Calibration of a satellite infrared radiometer

The calibration procedure is described for a two-channel imaging radiometer on board the Heat Capacity Mapping Mission, a single sensor satellite in a near polar orbit. The Heat Capacity Mapping Radiometer measures radiation temperature and reflectivity with an instantaneous FOV of 600 m and a noise equivalent temperature of 0.4 K at 280 K in the thermal IR channel. Unexplained changes in the system during satellite launch were treated through comparison with surface/atmosphere data to force agreement. This necessitated an offset from the prelaunch calibration by 5.5 K. Later comparisons showed no difference. Possible explanations are described.