Simultaneous ground-based remote sensing of water vapor by differential absorption and Raman lidars

Abstract

Uncertainties in the absolute calibration of the water vapor measurements are currently the limiting factor in the improvement of radiative transfer algorithms for clear skies. While instruments such as the microwave radiometer can provide accurate measurements of total precipitable water vapor in the column, accurate profiles of water vapor are also needed in order to calculate accurate cooling rate profiles. Raman lidar and differential absorption lidar (DIAL) are presently the most advanced techniques to measure the vertical distribution of water vapor in the atmosphere with both high temporal and vertical resolution and accuracy. Therefore, it is important to perform a dedicated experiment to assess the performance of both systems, with respect to accuracy, resolution, and available range. A secondary goal of this experiment was to better characterize the operational Raman lidar at the ARM Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site in north central Oklahoma. The water vapor DIAL from the Max-Planck Institute (MPI) for Meteorology in Hamburg, Germany was collocated with the Raman lidar from 29 September - 19 October 1999. The two systems were located about 15 m apart, and more than 100 h of coincident data was collected during both daytime and nighttime. Radiosondes, which were launched from the CART site every three hours during this experiment, and co-located microwave radiometer data are also used in this study.