THE LANGLEY 8" LIDAR SYSTEM AT PARSONS, KANSAS ORIGINAL VERSION: 11/19/91 The lidar deployed by Langley Research Center(LaRC) at a field site (37.18"N, 95.07"W, 865 ft above MSL) near Parsons, Kansas for the FIRE IFO during November 13 to December 6, 1991 was the LaRC 8" Lidar System housed in a recreational vehicle situated at the site in Parsons. This lidar system is comprised of a frequency doubled Nd:YAG laser serving as the lidar transmitter and an 8" Cassagrain depolarization sensitive receiver system attached to a 386 based data acquisation system . The table below presents the operating parameters of this lidar system as it was configured and used for the FIRE Kansas IFO. TRANSMITTER Wavelength 532 nm Pulse Energy 150 mJ Pulse Rate 10 Hz Pulse Width 6 ns Beam Divergence 0.6 mrad Beam Diameter 6 mm RECEIVER Telescope Diameter 20 cm Field of View 2 mrad Filter Bandwidth 1 nm, 50% transmittance, centered at 532 nm Detector, PMT EMI 9658 Quantum Efficiency 15% Calibration Zero order half-wave plate mounted on rotatable assembly used for depolarization calibration DATA ACQUISATION AND ANALYSIS SYSTEM Computer 386 system, 20 Mz A/D Resolution 12 bits Altitude Points 4096 Altitude Limits 0 to 60 km, 2 to 15 km normal data range Altitude Resolution 30 m, amplifier bandwidth usually degrades this resolution Storage Media Optical Disk, 400 Mb per disk Data Analysis 486 system, 33 Mz Graphics Plotter 286 system, 12 Mz and inkjet printer Lidar Record Elementary unit of recorded data consists of hardware average of 150 lidar pulse responses(15 second average) Data acquisation commenced at 6:00 am on Wednesday, November 13, 1991 and continued intermittently until 11:29 am Friday, December 6, 1991. Approximately 700 Mb of raw data were collected at the field site during a cumulative 143 hours of operation. As mentioned above, the basic unit of data collection were 150 lidar pulse responses averaged over 15 second intervals. The operational time periods of the LaRC 8" Lidar System at Parsons are presented in the last image in the file b_ci2_l8_lidar_yymmdd.hdf. The "other obs" refers to lidar operation occurring during times where no cirrus were were detected. During these times either the sky was clear or the detected low level clouds were obscuring overlying cirrus. The color lidar graphs provided by the Langley Research Center's Aerosol Research Branch(ARB) FIRE Lidar researchers are presented in the browse images labeled b_ci2_l8_lidar_yymmdd.hdf. Each browse image file includes attenuated Scattering and Depolarization ratio images for each day, where yy is the year the data were collected, mm is the month the data were collected and dd is the day of the month the data were collected. In concurrence with the FIRE lidar graphics guidelines, the total time elapsed in each color plot is 6 hours and the plots are started at 0, 6, 12, and 18 hours GMT. The information presented in the color catalog graphs consists of the "attenuated backscatter" ratio represented by different colors as a function of altitude and time(GMT)." A short description of the term "attenuated backscatter" ratio follows. If atmospheric and cloud aerosol scattering are to be explicitly considered, the signal S(r) received by a lidar system contains energy from two scattering sources and is given by the first equation in the last image file of b_ci2_l8_lidar_yymmdd.hdf. In the equation, D is a constant for any one lidar record, beta represents the volume backscatter coefficient, sigma is the extinction coefficient, r is the range, and the lower limit of integration is the the cloud base altitude. For each lidar record we experimentally determine a value for D. This constant is determined by fitting an atmospheric model or a rawindsonde sounding to a suitable part of the lidar return situated below the cloud. The altitude where the fit is performed is the "normalization" altitude. We then divide the actual value of the lidar signal at every altitude by the value of the lidar signal from a cloudless sky and we call the result the attenuated scattering ratio. The cloudless sky value is determined by extrapolating the signal fit from the normalization altitude to other, higher altitudes. Atmospheric extinction is included in the calculation. The second equation in the last image file of b_ci2_l8_lidar_yymmdd.hdf presents the expression representing the attenuated scattering ratio. We expect to update this information file as more lidar data are added to the data base. J. M. Alvarez Langley Research Center Mail Stop 417 Hampton, VA 23665 Phone (804) 864-2677 Fax (804) 864-7711