Method and apparatus for wide field distortion-compensated imaging

• US 5,448,053 A
• Filed: 12/20/1993
• Issued: 09/05/1995
• Est. Priority Date: 03/01/1993
• Status: Expired due to Term

• Current Assignee: Pacific Northwest Trust Co.
• Original Assignee: Pacific Northwest Trust Co.
• Inventors: Rhoads, Geoffrey B.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): LE, QUE TAN
• Application Number:
  US08/171,661
• Time in Patent Office: 624 Days
• Field of Search: 250/201.9, 250/216, 250/205, 356/121, 382/29, 382/43
• US Class Current: 250/201.9
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00

Abstract

An imaging system for measuring the field variance of distorted light waves collects a set of short exposure "distorted" images of an object, and applies a field variant data processing methodology in the digital domain, resulting in an image estimate which approaches the diffraction limited resolution of the underlying physical imaging system as if the distorting mechanism were not present. By explicitly quantifying and compensating for the field variance of the distorting media, arbitrarily wide fields can be imaged, well beyond the prior art limits imposed by isoplanatism. The preferred embodiment comprehensively eliminates the blurring effects of the atmosphere for ground based telescopes, removing a serious limitation that has plagued the use of telescopes since the time of Newton.

Claims

1. An optical system comprising:

an optical array detector;

a field stop;

a lenslet array interposed between the field stop and the optical array detector;

means coupled to the optical array detector for mensurating geometric distortion, said means further including means for determining, from said mensurated geometric distortion, optical wavefront distortions across a breadth of field angles as opposed to a single mono-axial field angle.

2. Apparatus including a focusing optic and a radiation sensor, the optic directing radiation from an object to the sensor, the sensor producing data signals corresponding thereto, the apparatus further including means responsive to data signals from the radiation sensor for characterizing geometrical distortion introduced by a medium between the object and the sensor even when, under isoplanatic conditions, the object is a zero contrast extended object.

3. An imaging method comprising:

receiving light from an object to be imaged, said light having been subject to optical wavefront distortions;

exposing an optical detector with said received light, the optical detector producing a plurality (M) of time-spaced sets of detector data therefrom, each corresponding to a two-dimensional image of said object;

processing said M time-spaced sets of detector data to discern geometric distortion of the received light;

determining, from said discerned geometric distortion, optical wavefront distortions of the received light across a breadth of field angles, as opposed to from a single mono-axial field angle; and

using the time-spaced sets of detector data and the determined optical wavefront distortions to produce a corrected set of image data.

4. The method of claim 3 which includes:

processing the detector data by computing a plurality of line integrals along straight lines through the corresponding two dimensional images to provide an approximation of the geometrical distortion therein; and

iteratively computing further line integrals along lines through the corresponding two dimensional images, said successive iterations making use of geometrical distortion approximated in preceding integrations to more closely follow distortion of a straight line in said image imposed by the geometrical distortion.

5. The method of claim 3 which includes:

processing the M time-spaced sets of detector data to produce a set of reference image data corresponding thereto;

for each of the M time-spaced sets of detector data;

globally searching for a geometrical distortion function which, when combined with said set of detector data to produce a set of compensated data, minimizes a difference between the set of compensated data and the reference image data.

6. The method of claim 3 which includes:

processing the M time-spaced sets of detector data to produce a set of reference image data corresponding thereto;

computing a radial line integral at uniform spacings through the reference image data;

computing a radial line integral at uniform spacings through each of said M time-spaced sets of detector data; and

using said computed radial line integrals in discerning the geometrical distortion.

7. The method of claim 3 which includes:

passing the received light through a lenslet array comprised of a plurality (N) of subapertures;

exposing the optical detector with light from the lenslet array, the optical detector producing N spatially-spaced sets of detector data therefrom, one for each of said subapertures, each of said N sets including M time-spaced sets of detector data; and

processing at least one of said N spatially-spaced sets of detector data to discern the geometric distortion of the received light.

8. The method of claim 7 which include processing each of said N sets of spatially-spaced detector data to discern geometric distortion of the received light.

9. Storage media containing a set of corrected image data produced in accordance with the method of claim 8.

10. Storage media containing a set of corrected image data produced in accordance with the method of claim 3.

11. The method of claim 8 which includes performing the processing and determining steps using a programmed computer workstation.

12. The method of claim 8 which further includes processing said sets of detector data to compensate for scintillation effects therein.

13. The method of claim 8 which includes:

processing said N sets of detector data by computing a plurality of line integrals along straight lines through the corresponding two dimensional images to provide an approximation of the geometrical distortion therein; and

iteratively computing further line integrals along lines through the corresponding two dimensional images, said successive iterations making use of geometrical distortion approximated in preceding integrations to more closely follow distortion of a straight line in said image imposed by the geometrical distortion.

14. The method of claim 8 which includes, for at least one of said N sets of spatially-spaced detector data:

processing the set of detector data to produce a set of reference image data corresponding thereto; and

globally searching for a geometrical distortion function which, when combined with the detector data to produce a set of compensated data, minimizes a difference between the set of compensated data and the reference image data.

15. The method of claim 14 which includes performing the steps thereof for each of said N spatially-spaced sets of detector data.

16. The method of claim 8 which includes, for at least one of said N sets of spatially-spaced detector data:

processing the detector data to produce a set of reference image data corresponding thereto;

computing a radial line integral at uniform spacings through the reference image data;

computing a radial line integral at uniform spacings through each of the N sets of spatially-spaced sets of detector data; and

computing differences between said computed radial line integrals to discern the geometrical distortion.

17. The method of claim 16 which includes performing the steps thereof for each of said N spatially-spaced sets of detector data.

18. A method of characterizing, in a plurality of dimensions, distortion introduced by a distorting medium interposed between an extended source and a detector, comprising:

receiving radiation from the extended source, said radiation having been subject to distortion by said medium;

exposing a detector with said received radiation, the detector producing a set of detector data therefrom corresponding to a two-dimensional representation of said source;

processing said set of detector data to discern geometric distortion of the received radiation;

determining, from said discerned geometric distortion, a three-dimensional turbulence structure of the distorting medium.

19. The method of claim 18 which includes:

passing the received radiation through a lenslet array of subapertures;

exposing the detector with radiation from the lenslet array, the detector producing a plurality of sets of detector data therefrom, each set corresponding to a two-dimensional representation of the extended source; and

processing said plurality of sets of detector data to discern said three dimensional turbulence structure.

20. In an imaging system including a focusing optic that directs radiation from an object to a sensor and provides a set of raw image data, an improvement including means coupled to the sensor for determining phase and geometric distortion in the raw image data across a breadth of field angles, as opposed to from a single mono-axial field angle.

21. The imaging system of claim 20 in which the imaging system is a telescope.