30 Second ISFS Data for METCRAXII

These data contain surface meteorology measurements of the Integrated Surface Flux System (ISFS) during the second Meteor Crater Experiment (METCRAXII), at the Barringer Meteor Crater, Arizona, during October of 2013.

For general information about the operations of the ISFS during METCRAXII see https://www.eol.ucar.edu/content/isfs-metcraxii.

The ISFS 30 second datasets contain first moments of many variables measured by the NCAR ISFS.

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

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.

30 Second Datasets and Download URLs

Two 30 second datasetsare available. They each contain QC'd 30 second means of a selection of sampled variables, and some derived variables.

netcdf_qc_geo_tiltcor_30s, http://data.eol.ucar.edu/codiac/dss/id=386.002: All wind vectors have been rotated to geographic coordinates (+U is wind to the east, +V is wind to the north), and 3D wind vectrors are corrected for tilt of the anemometer relative to a plane of mean flow (see #SonicTiltCorrection).
netcdf_qc_geo_notiltcor_30s, http://data.eol.ucar.edu/codiac/dss/id=386.004: Same variables as in netcdf_qc_geo_tiltcor_30s, but the 3D winds have not been corrected for sonic tilt.

Quality Control, Corrections, Derivations

The QC procedure consists removing the high rate data (i.e. replacing it with the missing data value) during periods where it is determined that the data does not meet QC criteria. This is done before the statistics were computed.

See Notes On Quality Control for details. Here is a quick summary:

The online field logbook logbook has detailed information about sensor issues that were noted in the field.

u, v, w, tc from the CSAT3 sonic anemometers have been removed when ldiag, from the the CSAT3 diagnostic bits, is non-zero.
P.nne.flr, P.sw.flr, P.w.flr data were removed during periods of sensor problems, as determined by anomalous data.
T, RH values removed when the aspiration fan current, Ifan, of the ventilated hygrothermometer was out of normal range and during periods of other sensor problems.
Radiometer Rpile and Rsw values removed when Wetness indicates the presense of liquid water, when notes in the field log indicated the optics were dirty, when the radiometers were being cleaned, and for periods of known wiring problems.

The following corrections and derivations have been applied to both datasets

All horizontal wind components, U and V from 2D anemometers, and u and v from fast 3D anemometers, have been rotated to geographic coordinates, where +U is wind to the east, +V is wind to the north. These rotations are based on compass measurements of the anemometer orientations.
long wave radiation, Rlw, has been derived from the pyrgeometer thermopile measurement (Rpile) and case temperature (Tcase) measurments, using the Albrecht-Cox equation.

NetCDF File Names

Each NetCDF file contains one day of data, from 00:00 to 24:00 UTC. The file names are of the form "isfs30s_YYYYMMDD.nc", where YYYYMMDD is the year, month and day in UTC.

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. The time dimension will be 2880 for a complete file, the number of 30 second periods in a day.

The time variable contains the time to be associated with each sample, in units of seconds since base_time, or 00:00 UTC of the day. Each time value is the middle of the averaging period, and will have values of 15 (00:00:15 UTC), 45 (00:00:45), etc, up to 86385 (23:59:45 UTC).

Dimensions

The NetCDF dimensions in each file are:

Dimension Name	Size	Description
time	2880	number of 30 second periods in a day
site	5	index for the five ISFS sites at METCRAXII: flr, rim, base, near, far

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, Rsw for short wave radiation, 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.30m.rim.

Tower Sites

The last period-separated field in the short_name attribute is the site name, "flr" (crater floor), "rim", "base" (next ISFS base trailer), "near" and "far".

NetCDF 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 U.3m.near will have a NetCDF variable name of U_3m_near.

Units and Long Names

Variables have a NetCDF attribute specifying the units of the measurement. Many variables have a long_name attribute giving more information on the measurement.

Missing Data

The missing data value is 10³⁷. 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.

Sonic Tilt Correction

The 3D sonic anemometers were installed as level as was possible, but not perfectly "bubble" level.

The netcdf_qc_geo_tiltcor dataset contains 3D wind vectors and second moments which have been rotated to a coordinate system where the mean W component is zero, as described in "/content/sonic-tilt-corrections."