Accurate target detection system

• US 20020084414A1
• Filed: 02/26/2001
• Published: 07/04/2002
• Est. Priority Date: 11/12/1998
• Status: Active Grant

• Current Assignee: Hien T. Dang, Sheldon S. Wald, Thomas K. Lo, Timothy E. Caber, Todd L. Baker
• Original Assignee: Hien T. Dang, Sheldon S. Wald, Thomas K. Lo, Timothy E. Caber, Todd L. Baker
• Inventors: Baker, Todd L., Wald, Sheldon S., Dang, Hien T., Lo, Thomas K., Caber, Timothy E.
• Granted Patent: US 6,526,394 B2
• Time in Patent Office: Days
• US Class Current: 250/336.1
• CPC Class Codes: G01S 13/723 by using numerical data
• CPC Class Codes: G01S 3/7864 T.V. type tracking systems
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

An accurate target detection system. The system includes a sensor (22) that receives electromagnetic signals and provides electrical signals in response thereto. A non-uniformity correction circuit (28, 38, 52) corrects non-uniformities in the sensor (22) based on the electrical signals and provides calibrated electrical signals in response thereto. A third circuit (30, 32, 34, 38, 42, 44, 52) determines if a target signal is present within the calibrated electrical signals and provides a target detection signal in response thereto. A fourth circuit (38, 40, 48) selectively activates or deactivates the non-uniformity correction circuit (28, 38, 52) based on the target detection signal. In a specific embodiment, the sensor (22) is an array of electromagnetic energy detectors (22), each detector providing an electrical detector output signal The non-uniformity correction circuit (28, 38, and 52) includes circuit for compensating for gain, background, and noise non-uniformities (28, 38, and 52) in the electromagnetic energy detectors. The non-uniformity correction circuit (28, 38, and 52) includes a detector gain term memory (28) for storing detector gain compensation values. The detector gain compensation values are normalized by noise estimates unique to each of the detectors. The third circuit (30, 32, 34, 38, 42, 44, and 52) includes a signal enhancement circuit for reducing noise (34, 42) in the calibrated electrical signals. The third circuit (30, 32, 34, 38, 42, 44, and 52) includes a noise estimation circuit (32, 38) that estimates noise in each of the detector output signals and provides noise estimates in response thereto. The noise estimation circuit (32, 38) further includes a noise estimator circuit (38) and a recursive background estimator (32). The third circuit (30, 32, 34, 38, 42, 44, 52) further includes a subtractor (30) for subtracting background from the calibrated electrical signals and providing background subtracted signals in response thereto. The signal enhancement circuit (34, 42) includes a frame integrator circuit for adding frames of image data (34), each frame containing data corresponding to the background subtracted signals and providing summed frames in response thereto. The third circuit (30, 32, 34, 38, 42, 44, 52) includes a first threshold circuit (44) for comparing the filtered signal to a first threshold and a second threshold and providing a threshold exceedance signal if the filtered signal is between the first threshold and the second threshold.

Claims

1. An accurate target detection system comprising:

first means for receiving electromagnetic signals and providing electrical signals in response thereto;

second means for correcting non-uniformities in said first means based on said electrical signals and providing calibrated electrical signals in response thereto;

third means for determining if a target signal is present within said calibrated electrical signals and providing a target detection signal in response thereto; and

fourth means for selectively activating or deactivating said second means based on said target detection signal.

2. The invention of claim 1 wherein said first means is an array of electromagnetic energy detectors, each detector providing an electrical detector output signal.

3. The invention of claim 2 wherein said second means includes means for compensating for gain, background, and/or noise non-uniformities in said electromagnetic energy detectors.

4. The invention of claim 3 wherein said second means includes a detector gain term memory for storing detector gain compensation values, said detector gain compensation values normalized by noise estimates.

5. The invention of claim 4 wherein said noise estimates are unique to each of said detectors.

6. The invention of claim 2 wherein said third means includes means for increasing the signal-to-noise ratio of said calibrated electrical signals.

7. The invention of claim 6 wherein said third means includes means for estimating noise in each of said detector output signals and providing noise estimates in response thereto.

8. The invention of claim 7 wherein said means for estimating noise further includes means for recursively estimating background in said electrical signals.

9. The invention of claim 8 wherein said means for estimating noise includes a noise estimator circuit and a recursive background estimator circuit.

10. The invention of claim 7 wherein said third means further includes a subtractor for subtracting background from said calibrated electrical signals and providing background subtracted signals in response thereto.

11. The invention of claim 10 wherein said means for increasing the signal-to-noise ratio of said electrical signals includes means for adding frames of image data, each frame containing data corresponding to said background subtracted signals and providing summed frames in response thereto.

12. The invention of claim 11 wherein said means for increasing the signal-to-noise ratio further includes a filter bank for increasing the signal-to-noise ratio of said summed frames and providing a filtered signal in response thereto.

13. The invention of claim 12 wherein said filter bank includes finite-impulse response filters.

14. The invention of claim 12 wherein said third means includes a first threshold circuit for comparing said filtered signal to a first threshold and a second threshold and providing a threshold exceedance signal if said filtered signal is between said first threshold and said second threshold.

15. The invention of claim 14 wherein said third means further includes a digital signal processor running a fuzzy controller that facilitates the determination of said first threshold by providing a threshold multiplier value.

16. The invention of claim 15 wherein said first threshold is a function of said threshold multiplier and noise variables for said background subtracted signals.

17. The invention of claim 16 wherein said noise variables include a mean noise offset, noise variance estimates from said background subtracted signals, and a noise statistic for accounting for moments greater than two in noise statistics of said background subtracted signals.

18. The invention of claim 10 wherein said fourth means includes a second threshold circuit for comparing said background subtracted signals to a target detection threshold and providing said target detection signal in response thereto when said background subtracted signals exceed said target detection threshold.

19. The invention of claim 18 wherein said target detection signal acts as an inhibit signal and is input to said means for estimating noise to disable said means for estimating noise when said target signal is possibly present with in said background subtracted signals.

20. The invention of claim 18 wherein said first threshold is a function of said noise variance estimates, and a second threshold multiplier.

21. A target detection system comprising:

first means for receiving electromagnetic signals within a field of view of said first means and for providing electrical signals in response thereto;

second means for compensating said first means for varying performance characteristics or signal environments;

third means for analyzing said electrical signals to determine if a target is present within said field of view, and

fourth means in communication with said third means for selectively deactivating said second means when a target is possibly present within said field of view.

22. An accurate target detection system comprising:

a sensor for receiving electromagnetic signals within a field of view of said sensor and providing electronic signals in response thereto;

a non-uniformity correction circuit for compensating said sensor for spatial non-uniformities;

a background estimation circuit for estimating background characteristics of said electromagnetic signals;

a subtraction circuit for subtracting said background characteristics from said electronic signals;

a threshold circuit for analyzing said electronic signals to determine if a target may be present in said field of view of said sensor; and

an update inhibit circuit for disabling said background estimation circuit and said non-uniformity correction circuit when a possible target is present in said field of view of said sensor.

24. The invention of claim 23 wherein said sum of said centroids and areas is weighted by said third means via said first set of values.

23. A fuzzy controller for facilitating the calculation of a false alarm rate detection threshold in a constant false alarm rate target detection system comprising:

first means for mapping an input into a first set of values defined by an input feature, said input a function of a number of alarms received during a predetermined time interval by said target detection system in response to a pre-existing false alarm rate detection threshold, and a number of desired alarms;

second means for establishing a set of fin regions based on said first set of values in accordance with an output feature; and

third means for calculating a desired change in said pre-existing false alarm rate detection threshold based on a weighted sum centroids and areas of said regions and providing said false alarm rate detection threshold in response thereto.

25. An accurate target detection method comprising the steps of:

receiving electromagnetic signals and providing electrical signals in response thereto;

correcting non-uniformities in said electrical signals and providing calibrated electrical signals in response thereto;

determining if a target signal is present within said calibrated electrical signals and providing a target detection signal in response thereto; and

selectively performing said step of correcting based on said target detection signal.