README file for SYNoptic Local Time (SYN_LT) CAVE data files.

Summary:
--------

CAVE surface observations consist of a host of radiometric, meteorological, 
and aerosol observations taken at a number of sites around the globe. Many 
organizations and people have generously made their data available for 
dissemination through this web site.  That data, generally arrives at 
1 minute temporal resolution and for our purposes is averaged to 15 minute 
means. The data is rewritten as binary files, each file contains a header 
and all available data for a single site for a single month. These are then 
released using the http tool along with programs to read the files. See:

   http://www-cave.larc.nasa.gov/cave/pages/sam.html

for a complete description of the files; a complete lists of available 
months for each surface site;  an on-line plotting tool that prints summary 
tables of all variables available at a given site and plots desired variables.

These "synoptic" files have taken the 15 minute average data from the
SAM files and averaged the data to longer time scales. Included in these
files are averages of all variables to:

    1 Hourly
    3 Hourly
   24 Hourly (Daily mean)
   Monthly Mean*

Each variable has 3 associated records.

  1: Temporal average (mean)
  2: Standard deviation over time period.
  3: Count of values used to calculate mean and standard deviation.
   (The count for the monthly mean is the percentage of total
    possible hourly values used in the calculations. This is done
    to give a better idea of total data available for the calculation.)

The Local Time (LT) suffix indicates that the first time step of each
record is for Day 1, 00:00 Local Time. Similiar files, but averaged in 
GMT are also available. These files have the suffix ".UT" All averages 
are to the middle of a respective time period. eg. The 1 hour average 
for hour 0 is an average +/-30 minutes of 0:30

(--------------------------------------------------------------------------
(* Monthly Mean calculation: 
(
(  Gaps of up to 3 hours in the 15 minute data are interpolated to fill 
(      missing observations.
(  A monthly mean diurnal cycle is calculated for all radiation variables.
(  The monthly mean is simply the average of the monthly mean diurnal cycle. 
(--------------------------------------------------------------------------

File Format:
------------

Data are direct access, 8-bit binary, of record length 4096 bytes.
They are written using fortran 90 code on an Unix-SGI (i.e. Big-Endian)
Each file consists of a Header record that contains information regarding 
the surface site and a list of variables contained in each file. The 
remainder of a file contains three records (mean, standard deviation, count)
for each available variable where each 3 record group is one month's worth 
of data for that variable. For the synoptic files each record has the hourly,
3 hourly, daily and monthly mean packed into each record. The read routine 
unpacks the time series into separate arrays.

Basic Data Set:
---------------

Each file contains a basic list of 22 variables (not all of which 
are necessarily available.) 

Header

 Character (Len=64) :: Site_ID              !   64 bytes   64 
 Character (Len=4)  :: year                 !    4 bytes   68
 Character (Len=4)  :: mon                  !    4 bytes   72
 Real	 :: lat                             !    4 bytes   76
 Real	 :: lon                             !    4 bytes   80
 Real	 :: elev                            !    4 bytes   84
 Real	 :: extras                          !    4 bytes   88
 Character (Len=32), Dimension(50) :: label ! 1600 bytes 1688
 Character (Len=2408) :: padding            ! 2408 bytes 4096(=1024*4)
                                                                / \
                                                       744 + 248 + 31 + 1
                                                        /     /     \    \
                                                  Hourly  3-Hourly Daily Monthly
Data                                                                      Mean

( 1) = 'Cos(Sol Zen Ang)   (-----)
( 2) = 'LW Flux DN	   (W/m*m)
( 3) = 'LW Flux UP	   (W/m*m)
( 4) = 'SW Global DN	   (W/m*m)
( 5) = 'SW Global UP	   (W/m*m)
( 6) = 'SW Direct Normal   (W/m*m)
( 7) = 'SW Dif DN UnAdj    (W/m*m)
( 8) = 'Total SW Dn,Dir+Dif(W/m*m)
( 9) = 'Temp 10m	   (Deg C)
(10) = 'Sfc Pressure	   (   mb)
(11) = 'Sfc Wind Speed     (  m/s)
(12) = 'Sfc Wind Dir	   (+degN)
(13) = 'Sfc Rel Humidity   (	%)
(14) = 'Cloud Fract (SWFA) (  0-1)
(15) = 'Aer OD-1 nnnn nm   (-----)
(16) = 'Aer OD-2 nnnn nm   (-----)
(17) = 'Aer OD-3 nnnn nm   (-----)
(18) = 'Aer OD-4 nnnn nm   (-----)
(19) = 'Aer OD-5 nnnn nm   (-----)
(20) = 'Aer OD-6 nnnn nm   (-----)
(21) = 'Aer OD-7 nnnn nm   (-----)
(22) = 'Aer PW  	   (   cm)

Beyond this list files may contain extra data. The number of extra
variables (if any) is given in the header record by the variable "nextra".

For example all SURFRAD sites have UVB and PAR radiation along
with their basic suite of instrumentation.