System and environmental conditions that impact an imaging system's optical transfer function (OTF)

In the analysis of scene content of an infrared (IR) imager the optical transfer function (OTF) must be determined. For broadband systems the OTF is dependent upon the optics detector response and source spectral characteristics. For an IR imaging system with a 15.24 cm diameter Cassegrain telescope and 5.08 cm diameter central obscuration, the OTF can readily be approximated for monochromatic scene radiation. The spectral conditions of interest are those of a hot blackbody (BB) source to that of one at ambient temperature. The differing system conditions of interest are those of a filtered IR detector versus an unfiltered detector for the 8 - 12 micrometers spectral region. The environmental conditions of interest are those of dry versus humid atmospheres. For humid atmospheres the filtered detector has a distinct sensitivity advantage in that it can block out undesired path radiance from atmospheric constituents that would decrease the signal to noise ratio. For a dry atmosphere the unfiltered detector would have an advantage in that it would have a wider spectral response and receive more of the emitted source radiation yielding better spatial resolution near high frequency cutoff.