FLIR-to-missile boresight correlation and non-uniformity compensation of the missile seeker

• US 7,463,753 B2
• Filed: 09/15/2004
• Issued: 12/09/2008
• Est. Priority Date: 09/15/2004
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Williams, Darin S., Kitchen, Edward N.
• Primary Examiner(s): Mehta; Bhavesh M
• Assistant Examiner(s): Bhatnagar; Anand
• Application Number:
  US10/941,203
• Publication Number:
  US 20080112594A1
• Time in Patent Office: 1,546 Days
• Field of Search: 382/100, 382/103, 382/106, 382/107, 382/181, 382/190, 382/195, 382/199, 382/201, 382/203, 342/52, 342/53, 342/141, 250/316.1, 250/330, 250/336.1, 250/338.1, 250/341.8, 250/342, 250/495.1, 702/127, 702/135, 702/134, 348/169
• US Class Current: 382/103
• CPC Class Codes: F41G 7/007 Preparatory measures taken before the launching of the guided missiles
• CPC Class Codes: F41G 7/2226 comparing the observed data with stored target data, e.g. target configuration data
• CPC Class Codes: F41G 7/2253 Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
• CPC Class Codes: F41G 7/2293 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 3/7803 Means for monitoring or calibrating
• CPC Class Codes: H04N 25/674 based on the scene itself, e.g. defocusing
• 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

The present invention provides for simple and streamlined boresight correlation of FLIR-to-missile video. Boresight correlation is performed with un-NUCed missile video, which allows boresight correlation and NUC to be performed simultaneously thereby reducing the time required to acquire a target and fire the missile. The current approach uses the motion of the missile seeker for NUCing to produce spatial gradient filtering in the missile image by differencing images as the seeker moves. This compensates DC non-uniformities in the image. A FLIR image is processed with a matching displace and subtract spatial filter constructed based on the tracked scene motion. The FLIR image is resampled to match the missile image resolution, and the two images are preprocessed and correlated using conventional methods. Improved NUC is provided by cross-referencing multiple measurements of each area of the scene as viewed by different pixels in the imager. This approach is based on the simple yet novel premise that every pixel in the array that looks at the same thing should see the same thing. As a result, the NUC terms adapt to non-uniformities in the imager and not the scene.

Claims

1. A method of providing target handover from a missile launch system having an infrared (IR) imager that provides high resolution launch system video to a missile having a missile seeker with an IR imager that provides low resolution missile video, comprising:

receiving missile video from the missile seeker'"'"'s IR imager;

receiving launch system video from the launch system'"'"'s IR imager;

performing a boresight correlation of the missile video to the launch system video to align the seeker'"'"'s IR imager to the launch system'"'"'s IR imager;

performing non-uniformity compensation (NUC) on the missile video to compute NUC terms for the seeker'"'"'s IR imager, said computed NUC terms not being applied to the missile video used in the performance of the boresight correlation; and

handing over the alignment and NUC terms for the seeker'"'"'s IR imager to the missile seeker.

2. The method of claim 1, wherein boresight correlation is performed by,

using temporal motion of the seeker over a plurality of frames of missile video to form a first edge map;

measuring scene motion in the missile video;

spatially processing images in the launch system video in accordance with the measured scene motion to locate at least some of the same edges to form a second edge map; and

correlating the first and second edge maps.

3. The method of claim 2, wherein the first edge map is formed by differencing images in the missile video.

4. The method of claim 3, wherein a first frame of the missile video is subtracted from a second frame to form the first difference image.

5. The method of claim 2, wherein the launch system video is spatially processed with a displace and subtract filter in accordance with the measured scene motion.

6. The method of claim 1, wherein the non-uniformity compensation is performed on the missile video by,

registering a temporal sequence of input images from the missile video having different fields of view (FOVs) to create an estimate of an input scene;

backward mapping the estimated input scene to the different FOVs to create an estimate input image for each input image;

comparing each said estimate input image to its associated input image to estimate pixel-by-pixel response NUC terms for the seeker'"'"'s IR imager; and

applying the NUC terms to the images to generate compensated images.

7. The method of claim 6, wherein the estimate of the input scene is created by a forward mapping of,

adding the registered input images together to create a registered sum image;

accumulating the number of input images that contribute to each pixel in the scene in a registered count image;

dividing the registered sum image by the registered count image to form a registered average image as the estimate.

8. The method of claim 7, further comprising keeping track of a variability of the response of the imager pixels in the forward mapping to update the registered sum image, wherein imager pixels that provide the most consistent response contribute most heavily to the registered sum and registered count images, hence the estimate of the input scene.

9. The method of claim 7, wherein the registered average image is maintained at a higher resolution than the input image.

10. The method of claim 9, wherein a nearest neighbor mapping is used to expand the number of pixels in the FOV of the input image into the registered average image, phase variation in the input images causing aliased frequency components from the mapping to cancel while artifacts that are consistent with beyond-Nyquist frequencies in the input image add constructively and are preserved.

11. The method of claim 7, wherein said backward mapping comprises convolving the FOV motion trace against the registered average image to form an ideal stacked average that is compared to a stacked average of the input images to form a composite unexplained difference image that is output as the NUC error terms to update the NUC terms, said NUC error terms being correlated again the FOV motion trace and added to the registered sum image to update the registered average image for another iteration on the NUC error terms.

12. The method of claim 6, wherein the estimated input scene is backward mapped to each input image by cutting out a frame in the estimated input scene that corresponds to that input image'"'"'s field of view.

13. The method of claim 12, further comprising keeping track of a variability of the scene pixels in the backward mapping to update the estimated NUC terms, wherein those areas of the estimate of the input scene which are temporally stable and locally flat contribute most heavily to the estimate of the NUC terms.

14. The method of claim 6, wherein the NUC terms are estimated by,

differencing respective pairs of input images and estimated input images to form a sequence of unexplained difference images;

performing an Nth order correlation on said unexplained difference images to form NUC error terms; and

combining the NUC error terms with the NUC terms to update the NUC terms.

15. The method of claim 6, wherein the steps are repeated on the compensated images to improve the estimate of the NUC terms.

16. The method of claim 6, further comprising:

computing a scene pixel variability map;

for each pixel (i,j) in the scene, determine the number N(i,j) of images to merge based on the variability map;

for each pixel in the scene, selecting the most recent N(i,j) images that contribute to said pixel, and

merging the N(i,j) values from the selected images for each pixel to form a composite image.

17. The method of claim 16, wherein a video sequence of said composite images is displayed.

18. A method of providing target handover from a missile launch system having an infrared (IR) imager that provides high resolution launch system video to a missile having a missile seeker with an IR imager that provides low resolution missile video, comprising:

receiving missile video from the missile seeker'"'"'s IR imager;

receiving launch system video from the launch system'"'"'s IR imager;

performing a boresight correlation of the missile video to the launch system video to align the seeker'"'"'s IR imager to the launch system'"'"'s IR imager;

performing non-uniformity compensation (NUC) to compute NUC terms for the seeker'"'"'s IR imager by registering a temporal sequence of input images from the missile video having different fields of view (FOVs) to create an estimate of an input scene, backward mapping the estimated input scene to the different FOVs to create an estimate input image for each input image, and comparing each said estimate input image to its associated input image to estimate pixel-by-pixel response NUC terms, said computed NUC terms not being applied to the missile video used in the performance of the boresight correlation; and

handing over the alignment and NUC terms for the seeker'"'"'s IR imager to the missile seeker.

19. A method of providing target handover from a missile launch system having an infrared (IR) imager that provides high resolution launch system video to a missile having a missile seeker with an IR imager that provides low resolution missile video, comprising:

receiving missile video from the missile seeker'"'"'s IR imager;

receiving launch system video from the launch system'"'"'s IR imager;

performing a boresight correlation using temporal motion of the seeker over a plurality of frames of missile video to form a first edge map, measuring scene motion in the missile video, spatially processing images in the launch system video in accordance with the measured scene motion to locate at least some of the same edges to form a second edge map and correlating the first and second edge maps to align the seeker'"'"'s IR imager to the launch system'"'"'s IR imager;

performing non-uniformity compensation (NUC) on the missile video to compute NUC terms for the seeker'"'"'s IR imager, said computed NUC terms not being applied to the missile video used in the performance of the boresight correlation; and

handing over the alignment and NUC terms for the seeker'"'"'s IR imager to the missile seeker.