Methods and apparatus for remotely sensing the orientation of an object

• US 5,811,826 A
• Filed: 02/07/1997
• Issued: 09/22/1998
• Est. Priority Date: 02/07/1996
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Shirley, Lyle G.
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US08/797,530
• Time in Patent Office: 592 Days
• Field of Search: 250/559.29, 250/559.3, 250/559.37, 356/28, 356/27, 356/28.5, 356/375, 73/861.06, 364/604, 364/728.03, 364/728.06
• US Class Current: 250/559.29
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46

Abstract

A method and apparatus for remotely sensing the orientation of an object takes advantage of the fact that, for flat surfaces, a change in radiation frequency illuminating the object produces a global translation at the detector plane of the speckle pattern reflected from the object. An object is illuminated with radiation of two different frequencies and the corresponding speckle patterns are compared to determine the magnitude and direction of shift from the first speckle pattern to the second. The magnitude and direction of the speckle pattern shift indicates the orientation of the object.

Claims

1. A method for remotely sensing the orientation of an object, the method comprising:

(a) receiving a first speckle pattern produced by radiation of a first frequency reflected from the object;

(b) receiving a second speckle pattern produced by radiation of a second frequency reflected from the object; and

(c) determining the differences between the second speckle pattern and the first speckle pattern.

2. The method of claim 1 further comprising the steps of:

illuminating the object with radiation of a first wavelength before step (a); and

illuminating the object with radiation of a second frequency before step (b).

3. The method of claim 2 wherein said illumination steps occur simultaneously.

4. The method of claim 2 wherein steps (a) and (b) occur simultaneously.

5. The method of claim 1 wherein steps (a) and (b) occur simultaneously.

6. The method of claim 1 wherein step (c) comprises cross-correlating the second speckle pattern and the first speckle pattern.

7. The method of claim 1 wherein step (c) comprises determining the direction the second speckle pattern has shifted from the first speckle pattern.

8. The method of claim 1 wherein step (c) further comprises determining the direction the second speckle pattern has shifted from the first speckle pattern and the magnitude of the shift.

9. An apparatus for remotely sensing the orientation of an object comprising:

a speckle pattern receiver which receives a first speckle pattern corresponding to radiation of a first frequency reflected from the object and a second speckle pattern corresponding to radiation of a second frequency reflected from the object; and

a processor in electrical communication with said speckle pattern receiver, said processor comparing the second speckle pattern to the first speckle pattern to determine the differences between for the second speckle pattern and the first speckle pattern.

10. The apparatus of claim 9 further comprising a radiation source illuminating the object with radiation at a first frequency and a second frequency.

11. The apparatus of claim 10 wherein said radiation source comprises a laser capable of operating at more than one frequency.

12. The apparatus of claim 9 further comprising a first radiation source illuminating the object with radiation at a first frequency and a second radiation source illuminating the object with radiation at a second frequency.

13. The apparatus of claim 9 wherein said speckle pattern receiver is a charge coupled device.

14. The apparatus of claim 9 wherein said processor cross-correlates said first speckle pattern and said second speckle pattern.

15. The apparatus of claim 9 wherein said processor compares the second speckle pattern to the first speckle pattern to determine the direction the second speckle pattern has shifted from the first speckle pattern and the magnitude of the shift.

16. The apparatus of claim 9 further comprising a lens between said speckle pattern receiver and the object.

17. The apparatus of claim 16 wherein said speckle pattern receiver and said lens are spaced apart by a distance equal to the focal length of said lens.

18. An apparatus for remotely sensing the orientation of an object, the apparatus comprising:

a radiation source alternately illuminating the object with radiation at a first frequency and a second frequency;

a speckle pattern receiver which receives a first speckle pattern corresponding to radiation of said first frequency reflected from the object and a second speckle pattern corresponding to radiation of said second frequency reflected from the object; and

a processor in electrical communication with said speckle pattern receiver, said processor comparing the second speckle pattern to the first speckle pattern in order to determine the direction the second speckle pattern has shifted from the first speckle pattern and the magnitude of the shift.

19. The apparatus of claim 18 further comprising a lens between said speckle pattern receiver and the object, said speckle pattern receiver and said lens spaced apart by a distance equal to the focal length of said lens.