Overview:

These files contain the high sampling rate data from the ISFF towers during
TREX.  They were processed on 1 Mar 2008 using the calibration coefficients
known at that time.  Radiometer and soil sensor data have not been included
in these files since most users will only need the 5-minute averages
available separately.  The hot-film anemometers and aerosol sensor that
ISFF recorded were user sensors so their data will be distributed seperately.

Empty file:  Please note that the file c_20060228.tar.gz is empty.  No data
were collected at the central station on 28 February 2006.

Please note that there are several data processing steps that have not been
applied to these data:
- "tc" is acoustic temperature from the sonic anemometer that has a small
  dependence on humidity.  Humidity was generally low during TREX, so this
  difference is expected to be small.
- Simlarly, "kh2o" from the krypton hygrometer has a temperature dependence.
  We correct for this co-dependence in the statistics, but it is impossible
  to apply the corrections to the time series due to the (albeit relatively
  small) spatial separation between these sensors.
  (See: http://www.eol.ucar.edu/instrumentation/sounding/isfs/isff-support-center/how-tos/corrections-to-sensible-and-latent-heat-flux-measurements for more information on these corrections.)
- Large values of "kh2o" indicate that the optical signal is obscured
  (generally due to precipitation on the optics).
- ISFF sensors report only relative humidity.  Calculation of specific 
  humidity at 1 sample/s is left to the user (though it is calculated in
  the 5-minute average data set), so pressure data are included in this
  data set as well.

Format:
- File naming:
  - c/s/w indicating which ISFF site the data came from
    (central/south/west)
  - "_YYYYMMDD" for the date (beginning 00Z)
  - ".tar.gz" for the file format (zipped tar files)
- Each .tar.gz file contains up to 10 files.  Unpack with "tar -xzf xxx.tar ."
- There is one unpacked file for each sensor height on the tower at the site.
  They are named:
  - c/s/w_  indicating the ISFF site
  - 1/2/3/5/10/15/20/25/30m_ indicating the height above ground
    (files with "trh" have temperature/humidity data from all of the levels,
    plus surface pressure)
  - "_YYYYMMDD" for the date (beginning 00Z)
  - ".dat" for the file format (ASCII data)
- First line of each file has the variable names:
  - u/v/w/tc/diag/kh2o are from the sonic anemometer and krypton hygrometer
    reported at 60 samples/s.
    - westerly wind component (positive is wind to the East)
    - southerly wind component (positive is wind to the North)
      (see: http://www.eol.ucar.edu/instrumentation/sounding/isfs/isff-support-center/how-tos/wind-direction-quick-reference)
    - vertical wind component
    - acoustic temperature
    - diagnostic flag (0=good) for the sonic anemometer data
    - kh2o is the calibrated humidity (included at heights 5m and 30m).
      Note that there approximately every 6th sample has a duplicated value
      due to the sonic anemometer sampling faster than the hygrometer.
  - P/T/RH are pressure/temperature/relative humidity at 1 sample/s
  - All but "P" have a height qualifier: .1/2/3/5/10/15/20/25/30m
- Second line of each file are the units of measure for each variable.
- Following lines contain the data:
  - YYYY MM DD hh:mm:ss.ssss time tag of each sample in UTC
  - Data values for each variable.  "nan" are missing values.
  - The data have been synchronized to even times by chosing the sample
    nearest in time.
- Files are in "unix" format without "return"s.
- Files for 1,2,and 3m at central are empty until these anemometers were 
  connected to the primary data system on 28 March.

Documentation:
- http://www.eol.ucar.edu/rtf/projects/trex/isff/
  CHECK OUT the "Field Logbook" link in this document for details of sensor
  operation!

Contacts:
- Steve Oncley (oncley@ucar.edu)
- Gordon Maclean (maclean@ucar.edu)