Time Domain Transmissometry Research Articles

A Method for Measuring the Complex Refractive Index of Low-Volume Materials Using Integrated Terahertz Time-Domain Transmissometry

A Method for Measuring the Complex Refractive Index of Low-Volume Materials Using Integrated Terahertz Time-Domain Transmissometry

High-Sensitivity and Compact Time Domain Soil Moisture Sensor Using Dispersive Phase Shifter for Complex Permittivity Measurement

This article presents a time domain transmissometry soil moisture sensor (TDT-SMS) using a dispersive phase shifter (DPS), consisting of an interdigital capacitor that is loaded with a stacked four-turn complementary spiral resonator (S4-CSR). Soil moisture measurement technique of the proposed sensor is based on the complex permittivity sensing property of a DPS in time domain. Soil relative permittivity which varies with its moisture content is measured by burying the DPS under a soil mass and changing its phase difference while excited with a 114-MHz sine wave (single tone). DPS output phase and magnitude are compared with the reference signal and measured with a phase/loss detector. The proposed sensor exhibits accuracy better than ±1.2% at the highest volumetric water content (VWC = 30%) for sandy-type soil. Precise design guide is developed and simulations are performed to achieve a highly sensitive sensor. The measurement results validate the accuracy of theoretical analysis and design procedure. Owning the advantages of low profile, low power consumption, and high sensitivity makes the proposed TDT-SMS a good candidate for precision farming and internet of things (IoT) systems.

Application of Time Domain Transmissometry to Soil Moisture and Salinity Level Measurements in Reclaimed Agricultural Field Covered in Plastic Sheeting

Application of Time Domain Transmissometry to Soil Moisture and Salinity Level Measurements in Reclaimed Agricultural Field Covered in Plastic Sheeting

Thermometry of a high temperature high speed micro heater.

A high temperature high-speed tungsten micro heater was fabricated and tested for application in phase change switches to indirectly heat and transform phase change material. Time domain transmissometry was used to measure heater temperature transients for given electrical inputs. Finite element modeling results on heater temperature transients show a good consistency between experiments and simulations with 0.2% mismatch in the best case and 13.1% in the worst case. The heater described in this work can reliably reach 1664 K at a rate of 1.67 × 10(10) K/s and quench to room temperature with a thermal RC time constant (time for T to fall by a factor of e) of less than 40 ns.

Accuracy of Two Electromagnetic Soil Water Content Sensors in Saline Soils

Information on the accuracy of commercially available electromagnetic (EM) soil water content sensors in a variety of soil types and over a range of volumetric water content (VWC) and salinity levels is still limited. A laboratory study was conducted to evaluate the accuracy of the Acclima Digital Time Domain Transmissometry (TDT) and the Toro Turf Guard Frequency Domain Reflectometry (FDR) sensors in a loamy sand and a loam soil at soil salinity levels from 2 to 18 dS m−1. Overall linear association between gravimetric and sensor-determined VWC across all salinity levels revealed coefficients of determination between 0.86 and 0.97. In addition to a good linear model fit, a significant quadratic association was also detectable for the TDT sensor in loamy sand at 12 dS m−1 and in loam at 12 and 18 dS m−1. Overall, both sensors reliably measured VWC in both soil types at all salinity levels, however data suggests that different soil types require separate calibration. Moreover, accuracy of the sensor readings can be further improved if differential calibration is applied for different salinity levels. Regression analysis indicated that with increasing salinity, the Turf Guard sensors showed an upward bias (intercept for higher salinities greater than for 3 dS m−1), whereas the TDT sensor exhibited a downward bias (intercept smaller than for low salinitiy levels).

High-Performance and High-Data-Rate Quasi-Coaxial LTCC Vertical Interconnect Transitions for Multichip Modules and System-on-Package Applications

A new design of stripline transition structures and flip-chip interconnects for high-speed digital communication systems implemented in low-temperature cofired ceramic (LTCC) substrates is presented. Simplified fabrication, suitability for LTCC machining, suitability for integration with other components, and connection to integrated stripline or microstrip interconnects for LTCC multichip modules and system on package make this approach well suited for miniaturized, advanced broadband, and highly integrated multichip ceramic modules. The transition provides excellent signal integrity at high-speed digital data rates up to 28 Gbits/s. Full-wave simulations and experimental results demonstrate a cost-effective solution for a wide frequency range from dc to 30 GHz and beyond. Signal integrity and high-speed digital data rate performances are verified through eye diagram and time-domain reflectometry and time-domain transmissometry measurements over a 10-cm long stripline.

Measured and Modeled Soil Moisture Compared with Cosmic‐Ray Neutron Probe Estimates in a Mixed Forest

Soil moisture is a key variable in most environmental processes, and the cosmic-ray neutron probe (CRNP) fills a niche for intermediate-scale soil moisture measurements. In this study, the CRNP estimated soil moisture was compared with a soil moisture measurement network including 108 time domain transmissometry (TDT) probes. We also used a Hydrus-1D numerical model of measured soil moisture at targeted locations by inversely fitting soil hydraulic parameters used to simulate soil moisture in the near surface (0.03 and 0.05 m) during the growing seasons of 2011 and 2012. Both simulated and TDT-measured soil moisture were used in constructing the depth-weighted mean areal soil moisture for comparison with the CRNP estimates. The results showed that near-surface soil moisture estimated by the numerical simulation improved the correlation between the sensor network and the CRNP estimation, especially during rainfall events. The CRNP estimates of soil moisture exhibited a dry bias under relatively wet conditions at the beginning of the snow-free period because of the almost binary spatial distribution of soil moisture. Using a combination of soil moisture measurements and near-surface simulations, the CRNP output was recalibrated to capture the wetter conditions, resulting in a RMSE (0.011 m3/m3) of less than half the original calibration RMSE (0.025 m3/m3). The calibration was validated using CRNP data from the 2013 growing season against independent soil moisture values.

Comparison of Two Soil Water Evaporation Models in a Sandy Soil

Modeling soil water evaporation and soil moisture are valuable for many applications in diverse disciplines. Ritchie and Snyder, presented different models to estimate soil water evaporation (ES) rate. The former also simulates the soil water dynamics at different soil depths. The objectives of this study were to evaluate the potential use of the S2000 model for soils with water content above θDUL in some parts of the profile and to evaluate R2009 ES model and compare its performance with that of S2000. The study was carried out at the University of Florida Indian River Research and Education Center in Fort Pierce, Florida in 2012 and 2013. Eight Time-Domain Transmissometry (TDT) probes were installed in a lysimeter filled with sand and measured hourly soil water content for six months. Three drying cycles (cases) were used for the evaluation of the models. R2009 underestimated the soil water content near the soil surface for Case 1 and 2. While for Case 3, R2009 estimated the near surface soil water content well for the first four days and then it tended to underestimate for the rest of the days. S2000 with the proper parameterization outperformed R2009 which overestimated ES. It was evident that getting the suitable parameterization for S2000 model was not always guaranteed. These finding may only apply for sandy soils similar to the one used in this study. Future studies should be done on different soils and diverse environment before generalization can be made.

Soil Moisture Sensing via Swept Frequency Based Microwave Sensors

There is a need for low-cost, high-accuracy measurement of water content in various materials. This study assesses the performance of a new microwave swept frequency domain instrument (SFI) that has promise to provide a low-cost, high-accuracy alternative to the traditional and more expensive time domain reflectometry (TDR). The technique obtains permittivity measurements of soils in the frequency domain utilizing a through transmission configuration, transmissometry, which provides a frequency domain transmissometry measurement (FDT). The measurement is comparable to time domain transmissometry (TDT) with the added advantage of also being able to separately quantify the real and imaginary portions of the complex permittivity so that the measured bulk permittivity is more accurate that the measurement TDR provides where the apparent permittivity is impacted by the signal loss, which can be significant in heavier soils. The experimental SFI was compared with a high-end 12 GHz TDR/TDT system across a range of soils at varying soil water contents and densities. As propagation delay is the fundamental measurement of interest to the well-established TDR or TDT technique; the first set of tests utilized precision propagation delay lines to test the accuracy of the SFI instrument’s ability to resolve propagation delays across the expected range of delays that a soil probe would present when subjected to the expected range of soil types and soil moisture typical to an agronomic cropping system. The results of the precision-delay line testing suggests the instrument is capable of predicting propagation delays with a RMSE of +/−105 ps across the range of delays ranging from 0 to 12,000 ps with a coefficient of determination of r2 = 0.998. The second phase of tests noted the rich history of TDR for prediction of soil moisture and leveraged this history by utilizing TDT measured with a high-end Hewlett Packard TDR/TDT instrument to directly benchmark the SFI instrument over a range of soil types, at varying levels of moisture. This testing protocol was developed to provide the best possible comparison between SFI to TDT than would otherwise be possible by using soil moisture as the bench mark, due to variations in soil density between soil water content levels which are known to impact the calibration between TDR’s estimate of soil water content from the measured propagation delay which is converted to an apparent permittivity measurement. This experimental decision, to compare propagation delay of TDT to FDT, effectively removes the errors due to variations in packing density from the evaluation and provides a direct comparison between the SFI instrument and the time domain technique of TDT. The tests utilized three soils (a sand, an Acuff loam and an Olton clay-loam) that were packed to varying bulk densities and prepared to provide a range of water contents and electrical conductivities by which to compare the performance of the SFI technology to TDT measurements of propagation delay. For each sample tested, the SFI instrument and the TDT both performed the measurements on the exact same probe, thereby both instruments were measuring the exact same soil/soil-probe response to ensure the most accurate means to compare the SFI instrument to a high-end TDT instrument. Test results provided an estimated instrumental accuracy for the SFI of +/−0.98% of full scale, RMSE basis, for the precision delay lines and +/−1.32% when the SFI was evaluated on loam and clay loam soils, in comparison to TDT as the bench-mark. Results from both experiments provide evidence that the low-cost SFI approach is a viable alternative to conventional TDR/TDT for high accuracy applications.

A Calibrated Time Domain Transmissometry Soil Moisture Sensor Can Be Used for Precise Automated Irrigation of Container-grown Plants

Irrigation control systems that irrigate container-grown plants based on crop water needs can reduce water and fertilizer use and increase the sustainability of ornamental crop production. The use of soil moisture sensors to determine when to irrigate is a viable option. We tested a commercially available irrigation controller (CS3500; Acclima, Meridian, ID), which uses time domain transmissometry (TDT) sensors to measure soil volumetric water content (θ). The objectives of this study were: 1) to test the accuracy of TDT sensors in soilless substrate; 2) to quantify the ability of the Acclima CS3500 irrigation controller to maintain stable θ readings during the production of container-grown begonia (Begonia semperflorens L.) by turning a drip irrigation system on and off as needed; and 3) to study the growth and photosynthetic physiology of begonia at six θ levels. Calibration of the TDT sensors in pots filled with substrate (but without plants) showed that the θ determined by the TDT sensors had a very close relationship (R2 = 0.99) with the gravimetrically determined θ, but the TDT sensors underestimated θ by ≈0.08 m3·m−3. Therefore, a custom calibration of the TDT sensors for the soilless substrate was necessary to get accurate θ data. The irrigation controller was programmed to maintain six θ thresholds, ranging from 0.136 to 0.472 m3·m−3 (based on our own sensor calibration), and was able to maintain θ readings within 0.008 m3·m−3 of the threshold. Theta and Sigma probes were used to collect comparative θ and bulk electrical conductivity (EC) data, respectively. The results showed a strong correlation with TDT sensor measurements of θ (R2 = 0.92) but a moderate relationship for bulk EC (R2 = 0.53). The begonias had similar dry weight at θ levels of 0.348 m3·m−3 and higher, whereas total evapotranspiration increased linearly with the θ threshold. The lowest θ threshold reduced leaf size, net photosynthesis (Pn), and stomatal conductance (gS). Overall, the TDT sensors can provide accurate measurements of θ in soilless substrate but need substrate-specific calibration. The Acclima CS3500 controller, using TDT sensors, was able to maintain stable θ readings throughout a production cycle. These results suggest that this irrigation controller may be suitable for production of greenhouse crops as well as in drought stress research.

Soil water movement modelling in hapllicc luvisols (HMm) and albi hapllic luvisols (HMl) under Slovak climatic conditions

Abstract The aim of the research paper is simulation by the Global Model on the basis of investigation of Slovak Agricultural University (SAU) on two localities (Kolinany and Malanta). The soil moisture was measured by a time domain transmissometry instrument and compared with simulated outputs of the Global Model on Kolinany locality. Measurement of the soil moisture using the gravimetric method was applied on Malanta locality. Sugar beet was grown in Kolinany and, on the other hand, there was no plant on Malanta soil during the experiment. The experiment took three years (2002–2004). Measured and simulated courses of water content were consequently tested by correlation analysis in MS Excel. Result differences between simulated and measured values should reach according to 15 % difference at least 80 % of equality. Correlation between measured and simulated values had a high significance on Kolinany locality (in the range of 0,62–0,90) Equality between measured and simulated values was from 33 % to 75 %...

SOIL WATER MOVEMENT MODELLING IN HAPLLICC LUVISOLS (HMM) AND ALBI HAPLLIC LUVISOLS (HML) UNDER SLOVAK CLIMATIC CONDITIONS

The aim of the research paper is simulation by the Global Model on the basis of investigation of Slovak Agricultural University (SAU) on two localities (Kolínany and Malanta). The soil moisture was measured by a time domain transmissometry instrument and compared with simulated outputs of the Global Model on Kolínany locality. Measurement of the soil moisture using the gravimetric method was applied on Malanta locality. Sugar beet was grown in Kolínany and, on the other hand, there was no plant on Malanta soil during the experiment. The experiment took three years (2002–2004). Measured and simulated courses of water content were consequently tested by correlation analysis in MS Excel. Result differences between simulated and measured values should reach according to 15 % difference at least 80 % of equality. Correlation between measured and simulated values had a high significance on Kolínany locality (in the range of 0,62–0,90) Equality between measured and simulated values was from 33 % to 75 % according to difference of 15 %.

COMPOST INCORPORATION INCREASES PLANT AVAILABLE WATER IN A DRASTICALLY DISTURBED SERPENTINE SOIL

Construction activity typically results in the removal of existing topsoil, exposing unconsolidated parent material that is often difficult to revegetate. In areas with serpentine mineralogy, revegetation is even more difficult because of low nutrient concentrations, heavy metal toxicity, and a low Ca:Mg ratio. Because serpentine-tolerant plants typically display xeric morphology, we hypothesized that water stress was a main factor limiting revegetation on serpentine roadcuts and that compost incorporation would increase plant available water (PAW). Four treatments were evaluated for their ability to increase PAW on a large serpentine roadcut: nontilled (ambient), tilled, and two rates of incorporated compost (270 and 540 Mg/ha or 12 and 24% by volume). Soil water release curves and moisture depletion were measured in situ using time domain transmissometry and soil psychrometers from early spring through the dry summer months. Compost incorporation (24% by volume) resulted in greater than a 2-fold increase in PAW and generated more than 4 times more vegetative biomass compared with the nontilled control. In contrast to the in situ method, by the conventional pressure plate method showed significantly less PAW in the 24% compost treatment compared with the nontilled treatment. In situ measurements of PAW agreed well with biomass data, indicating that for this atypical soil, in situ measurements were more accurate. Compost incorporation into a drastically disturbed serpentine soil is a successful revegetation technique that will increase PAW as well as the ability of the plants to access this water resource through greater root proliferation.

Standardizing Characterization of Electromagnetic Water Content Sensors: Part 2. Evaluation of Seven Sensing Systems

Transmission line‐type electromagnetic (EM) methods for estimating soil volumetric water content (θv) have advanced significantly in recent years, with many sensing systems now available. To estimate θv, EM systems make use of the dependence of soil dielectric permittivity on θv. However, a standard method for characterizing and comparing EM system measurement capability has not been established. Our objective was to evaluate the permittivity measurement ability of seven different EM sensing systems using readily available media. Sensing system outputs were converted to real permittivity (ε′) values and compared with reference ε′ values in lossless and lossy dielectric liquids under four different test conditions: nonrelaxing and nonconducting (NR‐NC), relaxing and nonconducting (R‐NC), nonrelaxing and electrically conducting (NR‐C), and temperature variation in NR‐NC. The higher frequency broadband sensing systems, consisting of two time domain reflectometry (TDR) systems and one time domain transmissometry (TDT) system, deviated from a network analyzer by less than ±2.94 ε′ units across a ε′ range of 12.7 to 78.5 in NR‐NC media. Two lower frequency impedance sensing systems deviated from the network analyzer by less than ±3.94 ε′ units across a ε′ range of 12.7 to 36.5 in the same media. Measurement of ε′ using higher frequency broadband sensing systems was impacted more by bulk electrical conductivity (σb) and temperature (T) than by dielectric relaxation. Imaginary permittivity values (due only to relaxation, ε″rel) of up to 14.5 in R‐NC media resulted in ε′ errors of ±0.511, whereas σb values ranging from 0 to 2 dS m−1 in NR‐C media resulted in ε′ errors of ±2.69 and T values ranging from 5 to 40°C resulted in ε′ errors of ±4.89. Determination of ε′ using lower frequency sensing systems—including one transmission line oscillator, two impedance probes, and one capacitance probe—was impacted more by σb than by T and ε″rel For the lower frequency sensors (and the same ranges of σb, T, and εrel), σb resulted in ε′ errors of ±111, T resulted in ε′ errors of ±6.59, and ε″rel resulted in ε′ errors of ±3.28. The effects of ε″rel, σb, and T on permittivity measurement accuracy is to a large extent dependent on measurement frequency, with higher frequency broadband sensing systems generally yielding better measurements.

Determination of water content and salinity from a producing oil well using CPW probe and eigendecomposition

The main aim of this study is to demonstrate the ability to determine the water content and salinity of a producing oil well by analyzing captured time domain transmissometry (TDT) pulse signals by the newly developed coplanar waveguide (CPW) probe using eigendecomposition technique. The proposed technique characterizes the captured signatures by a number of eigenvalues calculated by autoregressive modeling and singular value decomposition methods. To demonstrate the proposed method of analysis, crude oil samples obtained from Al Bab oil reservoir, Abu Dhabi Emirate, UAE, were used. The physicochemical properties were first determined as functions of formation water content and salinity and then samples were prepared for their use with the CPW probe for signal detection in the TDT mode of operation. Transmitted signals were analyzed using eigendecomposition technique and the most significant eigenvalues were identified based on their power. Multivariate statistical analysis was then performed and the regression analysis resulted in a system of linear equations that best described the system. Actual and predicted results are in agreement, indicating a good performance and versatility of the developed system for wide range of formation water content and salinities in the tested crude oil.

Noncontacting determination of moisture content in bulk materials using sub-nanosecond UWB pulses

This paper presents a new approach of noncontacting moisture determination in bulk materials utilizing time-domain transmissometry. The described method is independent of the mass per area of the material under test and does not suffer from measurement ambiguities, which are well known from frequency-domain methods. Ultra-wideband quasi-Gaussian monocycle pulses are applied with a cycle width of approximately 400 ps. The measurement signal is transmitted through the material over free space using double-ridged horn antennas. The received signal is acquired in the time domain and analyzed with different methods of data processing. The results obtained with multiple linear regression, principal component analysis, and artificial neural networks are compared with each other. Furthermore, a possible hardware implementation for a dedicated time-domain transmissometer is proposed based on a earlier developed time-domain reflectometer for the determination of food quality.

Irrigation automation with heterogeneous vegetation: the case of the Padova botanical garden

An automated control system was set up in the Padova Botanical Garden integrating the information on the soil water status supplied by time domain transmissometry (TDT) sensors with the aid of an irrigation microcomputer. The automatic system consisted of four parts: (a) an irrigation network and electronic control unit (microcomputer); (b) a monitoring system of the soil moisture and water table depth; (c) a management software; and (d) a datalogger connecting sensors to the irrigation microcomputer. Sensors were chosen so that they could be remotely connected through cabling over more than 100 m, guaranteeing adequate accuracy and high reliability over time. To take into account the heterogeneity of plant cover, the site was divided into six irrigation macro-sectors managed separately by the automated system. These macro-sectors were selected by classifying the area on the basis of water requirements, cover type and evapotranspiration demand. The software allowed different irrigation criteria to be defined, considering the values supplied by the moisture sensors singly or on average. In the first year, the automation worked adequately, allowing the irrigation to be managed on the basis of defined thresholds. The irrigation criterion used in the first year for the automated management within macro-sectors, although allowing a favourable water potential to be maintained on average, does not appear to have adequately evaluated the variability of behaviour of the different plants.