Frequency domain analysis of time domain reflectometry waveforms: 1. Measurement of the complex dielectric permittivity of soils

Heimovaara, T.J.

doi:10.1029/93wr02948

Cited by 191 publications

(178 citation statements)

References 20 publications

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“…This is quite low compared to the K values measured up to 4 MHz frequency ( Figure 5). The TDR instrument (TDR1502C) uses a step pulse that contains frequencies from 20 kHz to 1.5 GHz [Heimovaara, 1994]. The dielectric constant of the epoxy-ceramic appears to be lower than expected at these higher frequencies.…”

Section: Results and Discussion Of Effect Of High Dielectric Coatingmentioning

confidence: 99%

High dielectric insulation coating for time domain reflectometry soil moisture sensor

Fujiyasu

Pierce

Fan

et al. 2004

Water Resources Research

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Insulation coating is often applied to time domain reflectometry (TDR) soil moisture sensors to reduce the conduction loss of energy. However, because of low dielectric constants of common plastic insulation materials, sensitivity is reduced, and the measurements are strongly dependent on coating thickness. Analytical studies clearly showed that these unwanted features could be mitigated if a high dielectric material is used for coating. An epoxy‐ceramic nanocomposite was selected as a high dielectric insulation material because of its high dielectric constant and high adhesion. Experimental work using this composite indicated that the material has the potential to be used as a high dielectric coating for TDR soil moisture probes. On the basis of the results of these analytical and experimental studies a framework for designing an improved epoxy‐ceramic composite for coating TDR soil moisture sensors is suggested.

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Section: Results and Discussion Of Effect Of High Dielectric Coatingmentioning

confidence: 99%

High dielectric insulation coating for time domain reflectometry soil moisture sensor

Fujiyasu

Pierce

Fan

et al. 2004

Water Resources Research

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“…The sampling interval is determined by the frequency bandwidth of the TDR measurement system. For the Tektronix 1502B cable tester it was determined to be from dc up to 1.5 GHz [Heimovaara, 1994]. The sample length is selected such that a steady state is reached at the end of the TDR waveform, which means the waveform should achieve a constant value.…”

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confidence: 99%

Theoretical model of a multisection time domain reflectometry measurement system

Feng

Lin²,

Deschamps

et al. 1999

Water Resources Research

122

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Abstract. A multisection model is presented to simulate electromagnetic wave propagation in an unmatched time domain reflectometry (TDR) probe and layered soil system. The model uses a linear-time-invariant feedback system to model each section and links each section in a bottom-up fashion. Multiple sections can be incorporated in this model by a simple extension of a single-section system. An unmatched TDR probe system is modeled by dividing it into equivalent sections and matching the simulated waveform with the actual waveform. The excellent match between the simulated and the recorded waveforms verifies the model. This model eliminates the requirement of a matched 50-12 probe handler in probe design for dielectric measurement. It can also be used to assist probe design and TDR data interpretation. The reflected waveforms in layered soil specimens are modeled, and the simulated waveforms are compared to those obtained from experiments. The method of using apparent dielectric constant to obtain average volumetric water content is examined for the layered soil system. The results show that apparent dielectric constant is applicable for the measurement of average volumetric water content for a layered soil, but caution has to be used when interpreting the waveforms. The TDR method consists of two parts: (1) the physical measurement system that includes the TDR apparatus, probe, and other equipment leading to the generation of a consistent TDR waveform and (2) the interpretation of the TDR waveform including its rclationshi• to the desired material propcrty. The success of the interpretation is the key to applying this technology. Tooeoe et al. [1980] The electromagnetic properties of a material are characterized by three parameters: (1) dielectric permittivity e, (2) electrical conductivity tr, and (3) magnetic permeability/x. In general, these parameters are functions of frequency. However, for materials like soils t•e magnetic permeability differs from magnetic permeability of free space/x o by a negligible fraction, and the frequency dependency of conductivity can be neglected. Owing to the dipole polarization mechanism of water, wet soil is a dielectric material that h as a frequency-dependent complex relative permitfivity:2,n-f 6'r(f) 6r ( Analysis of a Typical TDR Measurement SystemA typical TDR measurement system consists of a cable test device, which sends out a step (or other shape) EM wave through a pulse generator and records the incident and reflection signal with an oscilloscope, and a probe that acts as a waveguide to transmit the EM wave into the soil specimen. A step wave or impulse wave is usually used in order to obtain recognizable reflections at the soil surface and the end of the probe.Transmission line theory is used to model the TDR measurement system in which the field structure in the transmission line is assumed to be of transverse electromagnetic mode (TEM). Owing to the special structure of TEM, (5) Scatter Function for Multisection TDR Measurement SystemDuring field measurement i...

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“…Extensive reviews of TDR applied to soil moisture determination can be found in [55] and [54]. Frequency domain reflectometry (FDR) uses the same principle as TDR, but analyzes the reflected waveform in the frequency domain, enabling the determination of frequency dependent complex dielectric permittivity [56]. This facilitates the separation of probe response and soil response and enables better extraction of useful information [57].…”

Section: Time Domain Reflectometrymentioning

confidence: 99%

Soil Moisture & Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives

et al. 2013

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Moisture content in the soil and snow in the alpine environment is an important factor, not only for environmentally oriented research, but also for decision making in agriculture and hazard management. Current observation techniques quantifying soil moisture or characterizing a snow pack often require dedicated instrumentation that measures either at point scale or at very large (satellite pixel) scale. Given the heterogeneity of both snow cover and soil moisture in alpine terrain, observations of the spatial distribution of moisture and snow-cover are lacking at spatial scales relevant for alpine hydrometeorology. This paper provides an overview of the challenges and status of the determination of soil moisture and snow properties in alpine environments. Current measurement techniques and newly proposed ones, based on the reception of reflected Global Navigation Satellite Signals (i.e., GNSS Reflectometry or GNSS-R), or the use of laser scanning are reviewed, and the perspectives offered by these new techniques to fill the current gap in the instrumentation level are discussed. Some key enabling technologies OPEN ACCESSRemote Sens. 2013, 5 3517 including the availability of modernized GNSS signals and GNSS array beamforming techniques are also considered and discussed.

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Frequency domain analysis of time domain reflectometry waveforms: 1. Measurement of the complex dielectric permittivity of soils

Cited by 191 publications

References 20 publications

High dielectric insulation coating for time domain reflectometry soil moisture sensor

High dielectric insulation coating for time domain reflectometry soil moisture sensor

Theoretical model of a multisection time domain reflectometry measurement system

Soil Moisture & Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives

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