Remote Sensing of the Optical and Physical Densities of Smoke, Dust, and Water Clouds

A new van-mounted four-wavelength lidar system designed for remote aerosol characterization has been constructed and tested. The most important design criteria established for the new systems was that the laser pulses should view the same path and be emitted in a minimal time period in order to reduce effects of time-variant aerosol distributions on multiple-wavelength observations. Energy at 0.53-and 1.06 micro m wavelengths is transmitted into the atmosphere using a Nd:YAG laser; 3.8 micro m is transmitted using a DF laser, and 10.6 micro m is transmitted using a CO2 laser. An optical arrangement provides for transmitting the pulses along the same horizontal path, coaxial with a 12-inch-diameter Newtonian telescope. Wavelength-separation optics direct received energy to separate detectors for 0.53-and 1.06 micro m energy and to a common detector for 3.8- and 10.6 micro m energy. By deriving both 0.53-and 1.06 micro m laser emissions from a single flash lamp excitation, and by recording the four backscatter signatures within a single transient digitizer 2048-word record, the four signatures can be collected within a 160-micro m interval. Each four-wavelengths lidar record is transferred to an LSI 11/2 microcomputer and written on none-track magnetic tape, together with date and time information. SRI conducted a field test of the four-wavelength lidar to evaluate system performance in an environment similar to that of previous lidar operations at Army range facilities. The lidar van was located about 600 m from an 8-ft square passive reflector.