Optical non-uniformity correction (NUC) for active mode imaging sensors

• US 9,473,768 B2
• Filed: 09/03/2014
• Issued: 10/18/2016
• Est. Priority Date: 09/03/2014
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Uyeno, Gerald P., Keller, Sean D., Acton, David D.
• Primary Examiner(s): Natnael, Paulos M
• Assistant Examiner(s): Khalid, Omer
• Application Number:
  US14/476,199
• Publication Number:
  US 20160065956A1
• Time in Patent Office: 776 Days
• Field of Search: 348/67, 348/68, 348/E9.206
• US Class Current: 1/1
• CPC Class Codes: A62B 1/04 Single parts, e.g. fastening devices
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/56 provided with illuminating means
• CPC Class Codes: H04N 25/63 applied to dark current

Abstract

Optical non-uniformity correction (NUC) of an active mode image sensor scans a spot over a portion of the sensor'"'"'s FOV within a frame time so that the net response of the sensor is approximately uniform. Scanning the laser spot simultaneously performs the NUC and provides the illumination of the FOV for imaging the scene. The laser spot is suitably scanned in an overlapping geometrical pattern relative to a line-of-sight of the sensor'"'"'s imager while modulating a spacing between overlapping laser spots, the size of the spot, a dwell time of the laser spot or the energy of the laser spot or combinations thereof as a function of the scan position of the laser spot so that the laser illumination is inversely proportional to the imager response at the scan position of the laser spot. A liquid crystal waveguide may be used to form and scan the small laser spot over the FOV within the frame time.

Claims

1. A method of optical non-uniformity correction (NUC) of an active mode imaging sensor having a non-uniform response over a field-of-view (FOV), the method comprising:

transmitting a laser spot that is smaller than the sensor'"'"'s field of view (FOV);

scanning the laser spot over a portion of the FOV; and

modulating as a function of the scan position of the laser spot a spacing between overlapping laser spots, a size of the laser spot, a dwell time of the laser spot or the energy of the laser spot or combinations thereof so that the laser illumination is inversely proportional to the response of the imaging sensor at the scan position of the laser spot to correct for the sensor'"'"'s non-uniform response over the scanned portion of the FOV.

2. The method of claim 1, wherein the laser spot is scanned over the portion of the FOV in a frame time, further comprising:

reading out a NUC'"'"'d image from the sensor at each frame time.

3. The method of claim 1, wherein the sensor comprises a laser illuminator that generates the laser spot, a pixelated imager and optics having an entrance pupil, wherein the laser spot illuminates a portion of a scene thereby forming an approximately Lambertian point source at an angle of incidence to the entrance pupil, whereby a response of the pixelated imager falls off approximately as the 4^th power of the cosine of the angle of incidence, wherein the laser spot is scanned over the FOV so that the laser illumination is inversely proportional to the response of the pixelated imager at the scan position of the laser spot.

10. The method of claim 1, wherein the size of the laser spot is less than 25% of the FOV.

11. The method of claim 1, further comprising scanning the laser spot to increase the SNR in a local region of the FOV.

12. The method of claim 1, wherein the sensor comprises a pixelated imager having fixed pattern noise, comprising forming the laser spot with the size of an individual pixel and scanning the laser spot to compensate for the fixed pattern noise in a local region of the FOV.

13. The method of claim 1, wherein the scanned portion of the FOV is less than the entire FOV.

4. The A method of optical non-uniformity correction (NUC) of an active mode imaging sensor having a field-of-view (FOV), wherein the sensor comprises a laser illuminator that generates a laser spot, a pixelated imager and optics having an entrance pupil, wherein the laser spot illuminates a portion of a scene thereby forming an approximately Lambertian point source at an angle of incidence to the entrance pupil, whereby a response of the pixelated imager falls off approximately as the 4^th power of the cosine of the angle of incidence, the method comprising:

transmitting a laser spot that is smaller than the sensor'"'"'s field of view (FOV);

scanning the laser spot over a portion of the FOV so that a net response of the sensor is uniform over the scanned portion of the FOV, wherein the laser spot is scanned in an overlapping geometrical pattern relative to a line-of-sight of the imager over the FOV within a frame time while modulating as a function of the scan position of the laser spot a spacing between overlapping laser spots, a size of the laser spot, a dwell time of the laser spot or the energy of the laser spot or combinations thereof so that the laser illumination is inversely proportional to the response of the pixelated imager at the scan position of the laser spot.

5. The method of claim 4, further comprising controlling a liquid crystal waveguide to form laser energy into the laser spot and to scan the laser spot over the FOV within the frame time.

6. The method of claim 5, wherein the liquid crystal waveguide comprises a core and at least one cladding, liquid crystal material within said at least one cladding and at least one electrode and a ground plane on opposite sides of the liquid crystal material, wherein controlling the LCWG comprising applying at least one time-varying voltage to the at least one electrode to vary an electric field to induce said liquid crystal material to form a time-varying refractive shape to form and scan the laser spot over the FOV.

7. A method, of optical non-uniformity correction (NUC) of an active mode imaging sensor having a field-of-view (FOV), wherein the sensor comprises a laser illuminator that generates the laser spot, a pixelated imager and optics having an entrance pupil, wherein the laser spot illuminates a portion of a scene thereby forming an approximately point source at an angle of incidence to the entrance pupil, whereby a response of the pixelated imager falls off as a function of an increasing angle of incidence, the method comprising:

transmitting a laser spot that is smaller than the sensor'"'"'s field of view (FOV);

scanning the laser spot over a portion of the FOV so that the laser illumination is inversely proportional to the response of the pixelated imager at the scan position of the laser spot so that a net response of the sensor is uniform over the scanned portion of the FOV.

8. A method of optical non-uniformity correction (NUC) of an active mode imaging sensor having a field-of-view (FOV), the method comprising:

transmitting a laser spot that is smaller than the sensor'"'"'s field of view (FOV);

scanning the laser spot over a portion of the FOV in an overlapping geometrical pattern relative to a line-of-sight of the imager over the FOV within a frame time while modulating as a function of the scan position of the laser spot a spacing between overlapping laser spots, a size of the laser spot, a dwell time of the laser spot or the energy of the laser spot or combinations thereof so that a net response of the sensor is uniform over the scanned portion of the FOV.

9. A method of optical non-uniformity correction (NUC) of an active mode imaging sensor having a field-of-view (FOV), wherein the sensor comprises a liquid crystal waveguide having a core and at least one cladding, liquid crystal material within said at least one cladding and at least one electrode and a ground plane on opposite sides of the liquid crystal material, the method comprising:

transmitting a laser spot that is smaller than the sensor'"'"'s field of view (FOV);

applying at least one time-varying voltage to said at least one electrode to vary an electric field to induce said liquid crystal material to form a time-varying refractive shape to form and scan the laser spot over a portion of the FOV so that a net response of the sensor is uniform over the scanned portion of the FOV.