ON-BOARD NON-UNIFORMITY CORRECTION CALIBRATION METHODS FOR MICROBOLOMETER FOCAL PLANE ARRAYS

• US 20120211648A1
• Filed: 02/11/2012
• Published: 08/23/2012
• Est. Priority Date: 02/21/2011
• Status: Active Grant

• Current Assignee: Safran Defense and Space Incorporated
• Original Assignee: Vectronix Inc. (Safran SA)
• Inventors: LINSACUM, DERON L., Lavik, Nils A., Kwan, Greg
• Granted Patent: US 9,167,179 B2
• Time in Patent Office: Days
• US Class Current: 250/252.1
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 2005/106 Arrays
• CPC Class Codes: G01J 2005/202 Arrays
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52
• CPC Class Codes: G01N 2201/1211 for temperature
• CPC Class Codes: G01N 2201/12707 Pre-test of apparatus, e.g. dark test, sensor test
• CPC Class Codes: G01N 2201/12715 Zero adjustment, i.e. to verify calibration
• CPC Class Codes: G01N 2201/12746 Calibration values determination
• CPC Class Codes: G01N 2201/12753 and storage
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

On-board non-uniformity correction calibration methods for a microbolometer focal plane array in a thermal camera are disclosed. The methods include performing first calculations in the processor unit of the thermal camera to generate and apply a set of coarse correction bias voltages to the detector elements. The method also includes performing calculations in the external computer based on image data collected by the thermal camera with the coarse correction bias voltages applied to the detector elements to generate a set of fine correction bias voltages. The method also includes downloading the fine correction bias voltages to the thermal camera and applying the fine correction voltages to the detector elements to establish a fine calibration of the microbolometer focal plane array.

Claims

1. A method of calibrating a microbolometer focal plane array (MFPA) having detector elements and that resides in a thermal camera that has a processing unit that is operably coupled to an external computer, comprising:

a) determining reference and detector non-uniformity corrections (NUCs) in the processing unit based on reference voltages from the MPFA, and applying the reference and detector NUCs to the detector elements as coarse corrections that establish a coarse calibration, and sending the reference and detector NUCs to the external computer;

b) in a first measurement step, collecting image data DL1 and DH1 at respective first ambient and first calibration temperatures, and collecting image data DL2 and DH2 at respective second ambient and second calibration temperatures, and sending image data DL1, DH1, DL2 and DH2 to the external computer;

c) calculating in the external computer fine corrections based on the collected image data DL1, DH1, DL2 and DH2 and the reference and detector NUCs; and

d) sending the fine corrections from the external computer to the processor unit and applying the fine corrections to the detector elements to establish a fine calibration.

2. The method of claim 1, wherein calculating the fine corrections in the external computer further comprises calculating from collected image data DL1, DH1, DL2 and DH2 gain values based on a gain slope and a gain intercept, and calculating offset values based on an offset slope and an offset intercept.

3. The method of claim 1, wherein the first and second ambient temperatures differ by a temperature increment δ

T, and wherein the first and second calibration temperatures differ by the temperature increment δ

T.

4. The method of claim 3, wherein δ

T=4°

C.

5. The method of claim 1, further comprising repeating acts a) through d) therein for additional measurement steps that sequentially increment the first and second ambient temperatures and the first and second calibration temperatures by a temperature increment δ

T.

6. The method of claim 1, wherein the reference and detector NUCs are defined by a six-bit numbers for each detector element, wherein the first bit is a sign bit and the remaining five bits define a 0 to 32 bias voltage increment.

7. The method of claim 1, wherein the first and second calibration temperatures are maintained about 20°

C. higher than the first and second ambient temperatures, respectively.

8. A method of calibrating a microbolometer focal plane array (MFPA) having detector elements and that resides in a thermal camera that has a processing unit that is operably coupled to an external computer, comprising:

performing first calculations in the processor unit to generate a set of coarse correction bias voltages, and applying the coarse correction bias voltages to the detector elements;

performing calculations in the external computer based on image data collected by the thermal camera with the coarse correction bias voltages applied to the detector elements to generate a set of fine correction bias voltages; and

downloading the fine correction bias voltages and applying the fine correction voltages to the detector elements to establish a fine calibration of the MFPA.

9. The method according to claim 8, wherein performing the first calculations includes determining reference and detector non-uniformity corrections (NUCs).

10. The method according to claim 8, wherein performing the second calculations includes calculating gain and offset values based on image data collected at four different temperatures.