Delta-T HH2, User Manual

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About Soil Parameters a0 & a1
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These soil parameters are a convenient and efficient way of describing the calibration
curves for different soil types without the overhead of a unique linearisation table for
every different soil.
It is also a lot easier experimentally to derive an a0 and a1 for your soil than to
measure the complete calibration table.
For optimum accuracy you should obtain these parameters, a0 and a1,
experimentally for your soil as described in your sensor user manual. Then enter
these via the Soil Set-Up menu in the HH2.
Using Default values of a0 & a1
Alternatively you can choose the Mineral or Organic option in the Soil Types sub
menu. You may lose some absolute accuracy (up to ~ 4% volumetric water content)
but it is easier. Mineral and Organic soil coefficients are permanently installed in the
HH2 as follows:
a0 a1
Mineral soils 1.6 8.4
Organic soils 1.3 7.7
These values are derived from the paper by Roth et al 1992 – see below.
The other references below trace the validation of the method.
References
1. Topp, G.C., Davis, J.L. and Annan, A.P. 1980
Electromagnetic determination of soil water.
Water Resour. Res. 16(3) 574-582
2. Roth, C.H., Malicki, M.A. and Plagge, R 1992
Empirical evaluation of the relationship between soil dielectric constant and
volumetric water content as the basis for calibrating soil moisture measurements.
Journal of Soil Sci. 43, 1-13
3. Whalley, W.R. 1993
Considerations on the use of time-domain reflectometry (TDR) for measuring soil
moisture content.
Journal of Soil Sci. 44, 1-9
4. White, I., Knight, J.H., Zegelin, S.J. and Topp, G. C. 1994
Comments on “Considerations on the use of time-domain reflectometry (TDR) for
measuring soil moisture content.” by W R Walley.
Journal of Soil Sci. 45, 503-508