Optical EngineeringBandpass optimization for low-altitude long-path infared imaging
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Over relatively long paths near the earth's surface, atmospheric radiance can be a significant contributor to a poor SNR. These radiant emissions are primarily from atmospheric constituents such as H2O and CO2. Many commercially available IR imagers utilizing mercury-cadmium-telluride scanning detectors are not optimized for long horizontal path research. The degradation in the detected SNR due to atmospheric effects makes it advisable to use detectors that are sensitive in wavelength regions where the atmospheric attenuation is minimal. Through proper doping of the detector and cold finger filtering, there is an increase in the magnitude of the detected target radiance and a much more favorable ratio of target-to-path radiance that directly affects the image quality. We present a methodology that has resulted in a computer algorithm that is used to predict optimal system response conditions. Preliminary results show a 5% to 10% enhancement of the target-to-background apparent temperature or ΔT in the 8- to 12-μm region over a relatively short path.