Infrared Measurements of Atmospheric Transmission at Sea Level

Atmospheric transmittance spectra from 0.56 μ to 10.7 μ, obtained over a 25-km horizontal path at sea level, are presented. The sources were six 150-cm diam carbon arc searchlights. A radiometrically calibrated spectrometer equipped with a NaCl prism and a thermocouple detector was used to record the spectral distribution of the radiation transmitted through the atmosphere. The transmittance spectra were obtained for values of precipitable water vapor ranging from 21.5 cm to 43.3 cm. From these spectra the selective transmittance of four atmospheric windows was measured. A plot of selective transmittance as a function of the square root of the precipitable water vapor for the four windows shows that the transmittance in these windows is well described by the statistical model of band absorption.