Note of clarification about: Field and laboratory calibration and test of TDR and capacitance techniques for indirect measurement of soil water content, by P.N.J. Lane and D.H. Mackenzie, Vol. 39, pp. 1371-1386

Soil Research ◽  
2002 ◽  
Vol 40 (3) ◽  
pp. 555 ◽  
Author(s):  
P. N. J. Lane ◽  
D. H. Mackenzie ◽  
A. D. Nadler
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Calibration Procedure ◽  
Indirect Measurement ◽  
Time Domain Reflectometry ◽  
Data Set ◽  
Laboratory Calibration ◽  
Capacitance Probe ◽  
Note Of Clarification

Time domain reflectometry (TDR) and a frequency domain sensor, the Didcot Capacitance Probe, were tested in the field and laboratory. The results from an undisturbed large core TDR laboratory test found the Topp equation returned a close correspondence to thermogravimetrically derived water content, although there was a slight underestimation. Coefficients of determination and efficiency were >0.98 and 0.92, respectively, for individual cores, and 0.98 and 0.97 for the whole data set. The field exercise revealed the Topp equation to be superior to the laboratory derived equation and other published empirical equations, suggesting the Topp equation to be adequate. A field test of the capacitance probe found poor correspondence between measured and predicted observations of profile point soil water content. Although 81% of the variance was explained by the calibration regression, there was a poor fit to the 1:1 line (E = 0.34), and a non-significant relationship between measured and predicted soil water content for the A horizon. The instrument design proved problematic for use as a determiner of point profile soil water content, and the recommended calibration procedure was impossible in the study site soils.

Field and laboratory calibration and test of TDR and capacitance techniques for indirect measurement of soil water content

Soil Research ◽  
2001 ◽  
Vol 39 (6) ◽  
pp. 1371 ◽  
Author(s):  
P. N. J. Lane ◽  
D. H. Mackenzie
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Calibration Procedure ◽  
Indirect Measurement ◽  
Time Domain Reflectometry ◽  
Large Core ◽  
Data Set ◽  
Laboratory Calibration ◽  
Capacitance Probe

Time domain reflectometry (TDR) and a frequency domain sensor, the Didcot Capacitance Probe, were tested in the field and laboratory. The results from an undisturbed large core TDR laboratory test found the Topp equation returned a close correspondence to thermogravimetrically derived water content, although there was a slight underestimation. Coefficients of determination and efficiency were >0.98 and 0.92, respectively, for individual cores, and 0.98 and 0.97 for the whole data set. The field exercise revealed the Topp equation to be superior to the laboratory derived equation and other published empirical equations, suggesting the Topp equation to be adequate. A field test of the capacitance probe found poor correspondence between measured and predicted observations of profile point soil water content. Although 81% of the variance was explained by the calibration regression, there was a poor fit to the 1:1 line (E = 0.34), and a non-significant relationship between measured and predicted soil water content for the A horizon. The instrument design proved problematic for use as a determiner of point profile soil water content, and the recommended calibration procedure was impossible in the study site soils.

scholarly journals The dielectric calibration of capacitance probes for soil hydrology using an oscillation frequency response model

1998 ◽  
Vol 2 (1) ◽  
pp. 111-120 ◽  
Author(s):  
D. A. Robinson ◽  
C. M. K. Gardner ◽  
J. Evans ◽  
J. D. Cooper ◽  
M. G. Hodnett ◽  
...  
Keyword(s):  
Ionic Conductivity ◽  
Frequency Response ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Time Domain ◽  
Relative Permittivity ◽  
Time Domain Reflectometry ◽  
Physically Based ◽  
Capacitance Probe

Abstract. Capacitance probes are a fast, safe and relatively inexpensive means of measuring the relative permittivity of soils, which can then be used to estimate soil water content. Initial experiments with capacitance probes used empirical calibrations between the frequency response of the instrument and soil water content. This has the disadvantage that the calibrations are instrument-dependent. A twofold calibration strategy is described in this paper; the instrument frequency is turned into relative permittivity (dielectric constant) which can then be calibrated against soil water content. This approach offers the advantages of making the second calibration, from soil permittivity to soil water content. instrument-independent and allows comparison with other dielectric methods, such as time domain reflectometry. A physically based model, used to calibrate capacitance probes in terms of relative permittivity (εr) is presented. The model, which was developed from circuit analysis, predicts, successfully, the frequency response of the instrument in liquids with different relative permittivities, using only measurements in air and water. lt was used successfully to calibrate 10 prototype surface capacitance insertion probes (SCIPS) and a depth capacitance probe. The findings demonstrate that the geometric properties of the instrument electrodes were an important parameter in the model, the value of which could be fixed through measurement. The relationship between apparent soil permittivity and volumetric water content has been the subject of much research in the last 30 years. Two lines of investigation have developed, time domain reflectometry (TDR) and capacitance. Both methods claim to measure relative permittivity and should therefore be comparable. This paper demonstrates that the IH capacitance probe overestimates relative permittivity as the ionic conductivity of the medium increases. Electrically conducting ionic solutions were used to test the magnitude of this effect on the determination of relative permittivity. The response was modelled so that the relative permittivity, independent of ionic conductivity, could be determined in solutions with an electrical conductivity of up to 0.25 S m-1. It was found that a solution EC of less than 0.05 S m-1 had little impact on the permittivity measurement.

Measuring Soil Water Content With Time Domain Reflectometry

Soil Science ◽  
2010 ◽  
Vol 175 (10) ◽  
pp. 469-473 ◽  
Author(s):  
Zhaoqiang Ju ◽  
Xiaona Liu ◽  
Tusheng Ren ◽  
Chunsheng Hu
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Time Domain ◽  
Time Domain Reflectometry

scholarly journals Using an inverse modelling approach to evaluate the water retention in a simple water harvesting technique

2009 ◽  
Vol 6 (3) ◽  
pp. 4265-4306 ◽  
Author(s):  
K. Verbist ◽  
W. M. Cornelis ◽  
D. Gabriels ◽  
K. Alaerts ◽  
G. Soto
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Retention ◽  
Measurement Techniques ◽  
Inverse Modelling ◽  
Model Parameters ◽  
Arid Zones ◽  
Water Harvesting ◽  
Data Set

Abstract. In arid and semi-arid zones runoff harvesting techniques are often applied to increase the water retention and infiltration on steep slopes. Additionally, they act as an erosion control measure to reduce land degradation hazards. Nevertheless, few efforts were observed to quantify the water harvesting processes of these techniques and to evaluate their efficiency. In this study a combination of detailed field measurements and modelling with the HYDRUS-2D software package was used to visualize the effect of an infiltration trench on the soil water content of a bare slope in Northern Chile. Rainfall simulations were combined with high spatial and temporal resolution water content monitoring in order to construct a useful dataset for inverse modelling purposes. Initial estimates of model parameters were provided by detailed infiltration and soil water retention measurements. Four different measurement techniques were used to determine the saturated hydraulic conductivity (Ksat) independently. Tension infiltrometer measurements proved a good estimator of the Ksat value and a proxy for those measured under simulated rainfall, whereas the pressure and constant head well infiltrometer measurements showed larger variability. Six different parameter optimization functions were tested as a combination of soil-water content, water retention and cumulative infiltration data. Infiltration data alone proved insufficient to obtain high model accuracy, due to large scatter on the data set, and water content data were needed to obtain optimized effective parameter sets with small confidence intervals. Correlation between observed soil water content and simulated values was as high as R2=0.93 for ten selected observation points used in the model calibration phase, with overall correlation for the 22 observation points equal to 0.85. Model results indicate that the infiltration trench has a significant effect on soil water storage, especially at the base of the trench.

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