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.

Abstract: Described herein is a method and apparatus for calibrating an infrared camera at elevated temperatures using a reference surface. The method comprises selecting a normal well-fill condition for pixels in the camera in accordance with normal operating temperatures and stare time (30, 32, 34), using the normal well-fill condition to calculate a selected stare time/surface temperature combination for which selected non-uniform calibration coefficients are determined (36, 38), adjusting and re-adjusting the stare time/surface temperature to obtain adjusted and re-adjusted non-uniform calibration coefficients respectively (40, 42, 44, 46), and determining final non-uniform calibration coefficients for the camera using the selected, adjusted and re-adjusted non-uniform calibration coefficients (48).