Visual Occultation to Measure Refractivity Profile

• US 20110025868A1
• Filed: 07/31/2009
• Published: 02/03/2011
• Est. Priority Date: 07/31/2009
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Tillotson, Brian J.
• Granted Patent: US 8,345,115 B2
• Time in Patent Office: Days
• US Class Current: 348/222.1
• CPC Class Codes: G01N 21/4133 Refractometers, e.g. differential
• CPC Class Codes: G01W 1/02 Instruments for indicating weather conditions by measuring two or more variables, e.g. humidity, pressure, temperature, cloud cover or wind speed G01W1/10 takes precedence

Abstract

Presented is a system and method for measuring the refractivity profile of a parcel of atmosphere comprising an image capturing device for capturing an image of a visual feature, such as a topographic feature like the horizon, combined with a lens having focal length adapted to focus an image onto image capturing device such that the combination of the lens and the image capturing device are adapted to resolve at least 100 microradians of angle, and an image processor adapted to compare a detected position of the visual feature in the image to the expected position of the visual feature. The system uses the difference between the detected position and the expected position to detect the change in arrival angle caused by atmospheric refraction of light from the visual feature as it passes through the atmosphere.

Claims

1. A refractivity profiling system, comprising:

an image capturing device for capturing an image of a visual feature;

a lens having a focal length adapted to focus an image onto said image capturing device such that a combination of said lens and said image capturing device is adapted to resolve at least 100 microradians of angle; and

an image processor adapted to compare a detected position of said visual feature of said image to an expected position of said visual feature to detect a change in arrival angle caused by atmospheric refraction of air between the refractivity profiling system and said visual feature.

2. The refractivity profiling system of claim 1, wherein said image processor is adapted to process said change in arrival angle to determine a refractivity profile of a parcel of atmosphere.

3. The refractivity profiling system of claim 1, wherein said image capturing device is a CCD camera.

4. The refractivity profiling system of claim 1, wherein said visual feature is a topographical feature.

5. The refractivity profiling system of claim 1, further comprising:

an inertial navigation device providing an orientation data of the refractivity profiling system relative to said visual feature; and

a global positioning system data providing a position of the refractivity profiling system relative to said visual feature, and

wherein said image processor is adapted to process said global positioning system data and said orientation data to query a geographic information system source for a location of said visual feature, and wherein said image processor is adapted to compute an expected position of said visual feature.

6. The refractivity profiling system of claim 5, wherein said image processor is adapted to compare said image with an image data from said geographic information system source to detect one of a compression of said visual feature and an inversion of said visual feature.

7. The refractivity profiling system of claim 5, wherein said image processor is adapted to process said one of a compression of said visual feature and an inversion of said visual feature to determine a change in departure angle of a light from said visual feature.

8. The refractivity profiling system of claim 7, wherein said image processor is adapted to process said arrival angle and said departure angle to determine a refractivity profile of a parcel of atmosphere.

9. A method of detecting a refractivity profile of a parcel of atmosphere, comprising:

capturing an image from a platform having an orientation and a position;

selecting a feature present in said image;

computing an expected angular position of said feature in said image; and

comparing an observed angular position of said feature in said image with said expected angular position to derive a change in arrival angle, said change in arrival angle being correlated with the refractivity profile.

10. The method of claim 9, wherein said capturing is performed by an image capturing means adapted to capture angular resolutions of approximately 10 microradians to approximately 100 microradians of said image.

11. The method of claim 9, wherein said feature is a horizon.

12. The method of claim 9, wherein said platform is an aircraft.

13. The method of claim 9, further comprising:

determining a refractivity profile of the parcel of atmosphere from said change in arrival angle.

14. The method of claim 13, further comprising:

predicting a temperature and humidity of the parcel of atmosphere from said refractivity profile.

15. The method of claim 9, further comprising:

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

comparing said image to said image data to determine a change in departure angle of a light from said feature, wherein said comparing measures a change in said feature selected from the group consisting of a compression of said feature, and an inversion of said feature; and

determining a refractivity profile based at least in part on said change in departure angle.

16. The method of claim 9, further comprising:

capturing a first image of a first horizon in a first direction;

capturing a second image of a second horizon in a second direction;

correlating said first horizon in said first image with said second horizon in said second image to determine said orientation of said platform.

17. An aircraft with a refractivity profiling system, comprising:

a CCD camera for capturing an image of a topographical feature, said CCD camera adapted to resolve a change in an arrival angle of said topographical feature caused by an atmospheric refraction of a parcel of atmosphere between said CCD camera and said topographical feature;

an aircraft adapted to mount said CCD camera; and

a processor in said aircraft adapted to compare a detected angular position of said visual feature of said image to an expected angular position of said topographical feature to determine said change in arrival angle, and wherein said processor is adapted to derive a refractivity profile of said parcel of atmosphere from said change in arrival angle.

18. The aircraft of claim 17, further comprising:

an inertial navigation device providing an orientation data of the aircraft relative to said topographical feature; and

a global positioning system data providing a position of the aircraft relative to said topographical feature, 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 a data relating to said topographic feature, and

wherein said processor is adapted to compute an expected angular position of said topographical feature from said data, and

wherein said processor is adapted to compare said expected angular position with an angular position of said topographical feature in said image to determine a change in departure angle of a light from said topographical feature by detecting one of a compression of said topographical feature and an inversion of said topographical feature, and

wherein said processor is adapted to derive a refractivity profile of said parcel of atmosphere from said change in departure angle.

19. The aircraft of claim 17, wherein said processor is adapted to predict a temperature and a humidity of the parcel of atmosphere from said refractivity profile, and further comprising a display for presenting said temperature and said humidity.

20. The aircraft of claim 17, further comprising:

a communications link adapted to transmit said position and said refractivity profile; and

a receiving station adapted to receive a plurality of said refractivity profiles and said positions from a refractivity profiling system, said receiving station adapted to aggregate said plurality of said refractivity profiles and said positions into a refractivity profile correlated with altitude when said refractivity profiles overlap a common area and said positions include different altitudes.