Temperature calibration of fast infrared scanners

A theoretical calibration function relating the electrical output of an airborne infrared scanner to the surface temperature of the scanned terrain is derived from radiometric principles. The function is applicable to scanners employing fast, photon-sensitive detectors, such as InSb and HgCdTe. Computed values of the function are used to plot a calibration curve for an idealized scanner of 8 to 14-micron bandwidth. A simple fourth-power law of the form AT to the fourth power + B can be fitted to the plotted curve with errors of less than 0.05 C over a 25-deg temperature range. The assumption of a T to the 4th power temperature dependence in thermal scanning at 8 to 14 microns is thereby justified on a theoretical basis. In addition, the temperature dependence of a fast infrared scanner is shown to be fundamentally different from that of a slow infrared radiometer of identical bandwidth.