Delta-T HH2, User Manual

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About Soil Parameters a0 & a1 Moisture Meter User Manual 4.0
About Soil Parameters a0 & a1
Theory
Delta-T soil moisture sensors respond to the soil dielectric constant ε, which is
strongly dependent on the water content. Several authors:- Whalley , and White,
Knight, Zeggelin and Topp, have shown that there is a simple relationship between
the complex refractive index (equivalent to the square root of ε ), and the volumetric
water content ,
θ,
as follows:
θ ε
× + = 1 0
a a
About a0 and a1
These soil specific parameters are unique for each soil type. They are used with a
linearisation table, in the HH2, to convert the sensor output, in mV, into soil moisture
readings.
mV vε
68 1.476
101 1.621
137 1.792
201 2.089
Soil Type a0 a1
Mineral 1.6 8.4
Organic 1.3 7.7
Other user * user *
user * : optional user supplied soil calibration
Sensor Type
Soil parameters
Sensor output
(mV)
Square root of
permittivity
vε
1 / ) 0 (
a a
− =
ε θ
Volumetric
water content
θ
Linearisation
Table