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The solution to the problem of electric measurement of the physical quantity in selective way is to find such an electric property of the medium conditioning it, which is specific to the considered medium. For example, the specific property of molecular oxygen in electrolyte (“soil water”) is small activation energy of electrode reaction of its reduction. It can be concluded that electric measurement of oxygenation may be based on the amperometric measurement of the current of electrode reaction of oxygen molecules reduction (Malicki and Bieganowski [55]). Similarly, concerning the issue of electric measurement of soil salinity, the media conditioning salinity are salts present in soils and the specific property is their ionic form. The ability to transport electric charge by the ions in “soil water” allows the soil to conduct electric current. Therefore the electric measurement of soil salinity should be based on the measurement of its electric conductivity. 2.1.1. Electrical measurement of soil water content Concerning the problem of electric soil water content measurement, the medium conditioning water content is water and its specific property is the polar structure of water molecules (a water molecule has a permanent dipole moment of 1.87 D). Polarity of water molecules is the reason that dielectric permittivity (dielectric constant) of water is much higher than permittivity of soil solid phase (the relative dielectric constant of water in the electric field of frequency below 10 GHz and 18 ºC temperature is 81, while the relative dielectric constant of solid phase is 4 ÷ 5 at the same conditions). The dielectric constant of soil strongly depends on its water content, therefore it may be concluded that electric measurement of soil water content should be based on the measurement of its dielectric constant. The medium conditioning its water content is water and its unique property is the polar structure of water molecules. The real part of water dielectric permittivity (dielectric constant) is much higher than dielectric constant of soil solid phase therefore it can be concluded that electrical measurement of soil water content should be based on the measurement of its dielectric constant. The efforts to measure soil water content indirectly, on the base of the resistance or electrical capacitance between the electrodes inserted into the soil, has been continuously undertaken since the end of nineteen age (Whitney et al. [102]). 2.1.2. Electrical measurement of soil salinity Similarly, referring to the problem of electrical measurement of soil salinity, the medium conditioning its salinity is salt present in the soil and the unique 11
property is their ionic nature. The ability to conduct electrical charge by ions present in the soil water is the reason that the soil conducts current. Therefore, the electrical measurement of soil salinity should be based on the measurement of its electrical conductivity. Soil salinity is expressed by a total concentration of salts in the soil, and practically their ions in the “soil water”. Due to technical reasons connected with the determination of such a defined salinity, its measure by indirect quantity – electrical conductivity of the soil extract, named as a soil electrolyte, which is taken from the soil after its saturation by distilled water (Marshall and Holmes [63]). This procedure proposed by US Salinity Laboratory [94], has been recognized as standard. However this method cannot be used in in situ measurements and also in automatic monitoring systems of soil salinity. The in situ and non-distructive alternative is the measurement of the soil apparent electrical conductivity, EC a , as the basis for determination of the electrical conductivity of the soil electrolyte, EC w (Rhoades et al. [76], Nadler [70]). For this purpose a four-electrode method is often used (Kirkham and Taylor [46]; Gupta and Hanks [35]). It consists in the measurement of the voltage drop along the current, which is forced by other, in relation to measured, pair of supply electrodes. Such a solution enables to avoid disturbances caused by electrochemical polarization of at the interface electrode-electrolyte. However the EC a depends also on soil water content, θ, and to determine EC w it is necessary to measure EC a and θ, simultaneously. Rhoades et al. [76] presented a model relating EC a , EC w and θ as follows: ( a + a ) ekS ekG = ekEθ 0θ 1 + (1) where: a 0 and a 1 are empirical indexes different for various soils and profile layers of the given soil, EC s , is the electrical conductivity of the soil solid phase dependent on the concentration of cations adsorbed on the surface of clay minerals and the presence of ferrite minerals. 12
Page 2 and 3: TDR METHOD FOR THE MEASUREMENT OF W
Page 4 and 5: PREFACE The importance of water for
Page 6 and 7: CONTENTS 1. Status of water as an s
Page 8 and 9: 12.2. New prototype version of FOM/
Page 10 and 11: that stimulate the phenomena and pr
Page 14 and 15: 3. ELECTRICAL MEASUREMENTS METHODS
Page 16 and 17: v = c 1 2L = = ( θ ) n ∆t ε (2)
Page 18 and 19: The TDR probe consists of two waveg
Page 20 and 21: ε a =1 and φ=0.5 the Eq. (10) has
Page 22 and 23: The experiment description is given
Page 24 and 25: Results obtained with the discussed
Page 26 and 27: Notice that at C s = 0, ie when dis
Page 28 and 29: water orientation polarization [s],
Page 30 and 31: Fig. 8. Frequency dispersion of the
Page 32 and 33: The measurements were performed in
Page 34 and 35: 5. EVALUATION OF DIELECTRIC MIXING
Page 36 and 37: ε α = ∑V α iε i (29) i where
Page 38 and 39: where SAND and CLAY are percents of
Page 40 and 41: Below the transition value, the soi
Page 42 and 43: To verify the observations concerni
Page 44 and 45: 6. TEMPERATURE EFFECT ON SOIL DIELE
Page 46 and 47: chamber and the freezer, only one w
Page 48 and 49: The user interface on the main comp
Page 50 and 51: soil sample volumetric water conten
Page 52 and 53: close vicinity of the analyzed obje
Page 54 and 55: process of measurement is non-destr
Page 56 and 57: dielectric permittivity change caus
Page 58 and 59: The values of the refractive index
Page 60 and 61: The relative, ∆n/∆T, and absolu
Page 62 and 63:
Fig. 25. The temperature effect on
Page 64 and 65:
The temperature effect of TDR soil
Page 66 and 67:
The purpose of the above discussion
Page 68 and 69:
( ,25 + T )( 45 + T ) 49 9 f rel =
Page 70 and 71:
8. THE ACCURACY OF SOIL WATER CONTE
Page 72 and 73:
gravimetric method and the soil ref
Page 74 and 75:
where: a 0 ÷ a 6 are coefficients
Page 76 and 77:
values of p F calculated for the re
Page 78 and 79:
eason of this is the fact that wate
Page 80 and 81:
9 ∆θ = 0,2 ⋅10 ⋅ ∆t = 0.00
Page 82 and 83:
values of θ rel for lower values o
Page 84 and 85:
9. COMPARISON OF OPEN-ENDED COAX AN
Page 86 and 87:
ε" = EC ε d " + (82) 2π fε wher
Page 88 and 89:
dielectric permittivity, the dielec
Page 90 and 91:
The applied lumped capacitance mode
Page 92 and 93:
stainless steel wires soldered to t
Page 94 and 95:
ε’ Open Coax and ε b-TDR , exce
Page 96 and 97:
− − The difference of the imagi
Page 98 and 99:
Integrated Circuit) recently introd
Page 100 and 101:
10.2. Electromechanical microwave s
Page 102 and 103:
RF1. Two PIN diodes in series in ea
Page 104 and 105:
The significant aspect of the proto
Page 106 and 107:
visible for lower values of soil el
Page 108 and 109:
In the TDR method the signal propag
Page 110 and 111:
description of functional and techn
Page 112 and 113:
MASTER modules are wireless transce
Page 114 and 115:
time the Real Time Clock module wak
Page 116 and 117:
ase station distinguishes A SLAVE d
Page 118 and 119:
sensor, format the data received fr
Page 120 and 121:
12. SOIL WATER STATUS MONITORING DE
Page 122 and 123:
D-LOG/mpts is a moisture/pressure/t
Page 124 and 125:
For compatibility reasons it uses t
Page 126 and 127:
D-LOG/mts (Fig. 59) is a TDR (Time-
Page 128 and 129:
12.4. FP/m, FP/mts - Field Probe fo
Page 130 and 131:
inside of a separate polyethylene b
Page 132 and 133:
differential water capacity and the
Page 134 and 135:
− maximum number of LP/p probes t
Page 136 and 137:
12.7. LP/t - Laboratory Probe for s
Page 138 and 139:
From the collected data set, after
Page 140 and 141:
25. de Loor G.P.: Dielectric proper
Page 142 and 143:
TDR. Symposium on Time Domain Refle
Page 144 and 145:
100. Whalley W.R.: Considerations o
Page 146 and 147:
Fig. 14. Fig. 15. Fig. 16. Fig. 17.
Page 148 and 149:
Fig. 38. The three-rod TDR probe -
Page 150 and 151:
Fig. 67. A set of LP/ms and LP/p LO
Page 152:
Table 17. An example of the executa
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