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6. TEMPERATURE EFFECT ON SOIL DIELECTRIC PERMITTIVITY-
DESCRIPTION OF LABORATORY SETUP AND APPLIED SOFTWARE
The purpose of the study, which uses the below described laboratory setup, is
to determine the temperature influence on the soil bulk dielectric permittivity, ε b ,
calculated from the measurement of the EM velocity of propagation in the soil
using TDR technique. The final effect is aimed at the adaptation of existing
physical models to account for the soil dielectric permittivity change caused by
the change of its temperature for mineral soils of variable texture and bulk
electrical conductivity. The developed model will help to interpret the influence
of selected soil physical parameters on its dielectric properties and will be used in
calibration of soil water content and conductivity reflectometric meters.
The soil bulk dielectric permittivity, ε b , change with temperature is not fully
explained yet (Or and Wraith [72]), but analysing equations (37) and (38) it can
be assumed that:
− ε b decreases with temperature increase because ε ' decreases following
the temperature effect of soil free water,
− ε b increases with temperature increase following the release of bound
−
water molecules,
ε b increases with temperature increase following temperature induced
increase of soil electrical conductivity, σ dc .
Reaching the described objective is requires the collection of experimental
data of the selected soil physical properties and developing the general physical
model of the temperature effect on soil dielectric permittivity. The tested material
consists of mineral soils of variable texture and specific surface area.
The complexity of applied experimental methods requires the application of
automatic measurement system. It consists of a central computer controlling the
sequence and time schedule of the measurement from individual sensors and the
temperature in the temperature chambers. The individual sensors are equipped
with intelligence in the form of microcontrollers that react on the commands from
the central unit and take over the control on the measurement process. The
measured data from the individual sensors of non-electrical quantities are
converted into digital form and sent back to the central unit for storage.
The collected data feed the general physical model of the form
ε = f ( θ, T,
ECa , ρ,
S ), where the arguments of the presented function are: soil
water content, temperature, apparent electrical conductivity, bulk density and
specific surface area, respectively.
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