ATMOSPHERIC TRANSMITTANCE MEASUREMENTS OF ND-YAG IODINE AND CO2-LASERRADIATION OVER 8.6-KM AND STATISTICAL-ANALYSIS OF EXTINCTION COEFFICIENTS

A long-range multiwavelength laser transmissometer for measuring atmos pheric extinction of iodine laser radiation (1.315 mu m), simultaneous ly with Nd:YAG (1.06 mu m) and CO2 (10.6 mu m) laser radiation was des igned, built and operated under different atmospheric conditions, over a distance of 8.6 km in hilly terrain near Tubingen, Germany. Beam ex tinction was obtained by measuring the ratio of the total laser radiat ion to the total received radiation as collected by a mirror and focus ed onto a pyroelectrical detector array. Measured values of laser exti nction were compared with model predictions (FASCODE 3P) based on simu ltaneously measured meteorological data as model input parameters. The agreement was found to be very good. It is shown that the atmospheric extinction coefficient of iodine laser radiation cen be predicted to a good approximation by a linear equation containing the extinction co efficients of Nd:YAG and CO2 laser radiation. Statistical analyses of atmospheric laser extinction coefficients are presented for these lase r wavelengths. Scatter diagrams of extinction coefficients are present ed for the summer and winter season together with an analysis of the a nnual variability. The iodine laser, if compared to the CO2 laser, sho ws advantage in molecular extinction which is, however, overcompensate d by aerosol extinction being often more than two orders of magnitude larger for iodine laser than for CO2 laser radiation.