Visual detection of clear air turbulence

• US 8,339,583 B2
• Filed: 07/17/2009
• Issued: 12/25/2012
• Est. Priority Date: 07/17/2009
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Tillotson, Brian J.
• Primary Examiner(s): Backer, Firmin
• Assistant Examiner(s): Chambers, Michael A
• Application Number:
  US12/505,182
• Publication Number:
  US 20110013016A1
• Time in Patent Office: 1,257 Days
• Field of Search: 356/28, 455/431, 340/628, 701/472
• US Class Current: 356/28
• CPC Class Codes: G01N 2021/4106 Atmospheric distortion; Turbulence
• CPC Class Codes: G01N 21/41 Refractivity; Phase-affecting properties, e.g. optical path length G01N21/21 takes precedence
• CPC Class Codes: G01W 1/00 Meteorology
• CPC Class Codes: G01W 2001/003 Clear air turbulence detection or forecasting, e.g. for aircrafts

Abstract

Presented is a system and method for detecting clear air turbulence comprising an image capturing element, a lens having focal length adapted to focus a scene onto the image capturing element such that the combination of the lens and array of pixels are capable of optically resolving any visual distortions of features in the scene that are caused by turbulent air, and a processor. The processor compares the image with a subsequent image, or a stored image of the scene, to detect a change in refraction of light received from the feature in the scene that is due to turbulence and produces an indication of the area of turbulence in the scene.

Claims

1. A clear air turbulence detection system, comprising:

an image capturing element configured to capture an ambient light image of a scene;

a lens having a focal length adapted to focus said scene onto said image capturing element such that a combination of said lens and said image capturing element is adapted to optically resolve a visual distortion of a feature in said scene due to turbulence; and

a processor adapted to process said image of said scene from said image capturing element, said processor being adapted to compare a plurality of said images, captured at pre-set time intervals, to detect a non-uniform change in refraction of light received from said feature from one of said plurality of said images to a next successive one of said plurality of images due to turbulence and produce an indication of an area of turbulence.

2. The clear air turbulence detection system of claim 1, wherein said image capturing element is a CCD camera.

3. The clear air turbulence detection system of claim 1, wherein said lens is a telephoto lens.

4. The clear air turbulence detection system of claim 1, wherein said combination of said lens and said image capturing element is adapted to have a minimum resolving capability of between approximately 10 microradians of angle and approximately 100 microradians of angle.

5. The clear air turbulence detection system of claim 1, wherein the clear air turbulence system is mounted on a moving platform and wherein said processor is further adapted to transform scene in a first one of said images relative to said scene in a second, successive one of said images such that a feature in said first one of said images approximates a position, a size and an orientation of said feature in said second one of said images.

6. The clear air turbulence detection system of claim 5, wherein said processor is adapted to transform said scene in said first one of said images using a transformation selected from the group consisting of translating said scene, scaling said scene, rotating said scene, and projecting said scene.

7. The clear air turbulence detection system of claim 5, further comprising:

an inertial navigation device providing an orientation data of said feature; and

global positioning system data providing a position of said moving platform, and wherein said processor is adapted to process said global positioning system data and said orientation data to query a geographic information system source for image data of said feature, and

wherein said processor is adapted to compare an image of said feature captured by said image capturing element with said image data of said feature from said geographic information system source to detect a change in spatial information content of said feature due to an area of turbulence.

8. The clear air turbulence detection system of claim 1, wherein said processor detects said change in refraction of said feature due to an area of turbulence by performing a power spectral density operation selected from the group consisting of measuring a decrease in a high spatial frequency content of a measured power spectral density of a feature of an image compared with a calculated power spectral density of said feature of said image, and an increase in a high frequency content of a measured temporal power spectral density of a feature over a plurality of images compared with a calculated power spectral density of said feature over said plurality of images.

9. The clear air turbulence detection system of claim 1, wherein said processor detects turbulence by detecting angular blurring in an image.

10. The clear air turbulence detection system of claim 1, wherein said processor detects turbulence by detecting temporal flickering between images.

11. The clear air turbulence detection system of claim 1, wherein said processor detects a range to said turbulence by tracking a size of an area of scintillation through a plurality of images to determine a rate of change in an angular extent of said area of scintillation.

12. The clear air turbulence detection system of claim 1, wherein said turbulence indication is selected from the group consisting of an audible alarm, a graphical display of said turbulence, a graphical overlay superimposed on a real-time image, an input to an autopilot navigation system, and a broadcasted electronic message.

13. A method of detecting clear air turbulence, comprising:

capturing a first image of a scene illuminated by ambient light;

capturing a second image, at a pre-set time interval subsequent to capturing said first image, consisting essentially of said scene illuminated by ambient light;

selecting a feature present in said first image and said second image;

registering said first image to said second image such that said feature in said first image has approximately a same position, scale, and orientation as said feature in said second image;

comparing said feature in said first image with said feature in said second image to determine a non-uniform change to a portion of said feature between said first image and said second image; and

displaying a turbulence indication if said non-uniform change to said feature is present above a pre-set threshold.

14. The method of detecting clear air turbulence of claim 13, wherein said first image and second image are adapted to resolve a minimum angular resolution of approximately 10 microradians to approximately 100 microradians.

15. The method of detecting clear air turbulence of claim 13, further comprising:

removing a change to a portion of said feature caused by moving objects.

16. The method of detecting clear air turbulence of claim 13, further comprising:

detecting an angular blurring in an image; and

displaying a turbulence indication base upon said angular blurring.

17. The method of detecting clear air turbulence of claim 13, further comprising:

detecting a temporal flickering in a set of images; and

displaying a turbulence indication base upon said temporal flickering.

18. The method of detecting clear air turbulence of claim 13, wherein said change to a portion of said feature is an increase in a high temporal frequency content of a power spectrum distribution of said feature.

19. The method of detecting clear air turbulence of claim 13, further comprising:

computing a power spectral density of said feature of said second image;

computing a power spectral density of said feature of said first image; and

comparing said power spectral density of a said first image and said second image to determine said turbulence indication.

20. The method of detecting clear air turbulence of claim 13, further comprising:

receiving an orientation data of said orientation of said scene of said first image relative to said feature;

receiving a position data of a distance to said feature of said first image; and

transforming said scene of said second image to have approximately a same position, scale, and orientation as said feature in said first image.

21. The method of detecting clear air turbulence of claim 20, further comprising:

querying a geographic information service for a data correlating to said feature; and

computing said feature of said second image from the data of said geographic information service.

22. The method of detecting clear air turbulence of claim 13, wherein said displaying a turbulence indication is selected from the group consisting of playing an audible alarm, displaying a graphical display of said turbulence, superimposing a graphical overlay on a real-time image, sending a message to an autopilot navigation system, and broadcasting an electronic message.

23. An aircraft with a turbulence detection system, comprising:

a turbulence detection system having a camera system and an image processing system;

said camera system being configured to capture an ambient light image of a scene;

said image processing system including a processor adapted to process said image of said ambient light image of said scene by comparing a plurality of said ambient light images of said scene, captured at pre-set time intervals, to detect a non-uniform change in refraction of ambient light received from said scene from one of said plurality of said images to a next successive one of said plurality of said images due to turbulence, and produce an indication of an area of turbulence;

an aircraft adapted to mount said camera system; and

a turbulence alerting system in a cockpit of said aircraft, said turbulence alerting system being in electronic communication with said image processing system.

24. The aircraft of claim 23, wherein said camera system further comprises:

a CCD camera having a pixel size and focal length adapted to resolve visual distortions in a scene imaged by said CCD camera that are caused by turbulent air.

25. The aircraft of claim 23, wherein said image processing system is adapted to select a selected image from said plurality of images, to select a reference image with which to compare said selected image, to perform a geometric image transformation selected from the group consisting of translating a scene, scaling a scene, rotating a scene, and projecting a scene, said geometric image transformation registering scenes from two different perspectives with one another, and to compare said selected image to said reference image to produce said indication of turbulence.

26. The aircraft of claim 25, wherein said reference image is selected from the group consisting of a second selected image from said plurality of images, a previously stored image of the scene, an image of the scene from a geographic information system, and an image of a feature in the scene from a geographic information system.

27. The aircraft of claim 23, wherein said image processing system detects a change selected from the group consisting of an angular blurring of a feature in an image, a temporal flickering of a feature in a set of images, a change in size of an area of scintillation of a feature in an image, a change in high temporal frequency content of a feature in an image, and a change in power spectral density of a feature in an image.

28. The aircraft of claim 23, wherein said turbulence alerting system receives said indication of turbulence from said image processing system, and said turbulence alerting system is selected from the group consisting of an audible alarm, a graphical display of said turbulence, a graphical overlay superimposed on a real-time image, an input to an autopilot navigation system, and a broadcasted electronic message.