Atmospheric Gas Absorption at DF Laser Wavelengths

The absorption of twenty-four DF laser wavelengths ranging from 3.6128 microm P(1)(6) to 4.0464 microm P(3)(11) was measured for CH(4) , N(2)O, CO(2), and HDO vapor. Total absorption was calculated for the lines for each of these absorbing gases and for the N(2) and H(2)O continua independently and collectively for two representative transmission paths (midlatitude summer model); i.e., a vertical path from sea level to the edge of the atmosphere containing 2.93 cm precipitable water and a horizontal 8.0-km path at sea level at 14.2-Torr water vapor partial pressure (11.2 cm precipitable water). Transmission was >90% for twelve lines in the vertical path and >65% for thirteen lines in the horizontal path. A comparison of the measured absorption coefficients was made with calculated values of McClatchey and Selby for seventeen lines. Good agreement was obtained with most lines, the worst within a factor ~2 of predicted values.