ekS - Instytut Agrofizyki im. Bohdana DobrzaÅskiego PAN w Lublinie ...
ekS - Instytut Agrofizyki im. Bohdana DobrzaÅskiego PAN w Lublinie ...
ekS - Instytut Agrofizyki im. Bohdana DobrzaÅskiego PAN w Lublinie ...
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where: n w is the free water refractive index at 20 °C, n 20 is the soil refractive index<br />
at 20 °C, ∆n(T ) is its temperature dependent correction, f a , f s are volumetric<br />
fractions of soil air and solid phases, respectively.<br />
The soil water content, θ = θ 20 , in Eq. (42) is determined grav<strong>im</strong>etrically in<br />
laboratory conditions or using TDR soil water content measurement method<br />
appliued for the soil at 20°C, ie in TDR meters calibration conditions. The values<br />
of the refractive index, n T , for soils are determined at T temperature can be<br />
corrected to the values at 20 °C, n 20 , according to the Eq. (42), which can be<br />
rewritten as:<br />
n<br />
( d(<br />
) 1)<br />
20= n −<br />
20<br />
nw<br />
T −<br />
T<br />
θ (43)<br />
As the dielectric soil water content measurement is based on the calibration<br />
formula θ = f (n), the TDR calculated soil water content depend on its<br />
temperature:<br />
T<br />
( ) = θ( n ∆n(<br />
))<br />
θ = θ +<br />
(44)<br />
n T<br />
20<br />
T<br />
For linear shape of the calibration formula the following is true:<br />
dθ<br />
dθ<br />
θ<br />
T<br />
= θ ( n20 + ∆n( T )) = θ<br />
20<br />
+ ∆n<br />
= θ<br />
20<br />
+ θ<br />
20<br />
⋅ nw<br />
( d ( T ) − 1) (45)<br />
dn dn<br />
Rewriting the Eq. (45) we can receive the TDR determined soil water content,<br />
θ 20 , corrected to its value at 20°C:<br />
θT<br />
θ<br />
20<br />
=<br />
(46)<br />
dθ<br />
1 +<br />
n w<br />
( d ( T ) −1) ⋅ dn<br />
The above corrections based on the temperature change affecting the soil free<br />
water and applied to the soil water content values determined by TDR<br />
measurement method will be verified below using exper<strong>im</strong>ental data.<br />
7.3. Materials and methods<br />
The influence of temperature on the refractive index, n, of the EM waves was<br />
tested on the saturated peat soil and three mineral soils with texture presented in<br />
Table 7: sand, silt and clay.<br />
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