Lower Tropospheric Temperature Measurement Scheme for an Advanced Lidar Atmospheric Profiling System
Document ID: 110
Master's Thesis
The Pennsylvania State University
The Graduate School
Department of Electrical Engineering
Abstract
LIght Detection And Ranging (LIDAR) systems can be used to sense atmospheric properties from a remote distance. The basic Raman lidar technique is to transmit a specific frequency of laser radiation into the sky, and collect the returned vibrational and rotational Raman-shifted frequencies with a telescope. By then separating and processing the return wavelengths associated with specific molecules, near real-time profiles of atmospheric properties can be obtained. Temperature measurement using this method was first suggest by Cooney [1972], and has since been examined by a number of groups. Current capabilities of lidar to measure temperature and other major properties of the lower atmosphere rival those of the antiquated and costly radiosonde method. The Lidar Atmospheric Profile Sensor (LAPS) is an optical remote sensing system developed at Penn State Univerisity for vertical profiling of lower tropospheric RF refractivity from aboard U.S. Navy ships. The system was demonstrated in late 1996, and has since been used in a number of atmospheric studies. The need for a variety of system performance modificaitons, noted during various field studies utilizing LAPS, has been observed and work toward an Advanced LAPS (ALAPS) is now underway. The design of the temperature measurement scheme presented here was seen as a second step toward the ALAPS system, the first step having been an upgrade in the electronics control system by Achey [2002]. As was shown, the capability of measuring atmospheric temperature is a significant factor in determining RF refractivity gradients. The design of a laser-based system to do this requires careful consideration of the safety of personnel working near or directly on the instrument after it has been deployed. The ability to measure atmospheric temperature with an eye-safe, ultraviolet transmission wavelength of 355 nm was examined for this reason. Selection of optical components and specification of the test setup to be used for daytime and nighttime profiling of lower tropospheric temperature, utilizing the LAPS system in a slightly modified form, has been done. A comparison of regression techniques for processing lidar rotational Raman temperature data is also given. This comparison showed agreement between calibration done with the instrument’s theoretical temperature sensitivity curve and calibration with a radiosonde with the advantage that the theoretical curve provides better extension of the applicable range of profile temperatures.
| Citation: | C. T. Slick, "Lower Tropospheric Temperature Measurement Scheme for an Advanced Lidar Atmospheric Profiling System", The Pennsylvania State University, Master's Thesis, 2002, 81 pages |