HAL: Humidity and Aerosol LIDAR for Profiling Atmospheric Water Vapor and Aerosols

摘要

The design and initial field testing of a prototype water vapor differential absorption LIDAR (DIAL) developed at the Air Force Research Laboratory are discussed in this paper. The operational version of a steerable LIDAR, named HAL (humidity and aerosol LIDAR), will profile line-of-sight aerosols and water vapor with high spatial and temporal resolution along downward-pointing, long-slant paths during clear-sky and moderately turbid conditions as a support tool for tactical high-energy laser experiments. A high pulse-energy alexandrite transmitter produces more than 1 W of narrow-line average power at the 729.23-nm H_(2)O vapor line, permitting high resolution using a modest receiver aperture. Stable transmitter operation for continuous periods exceeding 30 h has been demonstrated. The prototype LIDAR was pointed upward for direct and indirect comparisons of LIDAR-derived absolute humidity profiles with colocated and regionally launched radiosondes and with a colocated microwave radiometer. Qualitative (and often quantitative) agreement was observed for upward-pointing water vapor retrievals up to 4.5-km (3.5 km) altitudes during nighttime (daytime) hours, in addition to qualitative aerosol layer/cloud profiles up to 14 km. The H_(2)O vapor range will be expanded by a modified receiver currently being developed. Potential applications include characterizing the effects of water vapor and aerosols on high-energy electromagnetic wave propagation and cloud prediction.