SGP/ARSCL/C1 - ARSCL Cloud Bases and Low-level reflectivities

Prior to February 4, 2000, the ARSCL data set incorporated data from the
Beaufort Laser Ceilometer as one of its inputs.  Because of the BLC's
high spatial resolution, this data was often chosen by ARSCL as the
"CloudBaseBestEstimate" for boundary layer clouds. It was subsequently
determined that the BLC cloud base was biased, with the BLC reporting
cloud base heights that are 122 meters too high.

The bias error will be corrected when the entire ARSCL data set is
reprocessed as part of release_4.  (The release version number is included
the the netCDF global comments).   This reprocessing will also include a
small correction the the MMCR near-field reflectivities.  This correction
is less than 1 dB except for hydrometers within 200 meters of the surface.

Thanks to Roger Marchand for helping bracket this problem.

It is recommended that ARSCL users examine the variable "CloudBaseCeilometerStd" 
in the "sgparscl1clothC1.c1" files. When "CloudBaseBestEstimate" == 
"CloudBaseCeilometerStd", the BLC was used as the cloud base best estimate,
and a value 122 meters less than the given value should be used as the actual
cloud base.

• BLC/VCEIL Standard Algorithm Cloud Base Height(CloudBaseCeilometerStd)
• LASER Cloud Base Height Best Estimate(CloudBaseBestEstimate)
• MMCR Best Estimate of Hydrometeor Reflectivity(ReflectivityBestEstimate)
• Reflectivity(Reflectivity)
• BLC/VCEIL Clothiaux et al. Algorithm Cloud Base Height(CloudBaseCeilometerCloth)

• BLC/VCEIL Standard Algorithm Cloud Base Height(CloudBaseCeilometerStd)
• BLC/VCEIL Clothiaux et al. Algorithm Cloud Base Height(CloudBaseCeilometerCloth)

• LASER Cloud Base Height Best Estimate(CloudBaseBestEstimate)