Campbell Scientific Bowen Ratio Instrumentation - Manual (Page 27)

4-1
Section 4. Calculating Fluxes Using
SPLIT
SPLIT (LoggerNet software) can be used to calculate the fluxes from the Bowen ratio
measurements. This section describes these calculations on the data output from the
example datalogger program. It requires two passes with SPLIT to compute the fluxes.
The first pass operates on the raw data files generated by the datalogger. The definitions
of points in this data is given in Table 3-2 which is the Output from the sample program.
The output file from this first pass (RAWBOW.PRN) is defined in the parameter file
RAWBOW.PAR. The fluxes are then calculated by SPLIT with the parameter file
CALCBOW.PAR.
The example SPLIT parameter files: SERVICE.PAR, SHUTDOWN.PAR, RAWBOW.PAR,
and CALCBOW.PAR are on the Campbell Scientific, Inc. FTP site,
ftp://ftp.campbellsci.com/pub/outgoing/files/br_023a.exe.
4.1 Data Handling
Before calculating the surface fluxes, first Quality Control the raw data. Use
the SPLIT parameter files SERVICE.PAR and SHUTDOWN.PAR to
determine when the station was down for service or when it shut itself down
because of low battery voltage.
Next, combine the air temperature and vapor pressure gradients with net
radiation, soil heat flux, soil temperature, wind speed, and wind direction,
using the SPLIT parameter file RAWBOW.PAR.
This parameter file assumes that the data files from the datalogger were saved
on disk under the name BOWEN.DAT. It creates a file with the raw data
necessary to calculate fluxes RAWBOW.PRN.
Plot the data in RAWBOW.PRN, check the temperature and vapor pressure
gradient, soil heat flux and temperature, and net radiation for anomalous
readings. Check the wind speed and direction data to determine if the fetch
conditions are adequate.
4.2 Calculating Fluxes
Once the necessary data is in one file the fluxes can be calculated. The
constants and parameters necessary for calculating the fluxes are listed in
Table 4.2-1.
Most of the calculations in CALCBOW.PAR are explained in the overview in
Section 1. The method used to calculate the heat storage term and hence soil heat
flux at the surface is explained below.
The soil heat flux at the surface is calculated by adding the measured flux at a fixed
depth, d, to the energy stored in the layer above the heat flux plates. The specific