CALIBRAÇÃO DE UM EQUIPAMENTO TDR EM CONDIÇÕES DE CAMPO

CALIBRAÇÃO DE UM EQUIPAMENTO TDR EM CONDIÇÕES DE CAMPO Rosangela Villwock; Maria Hermínia Ferreira Tavares; Márcio Antônio Vilas BoasCentro de Ciências Exatas e Tecnológicas, Universidade Estadual do Oeste do Paraná, Cascavel , PR, [email protected] 1 RESUMO A utilização da Reflectometria no Domínio do Tempo (TDR) tornou-se um método muito bem aceito nas avaliações de teores de água no solo. Todavia, para utilização do equipamento há a necessidade de calibrá-lo para que se obtenha valores acurados de umidade volumétrica, devendo-se sempre respeitar as peculiaridades de cada solo para que o processo de calibração ocorra de forma correta. O objetivo deste trabalho foi calibrar o equipamento TDR em condições de campo, especificamente para um Latossolo Vermelho distroférrico, localizado no Núcleo Experimental de Engenharia Agrícola, Universidade Estadual do Oeste do Paraná, Campus de Cascavel. O modelo polinomial cúbico foi o que melhor se ajustou aos dados para a calibração do equipamento. UNITERMOS: constante dielétrica aparente, modelo polinomial cúbico, umidade do solo. VILLWOCK, R.; TAVARES, M. H. F.; VILLAS BOAS, M. A.TDR EQUIPMENT CALIBRATION IN FIELD CONDITIONS 2 ABSTRACT The use of Time Domain Reflectometry (TDR) has become a very well accepted method to evaluate soil water content. However, for the equipment utilization there is the need to calibrate it to obtain accurate values of volumetric soil water content, always respecting the soil characteristics. The objective of this research was to calibrate the TDR equipment in field conditions, specifically for a Rhodic Hapludox, at the UNIOESTE Experimental Station of Agricultural Engineering, in the campus of Cascavel, State of Parana. The cubic polynomial model was the model that best adjusted the data for the calibration of the equipment. KEYWORDS: apparent dielectric constant, cubic polynomial model, soil moisture.

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Time Domain Reflectometry to Measure Volumetric Soil Water Content

Principles of Soil and Plant Water Relations ◽

10.1016/b978-012409751-3/50013-x ◽

2005 ◽

pp. 187-205 ◽

Cited By ~ 4

Author(s):

M.B. Kirkham

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Time Domain ◽

Time Domain Reflectometry ◽

Volumetric Soil Water Content ◽

Volumetric Soil Water

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The effect of soil electrical conductivity on moisture determination using time-domain reflectometry in sandy soil

Canadian Journal of Soil Science ◽

10.4141/s98-089 ◽

2000 ◽

Vol 80 (1) ◽

pp. 13-22 ◽

Cited By ~ 41

Author(s):

Z. J. Sun ◽

G. D. Young ◽

R. A. McFarlane ◽

B.M. Chambers

Keyword(s):

Electrical Conductivity ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Saline Soil ◽

Time Domain Reflectometry ◽

Propagation Time ◽

Soil Electrical Conductivity ◽

Volumetric Soil Water Content ◽

Volumetric Soil Water

A series of laboratory experiments was conducted, in order to systematically explore the effect of soil electrical conductivity on soil moisture determination using time domain reflectometry (TDR). A Moisture Point MP-917 soil moisture instrument (E.S.I. Environmental Sensors Inc., Victoria, BC, Canada) was used to measure propagation time (time delay) of a step function along a probe imbedded in fine sand with different moisture and salinity. The volumetric soil water content was independently determined using a balance. With the help of the diode-switching technique, MP-917 could detect the reflection from the end of the probe as the electrical conductivity of saturated soil extract (ECe) increased to 15.29 dS m−1. However, the relationship between volumetric soil water content and propagation time expressed as T/Tair (the ratio of propagation time in soil to that in air over the same distance) deviated from a linear relationship as the conductivity exceeded 3.72 dS m−1. At the same water content, the time delay in a saline soil was longer than that in a non-saline soil. This leads to an over-estimation of volumetric soil water content when the linear calibration was applied. A logarithmic relationship between volumetric soil water content and T/Tair has been developed and this relation includes soil electrical conductivity as a parameter. With this new calibration, it is possible to precisely determine the volumetric water content of highly saline soil using TDR. Key words: Time domain reflectometry, time delay, bulk electrical conductivity (σ), volumetric soil water content (θ), relative permittivity or dielectric constant (εr), propagation velocity Vp

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CORRECTING SOIL VOLUMETRIC WATER CONTENTS FROM A DIRECT-READING TIME DOMAIN REFLECTOMETRY INSTRUMENT (IRAMS)

Canadian Journal of Soil Science ◽

10.4141/cjss89-070 ◽

1989 ◽

Vol 69 (3) ◽

pp. 701-704 ◽

Cited By ~ 1

Author(s):

G. C. TOPP ◽

J. L. B. CULLEY

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Time Domain ◽

Computer Software ◽

Time Domain Reflectometry ◽

Direct Reading ◽

Volumetric Soil Water Content ◽

Linear Correction

Determination of volumetric soil water content (θ) using time domain reflectometry (TDR) is well established. A commercially available instrument (IRAMS) (the IRAMS (Instrument for Reflectometry Analysis of Moisture in Soils) is a trademark registered by Foundation Instruments Inc. of Ottawa) is now available which incorporates computer software, thus providing direct readouts of θ. A field study of the operation of the IRAMS showed that it operates consistently and repeatedly. The IRAMS values were higher but related linearly to those obtained using a TDR cable tester and manual calculations of travel times. A linear correction of the IRAMS readings is proposed and possible causes are suggested for the observed deviations from expected values. Key words: Time domain, reflectometry, soil water content, field

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Sampling and TDR probe insertion in the determination of the volumetric soil water content

Revista Brasileira de Ciência do Solo ◽

10.1590/s0100-06832003000400001 ◽

2003 ◽

Vol 27 (4) ◽

pp. 575-582 ◽

Cited By ~ 6

Author(s):

W. G. Teixeira ◽

G. Schroth ◽

J. D. Marques ◽

Bernd Huwe

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Gravimetric Method ◽

Time Domain Reflectometry ◽

Volumetric Soil Water Content ◽

Undisturbed Samples ◽

Similar Accuracy ◽

Volumetric Soil Water

Volumetric soil water content (theta) can be evaluated in the field by direct or indirect methods. Among the direct, the gravimetric method is regarded as highly reliable and thus often preferred. Its main disadvantages are that sampling and laboratory procedures are labor intensive, and that the method is destructive, which makes resampling of a same point impossible. Recently, the time domain reflectometry (TDR) technique has become a widely used indirect, non-destructive method to evaluate theta. In this study, evaluations of the apparent dielectric number of soils (epsilon) and samplings for the gravimetrical determination of the volumetric soil water content (thetaGrav) were carried out at four sites of a Xanthic Ferralsol in Manaus - Brazil. With the obtained epsilon values, theta was estimated using empirical equations (thetaTDR), and compared with thetaGrav derived from disturbed and undisturbed samples. The main objective of this study was the comparison of thetaTDR estimates of horizontally as well as vertically inserted probes with the thetaGrav values determined by disturbed and undisturbed samples. Results showed that thetaTDR estimates of vertically inserted probes and the average of horizontally measured layers were only slightly and insignificantly different. However, significant differences were found between the thetaTDR estimates of different equations and between disturbed and undisturbed samples in the thetaGrav determinations. The use of the theoretical Knight et al. model, which permits an evaluation of the soil volume assessed by TDR probes, is also discussed. It was concluded that the TDR technique, when properly calibrated, permits in situ, nondestructive measurements of q in Xanthic Ferralsols of similar accuracy as the gravimetric method.

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Measurement of soil water content using the combined time-domain reflectometry – thermal conductivity probe

Canadian Geotechnical Journal ◽

10.1139/t87-016 ◽

1987 ◽

Vol 24 (1) ◽

pp. 160-163 ◽

Cited By ~ 5

Author(s):

T. H. W. Baker ◽

L. E. Goodrich

Keyword(s):

Thermal Conductivity ◽

Dielectric Constant ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Time Domain ◽

Empirical Relation ◽

Time Domain Reflectometry ◽

Apparent Dielectric Constant ◽

Water Contents

A two-pronged metal probe measures the thermal conductivity and apparent dielectric constant of soils in the laboratory and in the field. One prong acts as a transient line heat source probe in measuring thermal conductivity. The apparent dielectric constant of the soil is determined by the time-domain reflectometry (TDR) technique, using both prongs as a parallel transmission line. Volumetric water content is determined from the apparent dielectric constant, making use of an empirical relation valid for most soils. For volumetric water contents above about 8%, the apparent dielectric constant shows a strong dependence on water content and relatively small changes can be measured; sensitivity increases with water content. For volumetric water contents less than 8%, a soil-dependent empirical relation between water content and thermal conductivity has been developed that is most sensitive at lower water contents. The combined probe provides a means of monitoring the water content of soils over a wide range of values, in the field and in the laboratory. Key words: soil water content, time-domain reflectometry, thermal conductivity.

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ESTIMATES OF SOIL WATER CONTENT USING GROUND PENETRATING RADAR IN FIELD CONDITIONS

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v33i3.940 ◽

2015 ◽

Vol 33 (3) ◽

pp. 389 ◽

Cited By ~ 1

Author(s):

Marcelo Jorge Luz Mesquita ◽

José Gouvêa Luiz ◽

José de Paulo Rocha da Costa

Keyword(s):

Soil Moisture ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Wave Velocity ◽

Ground Penetrating Radar ◽

Time Domain Reflectometry ◽

Field Conditions ◽

Calibration Equation ◽

Ground Penetrating

ABSTRACT. Electromagnetic methods play an important role in the study of soil water content, mainly because electromagnetic properties in the shallow subsurface area are primarily controlled by the presence of water. This work analyzes the effectiveness of Ground Penetrating Radar (GPR) as a tool for estimating soil water content in field conditions, introduces a calibration equation to estimate average soil moisture of the area studied from the analysis of GPR wave velocity, and evaluates the process used to create it. Methodologies for collecting GPR data seeking the determination of soil moisture from the velocity of the electromagnetic wave and the use of equations proposed in the literature, Topp and Roth, are also discussed. The GPR common-offset methodology (400 MHz antennas) was utilized in a study in Cuiarana, Salin´opolis, Par´a State, in northern Brazil and the resulting data compared with data from TDR (Time Domain Reflectometry) (0.12 m double probe) methodology. The data were then statistically analyzed enabling the establishment of a calibration equation for water content determination in terms of electromagnetic wavevelocity obtained with GPR. The study successfully showed the feasibility and limitations of estimating water content using GPR. Also is discussed the possibility of calibration equation to the soil water content analysis with GPR data using, as parameter, data obtained by other indirect method, in this case, the TDR.Keywords: soil water content, relative permittivity, GPR, TDR, wave velocity. RESUMO. Os métodos eletromagnéticos são uma importante ferramenta no estudo da umidade do solo, principalmente porque as propriedades eletromagnéticas da subsuperfície rasa são controladas pela presença de água. Este trabalho, além de analisar a eficácia do Radar de Penetração no Solo (GPR) como ferramenta de medição da umidade do solo in situ sob condições de campo não controladas, introduz uma equação de calibração para estimar a umidade do solo da área estudada a partir da análise da velocidade da onda do GPR e avalia o processo da sua criação. São também discutidas as metodologias comumente empregadas na coleta de dados com o GPR, visando a determinação da umidade do solo a partir da velocidade da onda eletromagnética, assim como a utilização das equações propostas na literatura, Topp e Roth. A metodologia common-offset (GPR com antenas de 400 MHz) foi empregada em um estudo realizado em Cuiarana, município de Salinópolis, Pará, no norte do Brasil e os dados comparados com medidas de umidade realizadas com TDR (sonda dupla de 0,12 m). Os dados foram estatisticamente correlacionados permitindo o estabelecimento de uma equação de calibração para a determinação de umidade em termos da velocidade da onda eletromagnética obtida com o GPR. O estudo demonstrou com sucesso a viabilidade, a rapidez e as limitações do GPR na estimativa do conteúdo de água no solo. Também é discutida a possibilidade da calibração de equação para análise de umidade com o GPR usando como parâmetro dados obtidos por outro método indireto, neste caso, o TDR.Palavras-chave: umidade do solo, permissividade relativa, GPR, TDR, velocidade da onda.

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Effect of inter-row cultivation on soil carbon dioxide emission in a peach plantation

Agrokémia és Talajtan ◽

10.1556/agrokem.59.2010.1.19 ◽

2010 ◽

Vol 59 (1) ◽

pp. 157-164 ◽

Cited By ~ 1

Author(s):

E. Tóth ◽

Cs. Farkas

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Carbon Dioxide Emission ◽

Nutrient Content ◽

Soil Disturbance ◽

Biological Properties ◽

Soil Tillage ◽

Favourable Effect ◽

Volumetric Soil Water Content

Soil biological properties and CO2emission were compared in undisturbed grass and regularly disked rows of a peach plantation. Higher nutrient content and biological activity were found in the undisturbed, grass-covered rows. Significantly higher CO2fluxes were measured in this treatment at almost all the measurement times, in all the soil water content ranges, except the one in which the volumetric soil water content was higher than 45%. The obtained results indicated that in addition to the favourable effect of soil tillage on soil aeration, regular soil disturbance reduces soil microbial activity and soil CO2emission.

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