Pure Rotational Raman Lidar for Temperature Measurements in the Lower Troposphere
Document ID: 96
Doctoral Dissertation
The Pennsylvania State University
The Graduate School
Department of Electrical and Computer Engineering
Abstract
An examination into the use of the pure rotational Raman spectrum for lidar measurements of lower tropospheric thermal structure has been made. This technique was chosen because it showed potential for making measurements on short spacial and temporal scales. To determine if the rotational Raman technique may be extended down through the boundary layer, it was necessary to calculate the absolute intensities of water vapor's pure rotational Raman quantum lines, to establish design configurations for an ideal optical detector, to parameterize different analysis techniques for obtaining temperature versus lidar rotational ratio conversion curves, and to evaluate possible means of filtering lidar temperature data. Results showed that for an atmosphere containing 3 % water vapor at 320 K, and a detector system using a 0.2 nm bandwidth filter, water vapor contributed less than 0.1 % (- 0.2 K error) of the total backscattered signal for filter placements less than 163.9 cm-1 from the primary laser frequency For filters with 3 nm bandwidths, filter placements need to be less than 224.2 cm-1. Ideal filter configurations were calculated to reside at 30.1 cm-1 with a 17.7 cm-1 bandwidth and at 140.6 cm-1 with a 75.3 cm-1 bandwidth. Filtering temperature profiles using an optimal estimation algorithm, based on balloon climatology data, was shown to work as well as, if not better, than general weighted average filters. The filtered data show temperature standard deviations less than 0.8 K at altitudes below 7 km with a minimum of 0.3 K at 1 km. It was determined that the rotational Raman technique provides a useful and powerful method to measure profiles of atmospheric temperature in the lower troposphere, even in the presence of light to moderate backgrounds of haze, fog, and clouds.
| Citation: | P. A. T. Haris, "Pure Rotational Raman Lidar for Temperature Measurements in the Lower Troposphere", The Pennsylvania State University, Doctoral Dissertation, August 1995, 170 pages |