Appendix D - Statistics
All measurements, no matter how careful and scientific, are subject to some uncertainties.
Statistics is the branch of mathematics that can quantify uncertainties. The Hydra Probe’s design
and signal processing reduces error to a magnitude that has little impact on hydrological
measurements such as permanent wilting point, field capacity and saturation.
Parameter
Accuracy/Precision
+/- 0.6 Degrees Celsius(From -10
o
to 36
o
C)
Temperature (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
The Hydra Probe offers better precision and accuracy than TDR and other FDR type soil probes
because:
1)
the signal response is ratiometric maximizing reproducibility,
2)
the frequency of 50 MHz provides enough energy to achieve the molecular polarization
of water while maintaining a quantifiable imaginary dielectric constant,
3)
the values are temperature corrected, and
4)
the calibration curves are solute independent in most soil environments and have high R
2
values.
The Hydra Probe’s precision was calculated from the standard deviation. The accuracy of the
soil moisture measurements were calculated from the deviation about the calibration curve. In
most cases, the R
2
value for soil moisture is 0.97 to 0.99. The accuracy of the soil electrical
conductivity was calculated from the standard deviation of measurements taken in conductivity
standards.
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