Acoustooptic tunable filter performance in a staring IR sensor

The shape of the spectral transmittance of an acoustooptic tunable filter is invariant to a translation of the filter peak if the spectral transmittance is expressed as a function of wave number. A computer code based upon this invariance rapidly models the performance of an acoustooptic tunable filter operating as an integral part of a satellite-based earth-looking IR telescope. The telescope system detects moving IR-emitting sources against the background radiance of the earth. As an example, the problem of a source at 8 km with a water background is treated. It is shown that the effect of decreasing the filter interaction length is to increase the SNR, though an accompanying increase in background photons may saturate the detection process. The influence of atmospheric water vapor absorption is prominent in the results of analysis.