Optical device for correcting geostationary satellite imagery for earth curvature effects

• US 7,676,112 B2
• Filed: 04/27/2007
• Issued: 03/09/2010
• Est. Priority Date: 05/01/2006
• Status: Expired due to Fees

• Current Assignee: University Corporation For Atmospheric Research
• Original Assignee: University Corporation For Atmospheric Research
• Inventors: Johnson, David B.
• Primary Examiner(s): Johns; Andrew W
• Assistant Examiner(s): Cunningham; Gregory F
• Application Number:
  US11/741,405
• Publication Number:
  US 20070292046A1
• Time in Patent Office: 1,047 Days
• Field of Search: 353/69, 359/654, 382/275
• US Class Current: 382/275
• CPC Class Codes: G02B 13/18 with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration G02B13/002 takes precedence
• CPC Class Codes: G02B 27/0911 Anamorphotic systems
• CPC Class Codes: G06T 3/073 Transforming surfaces of revolution to planar images, e.g. cylindrical surfaces to planar images
• CPC Class Codes: G06T 5/80 Geometric correction

Abstract

An optical adapter for an imaging system correcting images of spherical or near spherical bodies such as the earth during satellite image collection. An imaging system includes an image collector that collects a two-dimensional image of the body from a distance above the body such as from a satellite in geostationary orbit. The collected image is disk shaped and includes distortion due to earth curvature, primarily in the form of a loss of resolution due to the foreshortening of earth features in a radial direction extending outward from the center of the image disk. The optical adapter receives the collected image, transforms the collected image to correct the distortion, and outputs a corrected image with essentially uniform spatial resolution across the areas for which the correction is applied. An image sensor such as charge-coupled device array senses the corrected image and creates a digital representation of the corrected image.

Claims

1. An imaging system for use in transforming images of a spherical body during image collection, comprising:

an image collector collecting an image of the body from a distance above the body, wherein the collected image is substantially disk shaped and includes distortion in portions that are radially spaced apart from a center of the disk-shaped image, wherein at least some of the radially-spaced, distorted portions extend along a line of longitude and at least some of the radially-spaced, distorted portions extend along a line of latitude that is generally perpendicular to the line of longitude; and

wherein the distortion is due to curvature of the spherical body or due to oblique viewing angles;

an optical adapter receiving the collected image and transmitting a corrected image comprising the collected image with a correction to enhance resolution in the distorted portions; and

an image sensor with a receiving surface for sensing the corrected image.

2. The system of claim 1, wherein the corrected image is transformed by the optical adapter to have substantially uniform resolution.

3. The system of claim 1, wherein the imaging system is mounted upon a satellite for use in geostationary orbit and the image collector comprises a fixed telescope in geostationary orbit directed straight downward towards the center of the spherical body.

4. The system of claim 1, wherein the correction to enhance resolution comprises radial stretching segments of the collected image in the distorted portions that are radially spaced apart from a center of the disk-shaped image to have a size substantially equivalent to image segments that are near the center of the collected image relative to the distorted portions.

5. The system of claim 4, wherein the corrected image has a diameter that is larger than the collected image by a factor of less than 1.4.

6. The system of claim 1, wherein the corrected image has a diameter that is substantially equivalent or smaller than a diameter of the collected image.

7. The system of claim 1, wherein the optical adapter is provided as an integral component of the image collector.

8. The system of claim 1, wherein the correction to enhance resolution is selected from a group of corrections consisting of equal area correction, curvature correction, equidistant correction, and stereographic correction.

9. The system of claim 8, wherein the optical adapter is configured based on a radial stretching factor that defines an amount of stretching applied to the collected image relative to the center of the collected image and wherein the radial stretching factor is defined by a curve corresponding to the correction selected from the group of corrections.

10. The system of claim 1, wherein the optical adapter provides the correction of the collected image applying pincushion distortion to the collected image.

11. An optical adapter for use in a remote sensing system for correction of distortions due to earth curvature or oblique viewing angles, comprising:

a first component for receiving an earth view comprising portions that are relatively near an edge of the earth view that are distorted relative to portions of the earth view that are relatively near a center of the earth view, wherein the distortions are due to earth curvature or oblique viewing angles;

one or more optical components for generating a corrected earth view by progressively transforming the distorted portions to correct at least a portion of distortion in the received earth view;

wherein the one or more optical components substantially continuously transform the earth view from the portions that are relatively near a center of the earth view to the distorted portions that are relatively near an edge of the earth view; and

a second component for transmitting the corrected earth view to a sensor.

12. The adapter of claim 11, wherein the one or more optical components are configured to distort the earth view to provide uniform resolution across substantially all of the earth view.

13. The adapter of claim 11, wherein the one or more optical components comprise an aspheric lens or mirror with increasing curvature near an edge portion.

14. The adapter of claim 11, wherein the earth view is divided into two or more areas and wherein each of the areas is transformed separately to correct for distortion.

15. The adapter of claim 11, wherein the received earth view is collected by the remote sensing system at an offset from nadir using conical scanning.

16. The adapter of claim 11, wherein the adapter is configured for transforming linear sections of the earth view and wherein the remote sensing system comprises a linear array that is conically scanned to gather linear sections.

17. The adapter of claim 11, wherein the remote sensing system comprises a linear array that is operated using a pushbroom scan to gather linear sections that are transformed by the adapter.

18. A method for correcting geostationary satellite imagery, comprising:

obtaining an earth image comprising portions distal to a center of the earth image with distortion due to curvature effects;

wherein at least some of the portions extend along a line of longitude and at least some of the portions extend along a line of latitude that is generally perpendicular to the line of longitude;

radially stretching at least some of the portions that extend along the line of longitude and at least some of the portions that extend along the line of latitude of the earth image having distortion to correct for the curvature effects to generate a corrected earth image; and

transmitting the corrected earth image onto an image sensor.

19. The method of claim 18, wherein the stretching is performed at a greater rate on image segments in the portions near an edge of the earth image and wherein coverage of the corrected earth image extends outward from nadir by an earth angle of less than 65 degrees.

20. The method of claim 18, wherein the stretching is performed with an aspheric lens or mirror with greater curvature near its edge and wherein the stretching is performed such that substantially uniform resolution is provided across the corrected earth image.