Instruments:usl

From CedarWiki
Jump to: navigation, search

USU Rayleigh Lidar

Contents


Contact Persons

Web Sites

Acknowledgments

The Utah State University Rayleigh lidar is operated by the Utah State University with support from the National Science Foundation.

Instrument/Model Description

The Utah State University (USU) Rayleigh lidar at the Atmospheric Lidar Observatory (ALO) is run by the Center for Atmospheric and Space Sciences (CASS). It is located at Logan, Utah at (41.74N, 111.81W) on the roof of the Science and Engineering Research (SER) building on campus. The height is 1466 m using the WGS84 geoid to represent the earth. The lidar is operated in the vertical direction and can obtain data on all non-heavy cloud nights. (Thin cirrus clouds are OK.) An operator is present to operate the system and for aircraft safety. The lidar started operations in August 1993, with relatively regular operations up to the present except between April 1997 and May 1998 when the lidar was not operating.

The lidar operates at a wavelength of 532 nm up to about 500 km, but collects meaningful data only between about 45 and 100 km. The height resolution of the data is originally 37.5 m using 3600 shots (30 per sec) over 2 minutes. However, averaging is done over 81 range gates (81*37.5m = 3.0375 km) with a sliding average reported every 112.5 m (3 range gates). The number of 2-min integrations is reported as Code 415. Hourly averages of 29 or less 2 minute intervals are calculated, where cloudy or otherwise unusable periods have been eliminated in the hourly average (kindat=17002). Nightly average profiles are also computed (kindat=17001).

The data is affected by several factors. We assume Rayleigh scattering off molecules, but if volcanic aerosols are present in the lower part, or noctilucent clouds with ice crystals are present in the upper altitudes, then the scattering is Mie scattering and the Rayleigh assumption breaks down. Mie scattering in the data will tend to lower the derived temperatures. Other factors are saturation of the photomultiplier tube by signal at 40 km, so the normalization altitude is chosen between 45-50 km, and the temperature data is good down to at least 45 km. Saturation effects raise the derived temperature. Finally the background count is measured between about 120 and 150 km, and is subtracted from the measurements below. The photocounts are integrated downwards starting at the height at which the signal is 16 times the standard deviation. Uncertainties in the background removal can affect temperatures above 80 km, but should be negligible below 75 km.

References for the instrument and data processing procedures

Beissner, K.C., Studies of mid-latitude mesospheric temperature variability and its relationship to gravity waves, tides, and planetary waves, Ph.D. thesis, Utah State University, Logan, UT, 1997.
Hauchecorne, A., and M.L. Chanin, Density and temperature profiles obtained by lidar between 35 and 70 km, Geophys. Res. Lett., 7, 565-568, 1980.
Hauchecorne, A., M.L. Chanin, P. Keckhut, and D. Nedeljkovic, LIDAR monitoring of the temperature in the middle and lower atmosphere, Appl. Phys. B, 55, 29-34, 1992.
Keckhut, P., A. Hauchecorne, and M.-L. Chanin, A Critical Review of the Database Acquired for the Long-Term Surveillance of the Middle Atmosphere by the French Rayleigh Lidars, J. Atm. Oceanic Tech., 10, 850-867, 1993.
Wickwar, V.B., K.C. Beissner, T.D. Wilkerson, S.C. Collins, J.M. Maloney, J.W. Meriwether, and X. Gao, Climatology of mesospheric temperature profiles observed with the Consortium Rayleigh-scatter lidar at Logan, Utah, in Advances in Atmospheric Remote Sensing with Lidar, edited by A. Ansmann, R. Neuber, P. Rairoux, and U. Wandinger, pp. 557-560, Springer Verlag, Berlin, 1997.

Summary Plots for USU Rayleigh Lidar


-Revised 12 Aug 2002 by Barbara Emery