Explanation of SHEBA ETL/DABUL cloud product files submitted to Archive:


Files beginning with "CLD" are in ASCII format.  They contain cloud information 
derived from processing the DABUL lidar measurements.  The files span observations 
made from 1 November 1997 through 8 August 1998.  The lidar samples are obtained 
every 5 s but were averaged to 10 minutes for the cloud products presented here.  
All times are in UTC and all heights are in meters.

The CLD file names reflect the date and time for that file and in general there is 
one file per each day.  The files contain the following information in order of 
appearance;

year, month, day, hour, minute, second, number of layers, cloud base height, 
cloud top height, average intensity, average depol ratio, integrated depol ratio


General Background Information:

The Depolarization and Backscatter - Unattended Lidar (DABUL) is a pulsed 
laser-radar operating at 523 nm wavelength (Alvarez et al. 1998).  Range resolution 
is 30 m, and time resolution is 5 s. This lidar system uses a low energy laser with 
high repetition rates for good sensitivity while being completely eye-safe.

Data are collected in four channels according to receiver field of view and 
polarization detected: far parallel, far perpendicular, near parallel, and near 
perpendicular.  The far channel returns were used to determine the cloud layers due 
to it's high sensitivity.  Linear polarization is transmitted, and parallel and 
perpendicular refer to the polarization detected.  The depolarization ratios are 
obtained by taking the ratio of the perpendicular to parallel channels in either the 
near or far channels (Sassen 1991).

The cloud boundary determination was obtained by simply thresholding the intensity 
and depolarization values for cloud base and top height. After each cloud layer is 
determined (base and top heights) the average returned power and the depolarization 
values are assigned for as many layers as are detected.

Additional information or questions pertaining to the DABUL system should be 
directed to Dr. Raul Alvarez (ralvarez@etl.noaa.gov) and for information regarding 
the data fields or processing please contact Janet Intrieri 
(jintrieri@etl.noaa.gov). 


Additional information as well as examples of DABUL measurements can be found on
our web site:

 http://www2.etl.noaa.gov


References

        Alvarez, R.J., II, W.L. Eberhard, J.M. Intrieri, C.J. Grund, and S.P. 
Sandberg, 1998:  A depolarization and backscatter lidar for unattended operation in 
varied meteorological conditions. Proceedings, 10th Symposium on Meteor. Obs. and 
Instrumentation, 11-16 January, Phoenix, AZ,  American Meteorological Society, 
Boston, MA.

        Sassen, K., 1991: The polarization lidar technique for cloud research: A 
review and current assessment.   Bull. Amer. Meteor. Soc., 72, 1848-1866.