OPEC Eddy Correlation System
J. H. Blanford and L. W. Gay 1992, Test of a Robust Eddy Correlation System for Sensible Heat flux , Theor. Appl. Climatol. 46.53-60
Eddy correlation equipment can be used to measure the
evapotranspiration rate from natural and crop land. The eddy correlation equipment
measures sensible heat flux and Et is calculated from the energy balance equation. where
Rn+LE +H+ Gsoil+ Gcanopy = 0. The equipment is a simple one-propeller eddy correlation
system (OPEC) described below. The thermal
storage component in the canopy (Gcanopy) can be calculated from air temperature and
an estimate of the biomass. The system uses a Campbell cr10x data logger and the program
for the data logger cr10x data logger calculates the LE. The output
of the program has to have the LE values corrected for stability and thermal
storage if this is significant. The stability correction is applied to the program
output subsequent to the measurements. The period means of sensible heat (30-minutes in
this OPEC program) must be multiplied by 1.4 for advective downward fluxes to the canopy
(negative output) and by 1.1for convective upward fluxes into the atmosphere (positive
output). The basis for this correction is discussed with respect to theoretical and
practical considerations by Blanford and Gay (1992). Net radiation values have a constant
in the program related to the net radiometer and this also must be corrected for wind
conditions as specified by the manufacture.
Step by step instructions and complete materials list for the construction of a complete OPEC system using a tripod to mount the system 18 ft above the ground.
Maintainance: How to maintain the opec equipment.
Data Analysis: Example of data from data logger and analysis