FILENAME:      shbclouds.readme.txt

DATASET TITLE:      SHEBA: ETL Radar-Lidar 10-min Cloud Physical Properties
                                   Version # 1, released on 11/30/01.
CONTACTS:                Matthew Shupe, matthew.shupe@noaa.gov, 303-497-6471.
               Janet Intrieri, janet.intrieri@noaa.gov, 303-497-6594
               Taneil Uttal, taneil.uttal@noaa.gov, 303-497-6409

SUMMARY:  Data set combines radar, lidar, and radiosonde measurements to give a
comprehensive view of cloud boundaries,  locations, and temperatures for the SHEBA annual
cycle.  Information includes: best estimated low cloud base and high cloud top, total cloud
thickness, total number of cloud layers, the presence and location of liquid in the atmospheric
column and temperatures at all relevant heights.

TIME PERIOD: 10/20/97 - 10/01/98.

INSTRUMENTS:
Millimeter Cloud Radar (MMCR) -    Moran et al. 1998 
Depolarization and Backscatter Unattended Lidar (DABUL) - Alvarez et al. 1998.
GPS/LORAN Atmospheric Sounding radiosonde system - Measuring temperature, humidity,
wind speed, and wind direction.  Soundings were taken twice daily for the SHEBA year with 4
launches daily during most of the months of April-July, 1998.

TECHNIQUES:
The combination of these data sets and any pertinent issues are discussed by Intrieri et al. 2002. 
Data set results are also discussed in that paper.  In short, cloud boundary information from both
radar and lidar were combined using various criteria to determine the most accurate cloud base
and top heights.  Temperatures for these levels were interpolated in time and space from
radiosondes.  Liquid water is identified in the atmospheric column using the depolarization
capabilities of DABUL.  

SAMPLING RESOLUTION: This data set is given on a 10-minute time scale.  Higher resolution
data is available from all instruments via other data sets available on this archive.
     
FILE FORMAT: NetCDF.

PARAMETERS (units):
See NetCDF header for all information on each parameter and the general data set.  Fields are:
dtime - Decimal day from 1/1/1997.  10-min time interval.
cldpresence - Cloud present in atmospheric column (boolean).
oper_r - MMCR operational (boolean).
oper_l - DABUL operational (boolean).
lb_b - Best estimated lowest cloud base (km AGL).
lb_bt - Temperature at "lb_b" (C).
lb_e - Lowest return height, either instrument (km AGL).
lb_et - Temperature at "lb_e" (C).
lb_ei - Instrument designating "lb_e".
lb_r - Lowest return height, radar (km AGL).
lb_l - Lowest return height, lidar (km AGL).
ht_e - Highest return height, either instrument (km AGL).
ht_et - Temperature at "ht_e" (C).
ht_ei - Instrument designating "ht_e".
ht_r - Highest return, radar (km AGL).
ht_l - Highest return, lidar (km AGL).
ct_r - Total cloud thickness, radar (km AGL).
ct_l - Total cloud thickness, lidar (km AGL).
nl_m - Maximum number of cloud layers, either instrument.
nl_i - Instrument designating "nl_m".
nl_r - Maximum number of cloud layers, radar.
nl_l - Maximum number of cloud layers, lidar.
liqpresent - Liquid layer present in column (boolean).
liqheight - Height of lowest liquid layer if present (km AGL).
liqtemp - Temperature at "liqheight" (C).
atten - Lidar attenuated (boolean).
precip - Precipitation present, based on these instruments (boolean).

KNOWN ERRORS: The lowest cloud base may be biased low during times when the DABUL
was not operational.  This low bias is due to the fact that the MMCR observes precipitation and
cloud, therefore the radar bases may actually be for the precipitation and not for the cloud.

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,
Proc. 10th Symp. on Meteor. Obs. and Instrumentation, 140-144. 

Moran, K.P., B.E. Martner, M.J. Post, R.A. Kropfli, D.C. Welsh, and K.B. Widener, 1998:  An
unattended cloud-profiling radar for use in climate research, Bull. Am. Meteorol. Soc., 79, 443-
455.
     
Intrieri, J.M., M.D. Shupe, T. Uttal, and B.J. McCarty, 2002b: Annual cycle of Arctic cloud
geometry and phase from radar and lidar at SHEBA, J. Geophys. Res., in press (SHEBA special
issue).