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6. TEMPERATURE EFFECT ON SOIL DIELECTRIC PERMITTIVITY- DESCRIPTION OF LABORATORY SETUP AND APPLIED SOFTWARE The purpose of the study, which uses the below described laboratory setup, is to determine the temperature influence on the soil bulk dielectric permittivity, ε b , calculated from the measurement of the EM velocity of propagation in the soil using TDR technique. The final effect is aimed at the adaptation of existing physical models to account for the soil dielectric permittivity change caused by the change of its temperature for mineral soils of variable texture and bulk electrical conductivity. The developed model will help to interpret the influence of selected soil physical parameters on its dielectric properties and will be used in calibration of soil water content and conductivity reflectometric meters. The soil bulk dielectric permittivity, ε b , change with temperature is not fully explained yet (Or and Wraith [72]), but analysing equations (37) and (38) it can be assumed that: − ε b decreases with temperature increase because ε ' decreases following the temperature effect of soil free water, − ε b increases with temperature increase following the release of bound − water molecules, ε b increases with temperature increase following temperature induced increase of soil electrical conductivity, σ dc . Reaching the described objective is requires the collection of experimental data of the selected soil physical properties and developing the general physical model of the temperature effect on soil dielectric permittivity. The tested material consists of mineral soils of variable texture and specific surface area. The complexity of applied experimental methods requires the application of automatic measurement system. It consists of a central computer controlling the sequence and time schedule of the measurement from individual sensors and the temperature in the temperature chambers. The individual sensors are equipped with intelligence in the form of microcontrollers that react on the commands from the central unit and take over the control on the measurement process. The measured data from the individual sensors of non-electrical quantities are converted into digital form and sent back to the central unit for storage. The collected data feed the general physical model of the form ε = f ( θ, T, ECa , ρ, S ), where the arguments of the presented function are: soil water content, temperature, apparent electrical conductivity, bulk density and specific surface area, respectively. 43
6.1. Description of the laboratory setup Reflectometric measurements for the determination of the change of soil samples bulk dielectric permittivity with temperature, water content and electrical conductivity were performed using the setup presented in Fig. 18 and Fig. 19 and described in detail in Skierucha [81]. Below there is a short description of the measurement system. Fig. 18. The experimental setup for the determination of temperature effect on soil dielectric permittivity determined by TDR method The setup consists of three functional modules controlled by PC computer: − oscilloscope frame HP54120 with the TDR unit HP54121T, − self designed and manufactured interface connecting TDR probes to the TDR unit by eight position 0.01 - 2.4 GHz multiplexer [42], reading − selected temperature sensors and controlling the temperature chamber, temperature chamber consisting of a freezer, a fan-heater inside it and an additional fan to minimize temperature gradients inside the chamber. PC compatible computer controlling the dedicated interface by means serial RS232C interface and the oscilloscope by universal GPIB interface, is connected to Internet to monitor the performance of the experiment in the remote way. The application software was written in Visual Basic to provide a user friendly interface for the operator. Temperature of the soil samples was controlled by switching on and off the fan-heater located at the bottom of the temperature 44
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 12 and 13: The solution to the problem of elec
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 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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