THE MEASUREMENT OF SOIL WATER CONTENT USING A PORTABLE TDR HAND PROBE

1984 ◽  
Vol 64 (3) ◽  
pp. 313-321 ◽  
Author(s):  
G. C. TOPP ◽  
W. D. ZEBCHUK ◽  
J. L. DAVIS ◽  
W. G. BAILEY
Keyword(s):  
Water Content ◽  
Transmission Lines ◽  
Time Domain ◽  
Surface Soil ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Separate Experiment ◽  
Parallel Transmission ◽  
The Time Domain

The time-domain reflectrometry (TDR) technique had previously been shown to measure the volumetric water content of soil accurately when applied to long-term installations of parallel transmission lines. In this study a hand probe was used with a portable TDR instrument to measure water content of soil down the wall of soils pits to a depth greater than 1 m. In a separate experiment the water content of the surface soil at two sites was measured repeatedly in increasing depth increments of 50 mm to 300 mm. The TDR measured values were compared with values obtained by a gravimetric determination on a sample of soil. The TDR gave values that were calculated at the time of measurement in the field. TDR measured values were as accurate and precise as those from gravimetric samples. Key words: Volumetric water content, soil, time domain reflectometry

Using time domain reflectometry in triaxial testing

2000 ◽  
Vol 37 (6) ◽  
pp. 1325-1331
Author(s):  
J LH Grozic ◽  
M E Lefebvre ◽  
P K Robertson ◽  
N R Morgenstern
Keyword(s):  
Cyclic Loading ◽  
Water Content ◽  
Time Domain ◽  
Void Ratio ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Degree Of Saturation ◽  
Triaxial Testing ◽  
Empirical Correlations ◽  
Static And Cyclic Loading

Time domain reflectometry (TDR) can be used to determine the volumetric water content of soils. This note describes the utilization of a TDR miniprobe in triaxial testing. The TDR performance was examined with a series of tests that not only proved its reliability but also resulted in two empirical correlations. Using these correlations, the degree of saturation and volumetric water content during triaxial testing could be determined. The TDR was then put to use in a laboratory program designed to investigate the response of loose gassy sand under static and cyclic loading. Because of the TDR measurements it was possible to determine the degree of saturation and void ratio of the gassy specimens. The TDR miniprobe proved to be accurate, simple to use, and inexpensive to build.Key words: time domain reflectometry, TDR, triaxial testing, gassy, unsaturated.

scholarly journals Construction and calibration of TDR probes for volumetric water content estimation in a Distroferric Red Latosol

2013 ◽  
Vol 33 (5) ◽  
pp. 919-928 ◽  
Author(s):  
Rosimaldo Soncela ◽  
Silvio C. Sampaio ◽  
Marcio A. Vilas Boas ◽  
Maria H. F. Tavares ◽  
Adriana Smanhotto
Keyword(s):  
Water Content ◽  
Irrigation Management ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Coefficient Of Determination ◽  
Calibration Model ◽  
Advantages And Disadvantages ◽  
Disturbed Soil ◽  
Red Latosol ◽  
The Time Domain

The determination of volumetric water content of soils is an important factor in irrigation management. Among the indirect methods for estimating, the time-domain reflectometry (TDR) technique has received a significant attention. Like any other technique, it has advantages and disadvantages, but its greatest disadvantage is the need of calibration and high cost of acquisition. The main goal of this study was to establish a calibration model for the TDR equipment, Trase System Model 6050X1, to estimate the volumetric water content in a Distroferric Red Latosol. The calibration was carried out in a laboratory with disturbed soil samples under study, packed in PVC columns of a volume of 0.0078m³. The TDR probes were handcrafted with three rods and 0.20m long. They were vertically installed in soil columns, with a total of five probes per column and sixteen columns. The weightings were carried out in a digital scale, while daily readings of dielectric constant were obtained in TDR equipment. The linear model θν = 0.0103 Ka + 0.1900 to estimate the studied volumetric water content showed an excellent coefficient of determination (0.93), enabling the use of probes in indirect estimation of soil moisture.

scholarly journals CARACTERIZAÇÃO DA DISTRIBUIÇÃO DA ÁGUA NO SOLO PARA IRRIGAÇÃO POR GOTEJAMENTO

Irriga ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 564-577 ◽  
Author(s):  
Leonardo Do Nascimento Lopes ◽  
Elton Martins ◽  
Bruno De Lima Santoro ◽  
Claudinei Fonseca Souza
Keyword(s):  
Water Content ◽  
Time Domain ◽  
Water Distribution ◽  
Water Storage ◽  
Time Domain Reflectometry ◽  
Wetting Front ◽  
Applied Water ◽  
Flow Rates ◽  
Abstract Knowledge ◽  
The Time Domain

CARACTERIZAÇÃO DA DISTRIBUIÇÃO DA ÁGUA NO SOLO PARA IRRIGAÇÃO POR GOTEJAMENTO  Leonardo do Nascimento Lopes1; Elton Martins2; Bruno de Lima Santoro2; Claudinei Fonseca Souza31Universidade de Taubaté, Unitau, Taubaté, SP,  [email protected] Engenharia Civil e Ambiental, Universidade de Taubaté, Taubaté, Unitau, SP 3Departamento de Recursos Naturais e Proteção Ambiental, Universidade Federal São Carlos, São Carlos, SP  1 RESUMO O conhecimento da distribuição da água no solo é de grande importância para a agricultura, uma vez que a água é um dos fatores que mais influenciam o rendimento das culturas. Existem muitas técnicas utilizadas para o monitoramento do conteúdo de água do solo, a reflectometria domínio do tempo (TDR) tem sido difundida entre os pesquisadores por apresentar várias vantagens, entre as quais a determinação em tempo real e a possibilidade de leituras automatizadas. O principal objetivo desta pesquisa foi avaliar a distribuição da água no perfil de um Latossolo Vermelho-Amarelo. Sondas de Reflectometria no domínio do Tempo (TDR) foram utilizadas para monitorar a distribuição de água no solo aplicada através de gotejadores de fluxo constante nas taxas de 2, 4 e 8 Lh-1. Considerando os resultados de diferentes perfis, observa-se um maior armazenamento da água próximo do gotejador diminuindo progressivamente para frente de molhamento. Aproximadamente, um terço da água aplicada (33%) foi armazenado na primeira camada (0-0,10 m) para todos os ensaios. Comparando diferentes taxas de aplicação, observa-se maior armazenamento de água para o gotejador de 8L h-1, com 30, 33 e 34% de água aplicada acumulada na primeira camada (0-0.10 m) para gotejadores de 2, 4 e 8L h-1, respectivamente. Os resultados sugerem que, com base no volume e frequência utilizada neste experimento, seria vantajoso aplicar pequenas quantidades de água em intervalos mais frequentes para reduzir perdas por percolação. UNITERMOS: TDR, conteúdo de água, bulbo molhado  LOPES, L. N.; MARTINS, E.; SANTORO, B. L.; SOUZA, C. F.WATER DISTRIBUTION CHARACTERIZATION IN SOIL FOR DRIP IRRIGATION   2 ABSTRACT Knowledge of water distribution in soil is of great importance to agriculture, since water is one of the factors that most influence the yield of crops. There are many techniques used to monitor soil water content. The time domain reflectometry (TDR) has been widespread among researchers because it presents several advantages, among which the determination in real time and possibility of automated readings. The main goal of this research was to evaluatethe water distribution in a profile of Red-Yellow Oxisol. Time domain reflectometry (TDR) probes were used to monitor the water distribution from drippers discharging at constant flow rates of 2, 4 and 8 Lh-1 in soil. Considering results from different profiles, we observed greater water storage near the dripper decreasing gradually towards the wetting front. About one third of the applied water (33%) was stored in the first layer (0-0.10 m) for all experiments. Comparing different dripper flow rates, we observed higher water storage for 8 L h-1, with 30, 33 and 34% of applied water accumulating in the first layer (0-0.10m) for dripper flow rates of 2, 4 and 8 L h-1, respectively. The results suggest that based on the volume and frequency used in this experiment, it would be advantageous to apply small amounts of water at more frequent intervals to reduce deep percolation losses of applied water. KEYWORDS: TDR, water content, wetted soil volume

Use of Time-Domain Reflectometry (TDR) to measure the water-content of sandy soils

Soil Research ◽  
1995 ◽  
Vol 33 (2) ◽  
pp. 265 ◽  
Author(s):  
PJ Gregory ◽  
R Poss ◽  
J Eastham ◽  
S Micin
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Transmission Lines ◽  
Time Domain ◽  
Water Storage ◽  
Sandy Soils ◽  
Time Domain Reflectometry ◽  
Soil Water Storage ◽  
Use Of Time ◽  
Daily Evaporation

We investigated the potential sources of error when using time domain reflectometry (TDR) to measure the water content of sandy soils and evaluated the technique as a means of measuring evaporation from columns of soil and changes in soil water storage beneath crops. Inaccurate depth location of the transmission lines or the development of a hole at the tip of the transmission lines introduced an error about 10 times larger than the errors associated with hardware and software. Calibration in two sandy soils gave a curve of similar shape to that found by others except for values of dielectric constant < 6 when measured values of water content were less than those expected. Daily evaporation from soil columns measured by weighing and with TDR showed large differences between the two techniques (up to 32%) but compensating errors over time allowed cumulative evaporation to be estimated with TDR to within 6.6% of that determined by weighing over a 162 h period. Under field conditions, the agreement between TDR and neutron probe measures of changes in soil water storage in the upper 0.3 m was good and generally within 10% over both 14 day and longer periods.

scholarly journals Locating the frozen–unfrozen interface in soils using time-domain reflectometry

1982 ◽  
Vol 19 (4) ◽  
pp. 511-517 ◽  
Author(s):  
T. H. W. Baker ◽  
J. L. Davis ◽  
H. N. Hayhoe ◽  
G. C. Topp
Keyword(s):  
Transmission Lines ◽  
Time Domain ◽  
Freezing Temperature ◽  
Time Domain Reflectometry ◽  
Temperature Measurements ◽  
Soil Freezing ◽  
Electromagnetic Pulses ◽  
The Time Domain ◽  
Time Domain Reflectometer ◽  
Liquid And Solid Phases

The time-domain reflectometry technique was compared with the temperature measurement method for locating the frozen–unfrozen interface in water and sandy soils. This technique depends on the high-frequency (1–1000 MHz) electrical properties of water that change significantly and abruptly between the liquid and solid phases. Parallel wire transmission lines were inserted into the soil to guide electromagnetic pulses produced by a time-domain reflectometer (TDR). The frozen–unfrozen interface produced reflections measured by the TDR which were in turn used to locate the interface as it moved along the transmission line. In the laboratory it was possible to locate the interface using the TDR to within ±0.5 cm and in the field to within ±2.4 cm. These errors were equal to those associated with the temperature measurements. Keywords: soil freezing, temperature measurements, dielectric constant, time-domain reflectometry.

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