5TE Operator’s Manual
4. Calibration
11
4. Calibration
Dielectric Permittivity
Each 5TE sensor has been calibrated to measure dielectric
permittivity (
ε
a
) accurately in the range of 1 (air) to 80 (water).
The unprocessed raw values reported by the 5TE have units
of
ε
a
*50.
Mineral Soil Calibration
Numerous researchers have studied the relationship between
dielectric permittivity and volumetric water content (VWC) in
soil. As a result, the soil science literature is littered with vari-
ous transfer equations used to predict VWC from measured
dielectric permittivity. You are free to use any of these various
transfer equations to convert raw dielectric permittivity data
from the 5TE into VWC. In Decagon’s ProCheck reader and
DataTrac and ECH
2
O Utility software packages, if the mineral
soil calibration option is chosen, raw dielectric permittivity
values from are converted to VWC using the well known
Topp equation (Topp et al, 1980):
VWC=4.3X10
-6
ε
a
3
- 5.5X10
-4
ε
a
2
+2.92X10
-2
ε
a
- 5.3X10
-2
Our tests have shown that a properly installed 5TE sensor
installed in a normal mineral soil with saturation extract elec-
trical conductivity <10 dS/m, the Topp equation will result in
measurements within ±3% VWC of the actual soil VWC. If
you require more accurate VWC than ±3% or are working in a
