LASE (Lidar Atmospheric Sensing Experiment)

The LASE detector system consists of two silicon avalanche photodiodes (Si:APD) and three digitizers to cover a large signal dynamic range (106), and the signal processor system is designed to be relatively insensitive to rapid changes in signal levels. The LASE data system on the DC-8 will enable real-time and post-flight analyses on-board the aircraft. A 275 MHz Alpine w/DEC Alpha CPU with 128 MB memory 12 GB data storage is used for data processing and analysis Adjustments to the instrument will be made on-board the aircraft using on-board test equipment to maintain optimum performance.

In the current mode of operation LASE operates locked to a strong water vapor line and electronically tunes to any spectral position on the absorption line to choose the suitable absorption cross-section for optimum measurements over a range of water vapor concentrations in the atmosphere. In addition, LASE can operate over two or three water vapor concentration regions to cover a large altitude region in the troposphere. This unique method of operation permits rapid and more flexible absorption cross-section selection capability for water vapor measurements over the entire troposphere in a single pass. Water vapor measurements using this new method have been implemented and tested during the LASE validation experiment in September 1995.

During the September 1995 LASE Validation Field Experiment, LASE measurements were compared with a number of in-situ and remote sensors from the ground and other aircraft (Browell et al., 1997). During the Validation Experiment LASE demonstrated the capability to measure water vapor distributions over the entire troposphere with values ranging from about 15 g/kg near the ocean surface to about 0.01 g/kg near the tropopause in the tropical region and at mid-latitudes. The LASE water vapor measurements were found to have an accuracy of better than 6% or 0.01 g/kg, whichever is greater, across the entire troposphere. The projected water vapor and aerosol measurement capabilities of LASE during the SOLVE mission are listed in Table 1.