NEC-LIST: SRI OWL Kit Accuracy

All:

It is really difficult to give a good general answer on how accurate
the various techniques are for measuring in-situ values of surface
soil conductivity and relative permittivity, since so many variables
come into play. One thing is sure, the values are good at the time
that they are measured, but if the soil mositure changes, then both
"ground constants" change also. I have been convinced for a long time
that in- situ data are superior to lab sample data for the kind of
inputs we need for NEC and related types of models. The lab samples
can exhibit much lower values, even when carefully done, due to
evaporation of soil moisture between the time the sample is acquired
and when it is measured in the lab. Even if the soil is immediately
placed in a hermetically sealed container, the loosening of the soil
during the sample gathering process causes the sample to be somewhat
less compacted than in-situ. These added air molecules in the soil
decrease both the conductivity and the relative permittivity, and also
make it easier for the soil moisture to escape.

All for now. I am doing a short note for Perry Wheless for his CEMist
column in the ACES Newsletter on the variation of soil conductivity
and relative permittivity vs frequency and soil moisture content (in
%, by volume). Watch for it in the issue after the one just going to
press.

George
Received on Thu Jun 18 1998 - 10:03:19 EDT