Advanced FTIR Spectral Measurements of Low Contrast Rotorcraft Targets

Spectral infrared (IR) signature measurements are vital to determining and enhancing the survivability of a military rotorcraft against IR seeking missiles. Survivability calculations require using spectral IR signature data, as opposed to band-integrated IR signature data, because with spectral data, one can account for the wavelength-dependent effects, such as atmospheric transmittance, target reflectance, and threat response. However, accurately measuring the spectral signature of a helicopter presents many challenges. Errors on the order of 100% are often the result of such measurements. In contrast, the IR signature measurement efforts made by Bell Helicopter Textron Incorporated (BHTI) have been quite successful. Measurements of laboratory standards at BHTI have exhibited an uncertainty of less than 2%. In the field, processed spectral measurements have agreed well with data generated independently by other radiometric instruments. This paper presents Bell Helicopter's spectral IR signature measurement technique, including the procedure, selection of equipment, sources of error, and some unclassified results.