ATMOSPHERIC TRANSMISSION IN THE 2.8-5.5-MU-M REGION - DESCRIPTION OF THE FOURIER INTERFEROMETRIC TRANSMISSOMETER AND TYPICAL RESULT AT LOW-TEMPERATURES

A study of moderate resolution (1 cm-1) atmospheric transmission measurements made over a 5.7-km path and under a wide range of temperatures and humidities is presented. A description of the Fourier interferometric transmissometer (FIT) used for this study and a detailed analysis of the experimental protocol developed for that type of instrument are given. Results for the 2.8-5.5-1m spectral window are compared to calculations using the LOWTRAN6 and FASCOD2 transmission codes. We examine the accuracy with which these codes predict transmittance in spectral domains (1800-2000 and 3200-3500 cm-1) strongly affected by water vapor concentration. Preliminary analysis, indicates that although LOWTRAN6 predicts well the summer transmittance (+30.3° C) there are significant divergences for the winter case (—21.4° C). The comparison of FASCOD2 with experimental results shows much closer agreement than LOWTRAN6 for both summer and winter cases. © 1990 Optical Society of America.