Radiometric calibration of infrared cameras accounting for atmospheric path effects

Radiometric infrared camera systems are most often used to characterize the IR signature of targets (often an aircraft or rocket) through significant air paths that reduce the received signal. Tactical targets can be imaged at standoff distances up to 1000km or more, but there are many cases where the target is within 1km range, as is the case with a close-in flyby at a test range. This paper compares experimental radiometric data to a theoretical model of the atmosphere. The radiometric data was collected in the 3-5 micron band using an indium antimonide staring-array camera and long focal length lens combined with radiometric analysis software. The system was calibrated to measure target radiances, but can also be used to estimate target temperatures in cases where the in-band target emissivity is well understood. The radiometric data are compared to a model built on MODTRAN code, with conclusions about the attenuation introduced by the atmosphere for standard medium-range imaging systems in “typical” observing conditions.