s): COUSO, JOSE L
• Application Number:
  US07/787,813
• Time in Patent Office: 463 Days
• Field of Search: 382/31, 382/42, 382/43, 382/54, 250/396 R, 364/822, 359/20, 359/29, 359/559, 359/560, 359/561
• US Class Current: 382/211
• CPC Class Codes: G02B 27/642 Optical derotators, i.e. systems for compensating for image rotation, e.g. using rotating prisms, mirrors
• CPC Class Codes: G06V 10/88 Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters

Abstract

A multiple target correlation system for unambiguously detecting, locating and determining the orientation of an array of multiple targets or objects. The multiple target correlator provides a means for fabricating a matched filter array or multiple matched filter with multiple targets stored on a single plate and a method for interrogating this multiple target matched filter with multiple scene images thereby providing for the identification of each object or target and determining its location and orientation in coordinates that are user selectable. The multiple target correlator utilizes a multiple matched filter having two matched filters for each particular object or target stored thereon, and each matched filter is positioned at a unique angle. Since there are two matched filters for each object or target, there will be correlation at two different angles, one for each filter, and since the angular difference is unique for that object, then the difference between the matched filter angles will serve as an identification tag for that object. In addition, the angles at which the consecutive correlations occur are noted and utilized to determine the location and orientation of each of the objects.

Claims

1. A multiple target correlator system comprising:

(a) an imaging means for providing an image of an object or scene of interest;

(b) means for modulating a coherent beam with said image to form an image modulated beam;

(c) means for optically Fourier transforming said image modulated beam into a spatial frequency distribution of said image;

(d) multiple matched filter means disposed in the back focal plane of said means for optically Fourier transforming, and comprising at least one matched filter element having at least two matched filters recorded thereon for said object of interest and wherein said at least two matched filters are recorded at a predetermined unique angular difference, said spatial frequency distribution of said image multiplically interacts with said at least two matched filters resulting in first and second product signals;

(e) means for optically inverse Fourier transforming said first and second product signals to produce a pair of optical correlation signals;

(f) a correlation plane detector means, disposed in the back focal plane of said means for optically inverse Fourier transforming, for detecting said pair of optical correlation signals and producing electric output signals representative of said pair of correlation signals; and

(g) means for processing said electric output signals comprising;

storage means having said predetermined unique angular difference of said at least two matched filters stored therein;

means for receiving said electric outputs signals from said correlation plane detector; and

means for calculating the orientation of said particular object of interest and providing said particular object of interest with an identification tag.

2. The multiple target correlator system of claim 1 further comprising resolving means for calculating the position of said particular object of interest in user defined coordinates, said resolving means having means for receiving the position of said particular object of interest, in camera coordinates, from said correlation plane detector and the angular difference between said particular object and the coordinate axis of the particular scene of said particular object of interest from said storage means.

3. The multiple target correlator system of claim 2, wherein said multiple matched filter means comprises a plurality of matched filter pairs having a first and second matched filter, each filter pair recorded at a predetermined unique angular difference, each of said matched filter pairs being recorded for and corresponding to one of a plurality of objects of interest.

4. The multiple target correlator system of claim 2, wherein said imaging means comprises:

video camera means for capturing said image of said particular object of interest; and

control means connected to said video camera means, said control means being operable to drive said video camera means at a predetermined rate through a 360 degree rotation.

5. The multiple target correlator system of claim 4, wherein said means for modulating comprises a spatial light modulator, said spatial light modulator receiving said image of said particular object of interest from said video camera means.

6. The multiple target correlator system of claim 1, wherein said means for optically Fourier transforming comprises a multiple holographic lens.

7. The multiple target correlator system of claim 3, wherein each of said first and second matched filters are recorded at a predetermined unique angular difference therebetween to provide said identification tag for each of said objects of interest.

8. The multiple target correlator system of claim 1, wherein said means for optically inverse Fourier transforming includes a multiple holographic lens.

9. The multiple target correlator system of claim 3, wherein said system further comprises:

a correlation plane processor, receiving the electric output signals from said correlation plane detector, for converting said correlation signals into two dimensional linear coordinates in the camera plane; and

encoder means for converting said two dimensional linear coordinates into a form suitable for computer processing.

10. The multiple target correlator system of claim 7, wherein said means for processing comprises a processor and associated memory, said memory having said predetermined unique angular difference of each of said first and second matched filters and the angular difference between said first and second matched filters stored therein, said processor comprising said means for comparison and said resolving means.

11. The multiple target correlator system of claim 10, wherein said means for comparison includes a first software routine which calculates the orientation of said object as the difference between the angular position of said first matched filter and the position of said video camera means.

12. The multiple target correlator system of claim 11, wherein said resolving means comprises a second software routine which calculates the position of said particular object of interest in user defined coordinates based upon a trigonometric transformation from scene coordinates.

13. A method for unambiguously identifying an object and determining its location and orientation, said method comprising the steps of:

(a) scanning a scene for a particular object of interest;

(b) providing an image of said particular object of interest;

(c) modulating a coherent beam with said image to form an image modulated beam;

(d) optically Fourier transforming said image modulated beam into a spatial frequency distribution of said image;

(e) interrogating a multiple matched filter, having at least one matched filter element with at least two matched filters recorded thereon, such that said spatial frequency distribution of said image multiplically interacts with said at least two matched filters resulting in first and second product signals when there is a match between said at least two matched filters and said spatial frequency distribution;

(f) optically inverse Fourier transforming said first and second product signals to produce a pair of optical correlation signals;

(g) calculating the orientation of said particular object of interest based upon the detection of said pair of correlation signals;

(h) calculating the position of said particular object of interest based upon the detection of said pair of correlation signals; and

(i) calculating and assigning an identification tag to said particular object of interest based upon the detection of said pair of correlation signals.

14. The method according to claim 13, wherein said step of scanning comprises rotating an imaging means at a predetermined rate through a 360 degree rotation about the image plane axis.

15. The method according to claim 14, wherein said step of modulating comprises impressing the amplitude and phase information stored in said image of said particular object of interest onto said coherent beam.

16. The method according to claim 15, wherein said step of optically Fourier transforming comprises passing said image modulated beam through a multiple holographic lens.

17. The method according to claim 16, wherein said step of interrogating comprises directing said spatial frequency distribution of said image at said multiple matched filter.

18. The method according to claim 17, wherein said step of optically inverse Fourier transforming comprises passing said first and second product signals through an inverse Fourier transform lens.

19. The method according to claim 18, wherein said step of calculating the orientation of said particular object of interest comprises the steps of:

(a) determining the angular position of a first matched filter upon detection of said pair of correlation signals;

(b) determining the angular position of the imaging means upon detection of said pair of correlation signals; and

(c) subtracting the angular position of the imaging means from the angular position of said first matched filter.

20. The method according to claim 18, wherein said step of calculating and assigning an identification tag to said particular object of interest comprises the steps of:

(a) determining the angular position of a first matched filter upon detection of said pair of correlation signals;

(b) determining the angular position of a second matched filter upon detection of said pair of correlation signals; and

(c) subtracting the angular position of the second matched filter from the angular position of the first matched filter.

21. The method according to claim 18, wherein said step of calculating the position of said particular object of interest comprises resolving the linear coordinates of said particular object of interest from image plane coordinates to scene coordinates.

22. A multiple target correlator system comprising:

(a) an imaging means for providing an image of an object or some of interest;

(b) means for modulating a coherent beam with said image to form an image modulated beam;

(c) means for optically Fourier transforming said image modulated beam into a spatial frequency distribution of said image;

(d) multiple matched filter means disposed in the back focal plane of said means for optically Fourier transforming, and comprising a plurality of matched filter elements having a plurality of matched filters recorded thereon for said object of interest and wherein said plurality of matched filters are recorded at a predetermined unique angular difference, said spatial frequency distribution of said image multiplically interacts with said plurality of matched filters resulting in first and second product signals;

(e) an optical shutter array for addressing a particular matched filter element;

(f) means for optically inverse Fourier transforming said first and second product signals to produce a pair of optical correlation signals;

(g) a correlation plane detector means, disposed in the back focal plane of said means for optically inverse Fourier transforming, for detecting said pair of optical correlation signals and producing electric output signals representative of said pair of correlation signals; and

(h) means for processing said electric output signals comprising;

storage means having said predetermined unique angular difference of said plurality of matched filters stored therein;

means for receiving said electric output signals from said correlation plane detector;

means for calculating the orientation of said particular object of interest and providing said particular object of interest with an identification tag; and

resolving means for calculating the position of said particular object of interest in user defined coordinates, said resolving means having means for receiving the position of said particular object of interest, in camera coordinates, from said correlation plane detector and the angular difference between said particular object and the coordinate axis of the particular scene of said particular object of interest from said storage means.

23. The multiple target correlator system of claim 22, wherein said imaging means comprises:

video camera means for capturing said image of said particular object of interest; and

control means connected to said video camera means, said control means being operable to drive said video camera means at a predetermined rate through a 360 degree rotation.

24. The multiple target correlator system of claim 23, wherein said means for modulating comprises a spatial light modulator, said spatial light modulator receiving said image of said particular object of interest from said video camera means.

25. The multiple target correlator system of claim 22, wherein said means for optically Fourier transforming comprises a multiple holographic lens.

26. The multiple target correlator system of claim 23, wherein said multiple matched filter means comprises a plurality of matched filter pairs having a first and second matched filter, each recorded at a predetermined unique angular difference, each of said matched filter pairs being recorded for and corresponding to one of a plurality of objects of interest, the angular difference between said first and second matched filters provides said identification tag for said object.

27. The multiple target correlator system of claim 22, wherein said optical shutter array comprises an optical switching material which is programmed to only transmit light corresponding to specific matched filter elements thereby achieving selective interrogation of one or more matched filter combinations.

28. The multiple target correlator system of claim 22, wherein said means for optically inverse Fourier transforming is a multiple holographic lens.

29. The multiple target correlator system of claim 23, wherein said system further comprises:

a correlation plane processor receiving the electric output signals from said correlation plane detector for converting said correlation signals into two dimensional linear coordinates in the camera plane; and

encoder means for converting said two dimensional linear coordinates into a form suitable for computer processing.

30. The multiple target correlator system of claim 27, wherein said means for processing comprises a processor and associated memory, said memory having said predetermined unique angular difference of each of said first and second matched filters and the angular difference between said first and second matched filters stored therein, said processor comprising said means for comparison and said resolving means.

31. The multiple target correlator system of claim 30, wherein said means for comparison includes a first software routine which calculates the orientation of said object as the difference between the angular position of said first matched filter and the position of said video camera means.

32. The multiple target correlator system of claim 31, wherein said resolving means comprises a second software routine which calculates the position of said particular object of interest in user defined coordinates based upon a trigonometric transformation from scene coordinates.