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to Eq. (43) significantly decreased the influence opf temperature and the corrected
values were: n (6 °C) = 8.06 do n (12 °C) = 8.02.
Table 9 shows the regression coefficients for the relation n(T ) applied for the
measurements on mineral soils, illustrated in Fig. 25. These coefficients reflect
the susceptibility of the refractive index on temperature dn/dT.
For the presented measurements and tested soils this susceptibility changed in
the following range:
− 0.0105 <
dn
dT
< 0.0008 deg
−1
(49)
depending on the soil water content and soil type.
Table 9.
Regression coefficients in the relation n(T )=a 0 +a 1 T for the tested mineral soils without
and after the application of correction (43)
θ
without
correction
x10 -5
a 1 a 0
with
without
correction
x10 5 correction
with
correction
0.006 30 40 1.65 1.65
sand 0.171 -250 90 3.06 2.99
0.344 -1050 -370 4.98 4.84
0.019 80 120 1.70 1.69
silt 0.324 -370 280 4.52 4.65
0.425 -490 360 5.47 5.64
0.021 50 90 1.72 1.71
clay 0.244 30 520 3.26 3.36
0.492 4 990 5.66 5.86
Fig. 25 presents the results of measurements on three mineral soils described
in Table 7, each of them having three different water contents. The temperature
influences significantly on the soil refractive index, n, and this influence increases
with the soil volumetric water content.
For clay soil the refractive index, n, change with temperature id different than
for san or silt soil. It does not decrease with the temperature increase. This
behavior can be explained by the release of molecular water (bound by clay soil
particles) with temperature increase. The dielectric constant of bound water is
about 20 times lower than free water (Dirksen and Dasberg [27]) and its value is
comparable to the value of dielectric constant of ice, ie about 3.2.
60