Lidar Extinction Methods Applied to Observations of Obscurant Events

摘要

The SRI four-wavelength (0.53-, 1.06-, 3.8-, and 10.6-micrometers) lidar system was used during the Smoke Week VI/SNOW-TWO field experiments to collect data for analysis of obscurant extinction distributions. Basically, laser pulses at the four wavelengths were transmitted along a horizontal path terminated at a distance of 600 m from the lidar by a target of uniform reflective properties. The laser pulses at each wavelength were emitted sequentially along the same path within a 60-micrometer interval to reduce effects of time- and space-varying aerosol concentrations on each four-wavelength pulse set. About 60 pulse sets were transmitted for each minute of operation. Both energy backscattered from atmospheric aerosols and energy reflected from the solid target were collected within a telescope and directed to appropriate detectors using dichroic filters. After logarithmic amplification, backscatter signatures were digitized by an 8-bit 100-MHz transient recorder, and the resulting digital records were stored on nine-track magnetic tape for subsequent analysis. Obscurant aerosols were generated upwind of the lidar/target path, and lidar observations were initiated just before the obscurants interesected the viewing path. Other details of the lidar system and its applications to the Smoke Week VI/SNOW-TWO field test have been presented elsewhere. (Reprints)