PNNL

Abstract

The performance of a prototype water vapor differential absorption lidar (DIAL) is evaluated. This compact, eye-safe, diode-laser-based prototype was developed by Vaisala. It was designed to operate unattended in all weather conditions, providing height-resolved measurements of water vapor mixing ratio from the surface up to 3 km or cloud base, whichever is lower. Evaluation of the Vaisala prototype was carried out at the US Department of Energy’s Atmospheric Radiation Measure site in north-central Oklahoma (i.e. the Southern Great Plains site) from 15 May to 12 June 2017. DIAL measurements were compared to observations from radiosondes that were launched within 200m of the DIAL’s location. Radiosonde measurements are also compared to observations from a collocated Raman lidar and an Atmospheric Emitted Radiance Interferometer ( AERI). During the evaluation period, the DIAL operated continuously and did not experience any failures or malfunctions. The data availability was greater than 90 % below 900 m, but dropped below 50 % at heights above 1200 m. Based on 106 radiosonde profiles, the mean difference between the DIAL and the radiosonde was -0.01 g kg-1 , with a standard deviation of 0.68 g kg-1, and a linear correlation coefficient of 0.98. For comparison, the mean difference between the Raman lidar and the radiosonde was 0.04 g kg-1, with a standard deviation of 0.61 g kg-1, and a linear correlation coefficient of 0.99.