Calibration of infra red cameras
AssigneeSelex Sensors and Airborne Systems Limited
InventorsNorman Frederick Watson, Michael Grant McGuigan
Life of this patent
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Abstract
A reference surface for calibrating cooled infra red detectors includes a plurality of corner cube units which reflect radiation incident directly on them. The surface of each corner cube unit is partially reflective and partially emissive such that, when imaged by a cryogenically cooled detector, the reference surface appears as a black body source at a lower temperature than the actual temperature thereof.
Claims11
A calibration system for an infrared detector comprising a plurality of detector elements, said calibration system comprising:
- a reference surface which includes a plurality of concave corner cubes that are partially reflective and partially emissive;
- temperature controlling means adapted to maintain the reference surface at a desired calibration temperature;
- and
- processing means for receiving an output signal generated by an infrared detector at said the desired calibration temperature, comparing said detector output signal for each element of said detector with a predetermined ideal output signal for said desired calibration temperature and calculating a calibration coefficient based on the difference between the detector output signal and the ideal output signal at said desired calibration temperature.
A method of calibrating an infrared detector comprising a plurality of detector elements using a reference surface that is characterized by partial emissivity and partial reflectivity, the method comprising:
- a) presenting the reference surface at a known temperature to an infrared detector;
- b) measuring the output of each detector element;
- c) comparing the measured output of each detector element with a nominal output for the known reference surface temperature to determine a calibration error at the known temperature;
- and
- d) heating the reference surface to one or more further known temperatures and repeating steps b) and c) to determine a calibration error for each of the further known temperatures.
Dependencies are inferred from the claim text.