Readme file for the NOAA/ARL/SRRB Hemispheric Sky Imager Cloud 
Fraction retrievals during the CASES 1997 Experiment.

The cloud fraction files are in ASCII format, with the extension
"cfp". File names are in YYYYMMDD format (see below). Time is given 
in both Local Standard Time (LST) and GMT for convenience. However, 
due to operational scheduling concerns, and for ease of operation on 
various field projects in differing locations, the system is run 
using LST. Thus the DATE listed in the files is in LST, not GMT.

Note that these cloud fractions are HEMISPHERIC cloud fractions, i.e.
they represent the sky cover as "seen" by a pyranometer. This is NOT 
the same view as that from satellite, but resembles that of an 
observer on the surface. The values are determined from "pixel 
counting" as each image is processed.

The All-Sky Camera was located at Site 7 (37.4442 N, 96.9995 W).
Reference: CASES-97 Ops plan, p. 19, Table 4 in LeMone, Margaret A., and 
Coauthors, 2000: Land.Atmosphere Interaction Research, Early Results, 
and Opportunities in the Walnut River Watershed in Southeast Kansas: 
CASES and ABLE. Bull. Amer. Meteor. Soc., 81, 757.779, 
doi: http://dx.doi.org/10.1175/1520-0477(2000)081<0757:LIRERA>2.3.CO;2 
http://journals.ametsoc.org/doi/abs/10.1175/1520-0477%282000%29081%3C0757%3ALIRERA%3E2.3.CO%3B2.


File Header Key:

date - date in LST, YYMMDD where YY is the last 2 digits of the year,
	MM is the month, DD is the day.
Ltim - Local Standard Time, based on longitude (NOT political boundaries).
Ztim - GMT.
adfl - processing flags for QC, ignore.
CF - Hemispheric fractional sky cover.
TCF - thin CF, difference between this and CF gives opaque CF.
ZCF - CF for 20-25 degree FOV centered at zenith.
SCF - CF for 40 pixel radius around the sun in the image. Thus FOV 
	for this changes as solar position in image changes. Used
	in processing.
E2A - Hemispheric cloud edge-to-area ratio. If retrieved CF is less
	than 0.5, this is set to zero. For CASES97, since the HSI
	mirror was not cleaned regularly by the onsite personnel, this
	value must be considered in error due to accumulated dirt.
CosZ - cosine of solar zenith angle at time of image.
Azim - solar azimuth angle, adjusted to E=0, at time of image.
Decl - solar declination angle at end of day.


For more information or comments, contact:
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Dr. Charles N. Long
Penn State University
Dept. of Meteorology
503 Walker Bldg.
University Park, PA  16802

e-mail:  long@essc.psu.edu
Phone: (814) 863-9400
FAX:  (814) 865-3663
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