High Rate ISFS Data for SOAS

These data contain surface meteorology measurements of the Integrated Surface Flux System (ISFS) during the  Southern Oxidant and Aerosol Study (SOAS), at the Alabama Aquatic Biodiversity Center (AABC), during May, June and July of 2013.

For general information about the operations of the ISFS during SOAS see https://www.eol.ucar.edu/field_projects/soas.

The ISFS high rate dataset contains data from the 45 meter tower at the AABC site during during SOAS. 

The data are stored in NetCDF files. Information on the NetCDF file format and software is available at http://www.unidata.ucar.edu/software/netcdf/.  Information specfic to ISFS NetCDF files is available at https://www.eol.ucar.edu/content/isfs-netcdf-files.

NetCDF File Names

Each NetCDF file contains two hours of data. The file names are of the form "aabc_YYYYMMDD_HH.nc", where YYYYMMDD is the year, month and day in UTC, and HH is the UTC hour of the start of the data in the file.

NetCDF Variables

See the table at the bottom of this page for a listing of the variables in the file.

See the table at https://www.eol.ucar.edu/content/soas-isfs-page for information on the sensors that were deployed.

Time Representation

The base_time variable contains one value, the time of the start of the file, as a number of POSIX (non-leap) seconds since 1970 Jan 1, 00:00 UTC.

Values for each time-varying measurement will be found in the NetCDF files, as a variable with a time dimension.

Before being written to the NetCDF files, the raw, asynchronous samples are re-sampled to an evenly spaced time sequence, using a simple method of matching the raw sample nearest-in-time to the evenly-spaced times. No interpolation or averaging is done.

Variables of three time resolutions are stored in the files. State parameters such as temperature and humidity were sampled at 1/sec. These variables will have a time dimension of 7200,  the number of samples in two hours.  Data from sonic anemometers, fast water vapor and CO₂ gas analyzers were sampled at 20/sec. These variables will have an additional sample dimension of 20 in addition to the time dimension.  Pressure data was sampled a approximately 14.85 /sec. These are stored with a sample dimension of 15.

The time variable contains the time to be associated with each 1 Hz sample, in units of seconds since base_time.  Each time value is the middle of the second.

For  variables with a sample dimension of 20, the timetags for the 20 samples of the second are evenly spaced around the corresponding time. The time-tag for a sample from a variable with time index i, sample index j, is:

t_i,j = base_time + time_i - 0.5 + (1/20) x (1/2 + j)

i is the time index

j is the sample index, ranging from 0 to 19 (sample dimension minus one)

In a similar manner, the time-tags of the 15 Hz pressure data are:

t_i,j = base_time + time_i - 0.5 + (1/15) x (1/2 + j)

j is the sample index, ranging from 0 to 14

Dimensions

The NetCDF dimensions in each file are:

Short Name Attributes

Each measured variable will have a short_name NetCDF attribute. The field before the first period in the short_name is a generic variable name, such as T for temperature, or u for the U component of the wind.

Heights

The height in meters above ground of the measurement, if appropriate, will be indicated in a second field after a period in the short_name, for example RH.26m, or u.38m.

Variable Names

The actual NetCDF variable names will have underscores, '_', in place of periods and single quotes.  Therefore a variable with a short_name attribute of co2.38m will have a NetCDF variable name of co2_38m.

Units and Long Names

Each variable will have NetCDF attributes containing the units of the measurement, and a long name giving more information on the measurement.

Missing Data

The missing data value is 1x10^37.  A missing value indicates either that the sensor was not reporting at the given time, or it was detemined that the data value did not meet QC criteria during post-project analysis.

Table of NetCDF Variables