Lidar observations at 0.7-micrometers and 10.6-micrometers wavelengths during dusty infrared test I (DIRT I)

This technical report describes lidar measurements and results using a 10.6 micrometers lidar and the Mark 9 (0.7 micrometers) lidar systems during the Dusty Infrared Test I (DIRT I). Transmission comparisons are made between the two wavelengths with artillery barrages, TNT explosions, and oil/rubber fire-generated dust and smoke clouds in a test zone midway (1 km) along the lidar path. A target at the end of the lidar path provided a reference backscatter return for the transmission measurements. Backscatter properties of the dust and smoke clouds are also discussed. Results of the DIRT I program indicate that the broad particle size distribution present in the dust generated produced little if any wavelength dependent transmission effects. The few observed exceptions where greater 10.6 micrometers transmission is indicated generally can be explained by the presence of wavelength-dependent smoke along the optical path, which is also generated by the detonations. Backscatter-to-transmission relationships are grossly related but, in general, are quite nonlinear, as can be expected when multiple and specular scatter by the large particles, as well as strong attenuations, are involved. The oil/rubber fire generated dense black smoke that was totally opaque to the 0.7 micrometers lidar, while the 10.6 micrometers transmission measurements indicate a worse-case transmission of approximately 6%.