Here is some information regarding the ceilometer data recorded on the
R/V Ron Brown during NAURU99.  The user has the option of getting the raw
15-s time resolution data and/or statistics of the 15-s data.  The
15-s data and statistics are contained in ASCII-based files.  Daily and 
experiment summary plots of the statistics are available in postscript.  All
files are compressed with Winzip and stored in the following archive files:

rawbase_data.zip        15-s raw sky designation and cloud base data
stat_data.zip           Daily files of hourly summary statistics
basedist_data.zip       Daily files of cloud base frequency distributions
stat_plots.zip          Postsript images of daily summary statistics
experiment_summary.zip  Statistical summary files
realtime_displays.zip   Data acquisition program display images

The files mentioned above are available through ftp.

ftp etl.noaa.gov 
username> anonymous
password> your email
cd /pub/et7/users/abw/nauru99/ceilom
binary (transfer of *.zip files)

The file names in the rawbase_data.zip archive are of the form 
MM_DD_YY.cld, where
	MM = month (i.e., 01 = Jan.)
	DD = day of the month
	YY = year (i.e., 99 = 1999).
In these files there are 7 columns of data:
	sky designation
		0 = clear
		1 = single cloud layer detected
		2 = two cloud layers detected
		3 = three cloud layers detected
		4 = totally obscured conditions
		5 = partially obscured conditions
	height of lowest detected cloud base in meters
	height of second detected cloud base in meters
	height of third detected cloud base in meters
	GMT hour
	GMT minute
	GTM second

	"Totally obscured" conditions usually occur in fog or precipitation. 
"Partially obscured" conditions occur when the ceilometer algorithm detects a 
signal that does not fit the pattern of a "hard" cloud boundary.  When the 
sky designation is totally obscured, the value reported in the second column 
is a calculation of vertical visibility.  In these cases, the third column 
reports the maximum height that a signal was detected.  The totally obscured 
data were included in the computation of cloud fraction statistics, but not of 
cloud base statistics.  The partially obscured data were thrown out before 
any statistics were computed.

The 15-s ceilometer data were used to generate hourly cloud base and
cloud fraction statistics.  The data are contained in files sMMDDYY.dat in the 
stat_data.zip archive.  These daily files contain 16 columns:
 
	month
	day
	Julian day
	GMT (middle of hour)
	# of "total" 15-s data points
	# of "clear" data points
	# of "single cloud base" data points
	# of "multiple cloud base" data points
	# of "totally obscured" data points
	# of "partially obscured" data points
	clear fraction
	cloud fraction without including totally obscured points
    * cloud fraction including totally obscured points
	20th percentile cloud base (m)
	50th percentile (median) cloud base (m)
	80th percentile cloud base (m)
 
The file expstat.dat in the experiment_summary.zip archive has the same 
format except there is a header line and there is an extra column after 
the one above labeled with (*) that gives the fraction of partially obscured 
data points (i.e., the fraction of data thrown out prior to computing the 
statistics).

The file names of the daily cloud base frequency distribution files in the
basedist_data.zip archive are of the form dMMDDYY.dat.  These daily files 
contain three columns:
 
	cloud base (km) -- center of 100-m interval
	number of occurrences within 100-m range
	frequency/100 of occurrence
 
The file expbdst.dat in the experiment_summary.zip archive has the same 
format.

The cMMDDYY.ps files in the stat_plots.zip arcive are postscipt images
containing summary graphs for the daily ceilometer data.

The expdiurn.dat file in the experiment_summary.zip archive contains diurnal
averages of cloud fraction and cloud base.  This file contains three columns:
 
	Time (center of GMT hour)
	cloud fraction
	cloud base (km)

The expfdst.dat file in the experiment_summary.zip archive contains a number
and frequency distribution of hourly cloud fractions.  This file contains
three columns:

	cloud fraction (center of 1/10 range)
	number of hourly occurrences 
	frequency/100 of occurrence

The file expstat.ps in the experiment_summary.zip archive is a postscript 
image containing experimental summary graphs.

The MM_DD_YY.am or .pm files in the realtime_displays.zip archive 
contain the data acquisition program screen display stored at the end of 
each 12-hour period.  These files may be imported into a word processor 
(e.g., WordPerfct v9) for viewing.
	
The maximum range of the ceilometer is 7620 m, and the resolution in the
profiles is 15 m (50 ft).  Other details on operation of the Vaisala CT25K 
are given by White (NOAA Tech Memo. ERL ETL-281, NOAA Environmental 
Technology Laboratory, 325 Broadway, Boulder, CO 80303, 1997).  A comparison 
of ceilometer data collected in four different climate regimes (FIRE/SCOPE, 
ASTEX, TIWE, COARE) is given by White et al. (JAS, 52, 2827-2838). A
comparison of ceilometer data recorded on Manus Island and onboard the R/V 
Discoverer during the 1996 Combined Sensor Program is included in Post et al. 
(BAM, 78, 2797-2815).

Any questions regarding these data should be directed to
Allen White
awhite@etl.noaa.gov
(303) 497-5155