■Vvv^M 



10 12 



WAVELE^4GTH IN MICRONS 



Figure 4. Transmission of Atmosphere (Sea Level, 1000 Feet 

 Path, 0.1 cm Precipitable Water) 



practical matter, we must accept a spectral passband obtainable from practical, reliable 

 filters. The filters in the Barnes Infrared Thermometer are Indium Antimonide, which 

 passes wavelengths longer than 8fi , and Kodak Irtran-2, which transmits all radiations 

 shorter than 14 /z ; the spectral passband is thus 8 m to 14 /^ , An alternative choice would 

 have been Indium Antimonide and Arsenic Trisulfide, which cuts off at 12 ^ , Unfortunately, 

 the transmissivity or transmdssion efficiency of Arsenic Trisulfide is rather low and the 

 signal receivable by the detector with this choice would have been considerably lower, re- 

 sulting in more noise in the instrument output than is obtained with the Indium Antimonide 

 — Irtran-2 combination. Figure 5 shows the spectral passband of the Barnes Infrared 

 Thermometer. 



WAVELENGTH 



Figure 5. Spectral Passband of Barnes Infrared 

 Thermometer, Model IT-2 



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