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values of θ rel for lower values of θ can be explained by bigger influence of soil solid phase in the effective soil dielectric constant. Table 15. Statistical parameters of ∆θ rel for the set of data with all soil samples under test and the subset of data with soil samples of water contents θ > 0.1. Statistical ∆θ rel parameter model I model III All soil samples under test Mean -0.0418 0.0317 Standard deviation 0.5112 0.3123 Variance 0.2613 0.0975 No of samples 388 388 Confidence Level (95%) 0.0511 0.0312 Soil samples with θ>0.1 Mean -0.0036 -0.0102 Standard deviation 0.1830 0.0771 Variance 0.0335 0.0060 No of samples 328 328 Confidence Level (95%) 0.0198 0.0083 Water in dry soil exists mainly in the form of the particles adsorbed by solid phase. In this condition water molecules are not as easy to polarize as in free water condition. Therefore TDR soil water content measurement should underestimate the real values as compared to thermo-gravimetric method of soil water content determination. This effect should be more acute for fine soils. Fig. 33. Sensitivity of model III on the soil density, ρ, in relation to the soil, θ. 81
Also the error coming from the hardware, which is constant is more visible for low water contents, according to (80). The relative error of TDR water content values increases practically to infinity when soil water content tends to zero value. Table 15 presents the comparison of statistics for relative errors of TDR water content calculated from model I and model III. For soil water contents above 0.1 the standard deviation of ∆θ rel is about four times smaller than for the whole range of θ. The sensitivity of TDR moisture on the soil density values calculated according to model III and expressed as ∂ θTDR / ∂ ρ on the base of (76) is shown in Fig. 33. We see that neglecting the change of soil density of 0.1 g·cm -3 results in the TDR water content determined error of ∆θ TDR = 0,0064 for dry soil and ∆θ TDR = 0,012 for the soil with the water content value of 0.5. 8.3. Conclusions Soil solid phase influences the electromagnetic wave velocity (and consequently its dielectric constant) in soil in the statistically significant way. This influence makes the reflectometric technique, in soil water content measurement application, not selective. Soil density or porosity represents the solid phase influence on its dielectric constant measured by TDR. Inclusion of this influence in the calibration formulae of TDR method makes the reflectometric method of soil water content measurements more selective and decreases the absolute error of its measurement by the factor of two. The error of TDR water content determination originates mainly from the correlation imperfections. The TDR hardware and software sources of TDR water content error may be visible in the lower range of soil water content values. 82
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TDR METHOD FOR THE MEASUREMENT OF W
Page 4 and 5:
PREFACE The importance of water for
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CONTENTS 1. Status of water as an s
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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
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v = c 1 2L = = ( θ ) n ∆t ε (2)
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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 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
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From the collected data set, after
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25. de Loor G.P.: Dielectric proper
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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
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Table 17. An example of the executa
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