1.2 Temperature Corrections
The Hydra Probe’s soil moisture and electrical conductivity measurements are temperature
corrected providing temperature independent data year round.
1.3 Calibrations
The Hydra Probe has four calibrations that provide excellent performance in most mineral soils
regardless of texture or organics. The calibrations are sand, silt, clay and loam. The loam soil
calibration is the default calibration and is suitable for Silt Loams, Loam, Clay Loam, Silty Clay
Loam, Sandy Clay Loam, Sandy Loam, and some medium textured clays.
1.4 Dielectric Permittivity
For research studies involving andisol pumas soil, wetland histasol soils or soil with extremely
low bulk densities, the uncorrected and the temperature corrected complex dielectric
permittivities are provided for custom calibrations.
1.5 Structural Components
There are three main structural components to the Hydra Probe. The marine grade stainless steel
tine assembly is the wave guide. The tine assembly is the four metal rods that extend out of the
base plate. Each tine is 45 mm long by 3 mm wide. The base plate is 25 mm in diameter.
Electromagnetic waves at a radio frequency are transmitted and received by the center tine. The
head or body of the probe contains the circuit boards, microprocessors, and all the other
electrical components. The outer casing is ABS and the internal electronics are permanently
potted with a rock-hard epoxy resin giving the probes a rugged construction. The cable has a
direct burial casing and contains the power, ground, and data wires that are all soldered to the
internal electronics.
1.6 Accuracy and Precision
The Hydra Probe provides accurate and precise measurements. Table 1.1 below shows the
accuracy. For a detailed explanation of accuracy and precision and on the statistical evaluation of
the Hydra Probe, see Appendix D.
Parameter
Accuracy/Precision
Temperature (C)
+/- 0.6 Degrees Celsius(From -30
o
to 36
o
C)
Soil Moisture wfv (m
3
m
-3
)
+/- 0.03 wfv (m
3
m
-3
) Accuracy
Soil Moisture wfv (m
3
m
-3
)
+/- 0.003 wfv (m
3
m
-3
) Precision
Electrical Conductivity (S/m)
TUC*
+/- 0.0014 S/m or +/- 1%
Electrical Conductivity (S/m)
TC**
+/- 0.0014 S/m or +/- 5%
Real/Imaginary Dielectric Constant
TUC*
+/- 0.5 or +/- 1%
Real/Imaginary Dielectric Constant
TC*
+/- 0.5 or +/- 5%
Table 1.1 Accuracy and Precision of the Hydra Probes’ Parameters
.
*TUC Temperature uncorrected full scale
**TC Temperature corrected from 0 to 35
o
C
7
