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Coal mining has an important influence on the soil water content in the vadose zone. In this study, during April, August and October 2015 and June 2016, ground-penetrating radar was used to detect the soil water content of the shallow sand layer (

The most important biotic stress factor impacting tomato crop biophysical, biochemical, physiological, and morphological features is water stress. A pot experiment was undertaken in a greenhouse to study the drought responsiveness of tomato (Solanum lycopersicum) yield and quality indices in sandy loam and silty loam soils. For both sandy loam and silty loam soils, the water supply levels were 70–100% FC, 60–70% FC, 50–60% FC, and 40–50% FC of ETo (crop evapotranspiration) from the vegetative stage to the fruit ripening stage, calculated using the Hargreaves–Samani (HS) model compared to the time-domain reflectometer (TDR) values calibrated using volumetric water content (VWC). The experiment was conducted as a 2 × 4 factorial experiment, arranged in a completely randomized block design, with four treatments replicated four times. In this study, we examined how sandy loam and silty loam soils at different % FC affect the total marketable yield and quality components of tomatoes, concentrating on total soluble solids (Brix), fruit firmness, dry fruit mass, pH, titratable acid (TA), ascorbic acid (Vit. C), and carotenoid composition. Lycopene and β-Carotene were estimated using the UV spectroscopy method, with absorption spectra bands centered at 451 nm, 472 nm, 485 nm, and 502 nm. The results revealed that even though there were some limitations, TDR-based soil moisture content values had a strong positive correlation with HS-based evapotranspiration, with R2 = 0.8, indicating an improvement whereby TDR can solely be used to estimate soil water content. Tomato plants subjected to 40–50% FC (ETo) water stress in both sandy loam and silty loam soils recorded the highest total soluble solids, titratable acidity, ascorbic acid content, and β-carotene content at an absorption peak of 482 nm, and lycopene content at an absorption peak of 472 nm, with lower fruit firmness, fruit juice content, and fruit juice pH, and a reduced marketable yield. Similarly, tomato plants subjected to 60–70% FC throughout the growing season achieved good fruit firmness, percent juice content, total soluble solids, titratable acidity, ascorbic acid content, and chlorophyll content (SPAD), with minimum fruit juice pH and high marketable yield in both soil textural types. It is concluded that subjecting tomato plants to 60–70% FC (ETo) has a constructive impact on the marketable yield quality indices of tomatoes.

Phase-demodulated phase-sensitive time domain reflectometer (Φ-OTDR) has attracted much attention because of its linear relationship between the phase variation and the amplitude of the vibration. However, it suffers from limited signal-to-noise ratio (SNR) and signal fading, due to the inherent low Rayleigh scattering coefficient and randomly spatial non-uniform distribution of the refractive index. Here, a Φ-OTDR system based on wavelength diversity is demonstrated, which can enhance the SNR and reduce signal fading simultaneously by using differential vector aggregation method. A theoretical model is built, and the linear relationship between SNR improvement and diversity scale is analyzed. The verification experiment is conducted, and in the further experiments, the frequency and wavelength diversity technology are cascaded to achieve a diversity scale of 20. After differential vector aggregation method, the external disturbance signal is well reconstructed and the noise floor is reduced by 13.4 dB, which is basically consistent with the theoretical analysis.

In this paper, we propose a dual wavelength scheme for the detection of liquids based on optically absorbing (Co2+-doped) optical fibers. The proposed configuration makes use of a Coherent-Optical Time Domain Reflectometer (C-OTDR) operating with standard fibers at 850 nm. Besides vibration measurements over all the sensing fiber, the proposed scheme performs liquid detection in short sections of Co2+-doped fibers, heated by a modulated optical pump at 1550 nm. We demonstrate that the proposed sensor detects the liquids surrounding the doped fiber, such as water or acetone.

An experimental set-up was constructed based on an ytterbium pulsed laser with a passive holmium fiber shutter, which provides time-domain reflectometry research the length of active fiber samples after drawing and during storage. The possibility of studying non-uniformities in the fiber and quantifying the attenuation coefficient of the optical signal at the source wavelength is discussed. The results indicate the possibility of conducting studies of this type, as well as the potential development of reflectometers for the needs of laboratories of enterprises that produce active optical fibers commercially.

У статті запропоновано багатокритеріальну модель якісної оцінки та вибору сучасних імпульсних рефлектометрів. Метою дослідження є прискорення процедури визначення найкращої моделі рефлектометра відповідної фірми за рахунок створення критеріального рівняння на базі моделювання та візуалізації багатопараметричних критеріїв якості: розроблено реляційну модель множини сучасних імпульсних рефлектометрів зі структурованими даними техніко-економічних показників; складено умовні критерії розмірностей за визначальними величинами на основі теорії розмірностей, побудовано багатокритеріальну модель якісної оцінки сучасних імпульсних рефлектометрів у безрозмірних координатах, проведено порівняльний аналіз за параметрами для визначення найкращої моделі рефлектометра визначеної фірми. Розроблена модель дає можливість пришвидшити процес проектування і вибрати шлях по вдосконаленню та забезпеченню високої якості пристроїв цього типу. A multicriteria model of qualitative assessment and selection of modern time-domain reflectometers is proposed in the article. The purpose of this study is to accelerate the procedure of determining the best model of the reflectometer from the appropriate company by creating a criterial equation based on modeling and visualization of multi-parameter quality criteria. A relational model of a set of modern time-domain reflectometers with structured data of technical and economic indicators has been developed. Conditional dimensional criteria for determining values based on dimension theory have been compiled. A multicriteria model of qualitative assessment of modern timedomain reflectometers in dimensionless coordinates has been constructed. A comparative analysis to determine the best model of the reflectometer of a certain company by parameters has been performed. To solve this problem, a set of modern time-domain reflectometers with structured data of technical and economic parameters in the form of a relational model is defined. It is proposed to use dimensional theory, physical modeling and to create conditional quality criteria based on the heuristic method. Comparative analysis shows that Megger company is the best in terms of dimensional criteria. The histogram compares technical and economic indicators of time-domain reflectometers of this company. As can be seen from the comparison of technical and economic indicators of Megger time-domain reflectometers, Megger Teleflex VX model, which has the best range and accuracy is the best one. The developed model allows to accelerate the design process and select the way to improve and ensure high quality for devices of this type

A viable wide-band circuit model of parallel corrugated differential transmission line is established. By solving for the even- and odd-modes in this structured differential transmission line, the equivalent capacitance, inductance, resistance, and conductance per unit length are calculated, then the characteristic impedances of differential and common signals are obtained. The ${S}$ -parameters obtained from the equivalent circuit model agree well with the full-wave simulation results with a deviation of only about 0.036 dB in the frequency range of 10 GHz. Experimentally, the characteristic impedances are measured for the differential and common signals using a time domain reflectometer (TDR). The deviation between the experimental and theoretical results was less than 1.05%. Based on the equivalent circuit model, it is feasible to implement this type of structured differential line directly into real circuits.

Sentinel-1 and Landsat-8 data were used to retrieve soil moisture from top soil surface (0–5 cm depth) at agricultural land (area under wheat crop). After pre-processing of satellite data and removal of vegetation influence (σ°veg) using Water Cloud Model (WCM), total backscattering coefficient (σ°total) and Normalized Difference Vegetation Index (NDVI) were used to simulate backscattering from soil (σ°soil). Modified Dubois Model (MDM) and Topp's Model were used to retrieve soil moisture using ε. Further, modelled soil moisture was evaluated using in situ soil moisture measurements and a Time Domain Reflectometer during Sentinel-1 overpass (24 January, 25 February and 13 March 2018). Statistical tests showed that an integrated approach has potential to improve soil moisture estimates over the vegetated/cropped area for agricultural and hydrological studies.

A transparent interconnects on a 16 layer PCB stack-up with a 100 Ω differential impedance with interconnects is proposed in this paper. To minimize the differential crosstalk, a differential spacing is maintained between interconnects. The transmitter and receiver are demonstrated as Input Buffer Information Specification (IBIS) models. An IBIS model describes the V-I characteristics information about the particular buffer. To provide better channel performance, the interconnect Via structures are optimized in this paper. To observe the channel performance in the frequency domain, S-parameter analysis is performed. To view BER plots, eye diagram and bathtub curve analysis is implemented. To observe the impedance with respect to the propagation delay of the channel, Time Domain Reflectometer (TDR) analysis is performed. Debugging and impedance discontinuity correction are performed using TDR analysis. ADS 9 (Advanced Design System) simulation software is used in this paper.

This study investigates variations in the velocity and sensitivity of electromagnetic waves in transmission lines configured in defective model piles for the detection of necking defects containing soil. Experiments are performed with model piles containing defects filled with different materials, such as air, sands, and clay. Five different types of transmission lines are configured in model piles. The electromagnetic waves are generated and detected using a time domain reflectometer. The velocity of electromagnetic waves is highest when the defect is filled with air, and it decreases with an increase in the water content. The velocity is lowest when the defect is filled with clay. The sensitivity of transmission lines for detecting defects decreases with an increase in soil water contents. The transmission line with a single electrical wire and epoxy-coated rebar exhibits the highest sensitivity, followed by that with three and two parallel electrical wires. Transmission lines with a single electrical wire and uncoated rebar and those with two parallel electrical wires wrapped with a sheath exhibit poor sensitivity when the defect is filled with clay. This study demonstrates that electromagnetic waves can be effective tools for detecting necking defects with wet and conductive soils in bored piles.

The paper considers simulation model of a linear radio-frequency path of overhead power line implemented in the PSCAD software environment, which allows studying the propagation of location signals along the overhead power line conductors in 6–10 kV distribution circuits in terms of single phase to earth faults occurrence. Model and corresponding time domain reflectometer trace recorded in laboratory and field conditions for overhead power lines when simulating various types of single phase to earth faults are compared. The methods of location based determination of the single phase to earth faults distance and location on the conductors are given. The results of model and experimental studies in cases of single phase to earth faults show high convergence and performance of model and experimental time domain reflectometer traces of the 6–10 kV line, which indicates the representativeness of the developed model and the possibility of its use in location-based monitoring of 6–10 kV overhead lines.

The stability of tunnels and rock slopes is adversely affected by defects in rock bolts. This study investigates the suitability of the smart sensing method using electromagnetic waves for inspecting defects in rock bolts. Experiments were performed with one fully grouted and eight defective rock bolts, out of which five have non-grouted parts at the ends with different non-grouted ratios, and three have different types of voids. Electromagnetic waves were generated and detected using a time domain reflectometer by configuring two-conductor transmission lines in the rock bolts. Results show that electromagnetic waves are reflected both at defects and ends of rock bolts. The electromagnetic wave velocity increases with an increase in the non-grouted ratio and decreases when rock bolts are embedded in a concrete block simulating rock mass. The estimated locations of defects found by electromagnetic waves are in good agreement with actual defect locations. This study demonstrates that smart sensing using electromagnetic waves is an effective method for inspecting and determining defect locations and the non-grouted ratio of rock bolts.

A multicriteria model of qualitative assessment and selection of modern time-domain reflectometers is proposed in the article. The purpose of this study is to accelerate the procedure of determining the best model of the reflectometer from the appropriate company by creating a criterial equation based on modeling and visualization of multi-parameter quality criteria. A relational model of a set of modern time-domain reflectometers with structured data of technical and economic indicators has been developed. Conditional dimensional criteria for determining values based on dimension theory have been compiled. A multicriteria model of qualitative assessment of modern time-domain reflectometers in dimensionless coordinates has been constructed. A comparative analysis to determine the best model of the reflectometer of a certain company by parameters has been performed. To solve this problem, a set of modern time-domain reflectometers with structured data of technical and economic parameters in the form of a relational model is defined. It is proposed to use dimensional theory, physical modeling and to create conditional quality criteria based on the heuristic method. Comparative analysis shows that Megger company is the best in terms of dimensional criteria. The histogram compares technical and economic indicators of time-domain reflectometers of this company. As can be seen from the comparison of technical and economic indicators of Megger time-domain reflectometers, Megger Teleflex VX model, which has the best range and accuracy is the best one. The developed model allows to accelerate the design process and select the way to improve and ensure high quality for devices of this type., У статті запропоновано багатокритеріальну модель якісної оцінки та вибору сучасних імпульсних рефлектометрів. Метою дослідження є прискорення процедури визначення найкращої моделі рефлектометра відповідної фірми за рахунок створення критеріального рівняння на базі моделювання та візуалізації багатопараметричних критеріїв якості: розроблено реляційну модель множини сучасних імпульсних рефлектометрів зі структурованими даними техніко-економічних показників; складено умовні критерії розмірностей за визначальними величинами на основі теорії розмірностей, побудовано багатокритеріальну модель якісної оцінки сучасних імпульсних рефлектометрів у безрозмірних координатах, проведено порівняльний аналіз за параметрами для визначення найкращої моделі рефлектометра визначеної фірми. Розроблена модель дає можливість пришвидшити процес проектування і вибрати шлях по вдосконаленню та забезпеченню високої якості пристроїв цього типу.

This paper presents a non-destructive method for detecting necking defects in bored piles using electromagnetic waves. Small-scale laboratory experiments are conducted with a defective model pile with diameter of 0.6 m and length of 1.0 m. Four artificial necking defects are introduced on three different sides of the model pile. One necking defect is introduced at the upper position on one side of the model pile, another one is introduced at the lower position on other side of the model pile, and the other two are introduced at both the upper and lower positions on the same side of the model pile. Electrical wires are installed alongside the main rebars of a reinforcement cage to configure a two-conductor transmission line. Electromagnetic waves are generated and detected using a time domain reflectometer. The experimental results indicate clear detection of the reflected electromagnetic waves at the necking defects and pile end. In addition, the calculated defect locations are similar to the actual locations. This study demonstrates that electromagnetic waves can be effective in detecting necking defects at various positions in bored piles.

Polarization diversity reception is a widely used method to suppress polarization fading of Φ -optical time domain reflectometer ( Φ -OTDR). However, the traditional polarization diversity reception method with multichannel point-to-point signal aggregation causes the discontinuity of the aggregated signal, which affects the subsequent application. In order to decrease the discontinuity of the aggregation signal, an area-to-area signal aggregation method with a Rayleigh gray-scale pattern is proposed. First, the Rayleigh pattern is simulated to verify the large-scale continuity of fading areas. Then, an image-processing method by Rayleigh gray-scale pattern is carried out for the automatic judgment of large-scale fading areas, which includes the operations of normalization, graying, comparison of amplitude threshold using the Otsu algorithm, erosion, and dilation. The experimental results indicate that multichannel area-to-area signal aggregation can reduce the average fading ratio from 6.58% to 2.10% and also realize the signal demodulation with an SNR of 15.83 dB of positioning curve. This aggregation method provides an effective scheme for the polarization-fading suppression for Φ -OTDR.

An ultra-wide-band radar module sensor for soil moisture monitoring field experiment is investigated in this paper. For this type of mission critical sensor, it is applied to collect the reflected signals from subsurface of bare soil and sand with different volumetric water contents (VWCs) data (which are calibrated by a time domain reflectometer). This problem is formulated as a mapping from the raw data to the physical parameter. The fuzzy logic algorithm is employed to track the trend of the time series data and after the forecasting becomes stable, the parameters of membership functions in the final iteration are extracted as templates and the VWC values are computed based on a recognition fashion. Two type of fuzzy logic systems (FLSs), namely, type-1 FLS and interval type-2 FLS are employed and compared under the root-mean-square-error. Finally, the accuracy of the soil moisture retrieval is also compared under the mean absolute deviation and the root mean square difference, which demonstrates the effectiveness of the algorithm.

A new type of dual-line multiprobe reflectometer, featuring an ultra-wideband operational bandwidth, is proposed. The presented reflectometer is composed of two parallel transmission lines along which weakly coupled probes are arranged. By utilization of two separate transmission lines, the minimum distance between two consecutive probes can be smaller than the length of a single probe, which allows for a highly nonuniform probes’ arrangement required to ensure ultra-wideband operation. Moreover, an efficient algorithm for the probes’ arrangement ensuring maximization of reflectometer’s bandwidth is proposed. The proposed concept has been validated by the design of an ultra-wideband dual-line multiprobe reflectometer having six probes and operating frequency range over 0.1–12 GHz. The obtained results are in a very good agreement with the reference values measured using a commercial VNA.

Time domain measurement techniques that determine the even- and odd-mode characteristic impedances and far end terminal resistances are presented for a coupled strip line network. It is not necessary to change the setup conditions at the near end terminals. Instead, the first and second impulse response components of reflection and transmission coefficients are used. Four combinations of the impulse components are discussed for characterization. In experiments, the use of a time domain reflectometer or a network analyzer equipped with software of an inverse fast Fourier transform (IFFT) is premised.

Commercial soil moisture measurement devais based on time-domain reflectometry (TDR) are considerably expensive for daily practice by Indonesian farmer. In this paper, we present development of a low cost microcontroller based electronics soil moisture measurement system using TDR. We utilize the equivalent time sampling technique to enhance range of measurement frequency while the sigma delta modulation is used in implementation. Our sensor system is based on M-4 ARM Cortex microcontroller, working on a 100- KHz signal and virtual sampling resolution within 0.11 ns. The developed sensor system was able to reconstruct a typical TDR wave with reflection within several nanoseconds.

The overview of different types of reflectometers is given. The theoretical calculation of factors, such as instability of internal reference clocks and resolution of time interval measurement device, influencing on resolution and uncertainty of signal delay (which can be calculated into length) is given. One of the ways to decrease uncertainty type A of distance measurements is suggested scheme of pulse reflectometer with multistop event timer. Due to ability of measurement averaging it is possible to reduce resolution less then 0.1 mm. In the work principle of operation of the proposed reflectometer and functional scheme are given. The impact of such factors as chromatic and polarization mode dispersion, timer trigger error, temperature fluctuations are considered. The requirements to laser module due to dispersion characteristics of measured fiber are given. The temperature variation affects mostly on signal delay in photodetector and other electronics. It also changes the delay of optical pulse in fiber coil, which is used for dead zone riddance. The results of theoretical error limits calculations for such reflectometers are presented. The results of experimental studies of reflectometer are presented. It is shown that the proposed scheme of the optical time domain reflectometer and technical solutions make possible the signal propagation delays measurements with an resolution better than 5 ps and combined uncertainty less than 100 ps.

Although soil nails have been widely used for stabilizing slopes, they are often only partially grouted. Thus, grouted ratio of soil nails should be evaluated to prevent landslides. The purpose of this study was to investigate the suitability of a non-destructive method using electromagnetic waves for evaluating grouted ratio of soil nails. Experimental studies were performed with steel bars, partially grouted steel bars, and fully grouted steel bars in air. Partially and fully grouted steel bars were also installed in soils to simulate soil nails installed on slopes. Electromagnetic waves were generated and received using a time domain reflectometer by configuring a two-conductor transmission line formed by two parallel steel bars or two parallel grouted steel bars. Results of experiments showed that the respective round-trip travel time of electromagnetic waves increased with increasing length of the steel bar, grouted steel bar in air, and grouted steel bar in soils. The velocity of electromagnetic waves was the greatest in steel bars but the lowest in grouted steel bars in soils. In addition, the velocity of the electromagnetic waves decreased with increasing grouted ratio. This study suggests that electromagnetic waves might be useful for evaluating grouted ratios of soil nails to stabilize slopes.

It is necessary to reduce the crosstalk noise in high-speed signaling channels. In the channel routing area, the tabbed routing pattern is used to mitigate far-end crosstalk (FEXT), and the electrical length is controlled with a time domain reflectometer (TDR) and time domain transmission (TDT). However, unlike traditional channels having uniform width and space, the width and space of tabbed routing changes by segment, and the capacitance and inductance values of tabbed routing also change. In this paper, we propose a tabbed routing equivalent circuit modeling method using the segmentation approach. The proposed model was verified using 3D EM simulation and measurement results in the frequency domain. Based on the calculated inductance and capacitance parameters, we analyzed the insertion loss, FEXT, and self-impedance in the frequency domain, and TDT and FEXT in the time domain, by comparing the values of these metrics with and without tabbed routing. Using the proposed tabbed routing model, we analyzed tabbed routing with variations of design parameters based on self- and mutual-capacitance and inductance.

We demonstrate a distributed optical fiber sensing system based on the Michelson interferometer of the phase sensitive optical time domain reflectometer (φ-OTDR) for acoustic measurement. Phase, amplitude, frequency response, and location information can be directly obtained at the same time by using the passive 3×3 coupler demodulation. We also set an experiment and successfully restore the acoustic information. Meanwhile, our system has preliminary realized acoustic-phase sensitivity around −150 dB (re rad/μPa) in the experiment.

Soil moisture content is one of the most important parameters of hydrological studies. Cosmic-ray neutron sensing is a promising proximal soil moisture sensing technique at intermediate scale and high temporal resolution. In this study, we validate satellite soil moisture products for the period of March 2015 and December 2018 by using several existing Cosmic Ray Neutron Probe (CRNP) stations of the COSMOS database and a CRNP station that was installed in the south part of Turkey in October 2016. Soil moisture values, which were inferred from the CRNP station in Turkey, are also validated using a time domain reflectometer (TDR) installed at the same location and soil water content values obtained from a land surface model (Noah LSM) at various depths (0.1 m, 0.3 m, 0.6 m and 1.0 m). The CRNP has a very good correlation with TDR where both measurements show consistent changes in soil moisture due to storm events. Satellite soil moisture products obtained from the Soil Moisture and Ocean Salinity (SMOS), the METOP-A/B Advanced Scatterometer (ASCAT), Soil Moisture Active Passive (SMAP), Advanced Microwave Scanning Radiometer 2 (AMSR2), Climate Change Initiative (CCI) and a global land surface model Global Land Data Assimilation System (GLDAS) are compared with the soil moisture values obtained from CRNP stations. Coefficient of determination ( r 2 ) and unbiased root mean square error (ubRMSE) are used as the statistical measures. Triple Collocation (TC) was also performed by considering soil moisture values obtained from different soil moisture products and the CRNPs. The validation results are mainly influenced by the location of the sensor and the soil moisture retrieval algorithm of satellite products. The SMAP surface product produces the highest correlations and lowest errors especially in semi-arid areas whereas the ASCAT product provides better results in vegetated areas. Both global and local land surface models&rsquo, outputs are highly compatible with the CRNP soil moisture values.

As data rates continue to rise, data protocols allow engineers the bandwidth and speed necessary to utilize an ever increasing video resolution and quality. The Mobile Industry Processor Interface (MIPI) D-PHY CSI-2 protocol is one such solution. The MIPI standards utilizes High Speed (HS) and Low Power modes. These modes occupy the same data lines, making oscilloscope measurements difficult to obtain because the modes are constantly switching. In addition, the amount of data sent, during HS mode, changes with each packet. Real time oscilloscopes can recognize the HS mode data and wait for single triggered measurements to create a real time eye diagram. This process is time consuming and if the PCB is not designed for signal integrity testing, the measurements involve holding a differential probe steady on the DUT, introducing human error. In this paper, we propose to use Time Domain Reflection (TDR) measurements which can be easily made on any board as they do not require capturing live data. Using differential probes, TDR measurements also capture waveforms for each data lane and obtain an eye diagram. Results show a good correlation between real time scope and TDR eye diagrams. Also, TDR software allows S-parameters to be obtained.

A Time Domain Reflectometer (TDR) with rise time of 5ns is developed using a Digital Storage Oscilloscope (DSO) of 200MHz having data storing capacity of 2000 data points for a single waveform. This TDR is used to calculate the Velocity of Propagation (VOP) in a transmission line and if any impedance mismatches due to addition of any other transmission line. The proposed paper explains the system accuracy by calculating the VOP of different transmission lines and the distance of impedance mismatch from the place where the new transmission line is added.

A six-port reflectometer providing an improved power distribution is proposed. The developed six-port network allows for a significant enhancement of the measurement accuracy without increasing the complexity of the reflectometer’s network. The proposed six-port has been theoretically analyzed, designed in a stripline technique with the use of single-section coupled-line directional couplers, and fabricated. For the experimental verification, the developed six-port has been utilized in reflection coefficient measurements in a wide frequency range, 2.5–3.5 GHz. The obtained results are very close to the reference values measured using a vector network analyzer. Furthermore, the same measurements have been performed utilizing the classical six-port reflectometer operating within the same frequency range. The comparison clearly shows that the proposed six-port reflectometer provides a significantly higher measurement accuracy with respect to the classical solutions.

The paper develops a statistical model for the signals received in phase-sensitive optical time domain reflectometry (OTDR) probed by highly coherent sources. The backscattering process is modelled by a set of discrete scatterers with properly chosen parameters. Explicit equations for calculating the amplitude and the phase of the backscattered signal are obtained. The developed model predicts spectral and autocorrelation characteristics of the amplitude signals that are validated by experimental results. Characteristics of the phase signals, practicable for studying the sensing applications of the OTDR system, are presented and studied as well, demonstrating good correspondence with experiment. A more detailed modelling of distributed vibration sensing systems and their response to disturbances along an optical fiber will be possible as an extension of the developed formalism.

We demonstrate the design and characterization of a distributed optical fiber sensing system based on Michelson interferometer of the phase sensitive optical time domain reflectometer (φ-OTDR) for acoustic measurement. Phase, amplitude, frequency response and location information can be directly obtained at the same time by using the passive 3×3 coupler demodulation. In order to simulate sound profiles of seismic or hydroacoustic imaging, experiments on detection of multiple piezoelectric transducers (PZT) are carried out. The result shows that our system can well demodulate different acoustic sources with different intensities.

We report a novel experimental setup to perform distributed characterization in intensity and phase of the nonlinear stage of modulation instability by means of a non-invasive experimental setup : a heterodyne time domain reflectometer.

Time domain reflectometer (TDR) has gained popularity among researchers in determination of soil water content due to simplicity and fast. It is a non-destructive tool to carry-out test upon soil. Rapid increment of soil water content and subsequently results in sudden reduction of soil shear strength, will cause detrimental effect to the geotechnical structure. TDR has the ability to measure soil water content on the spot without testing the moisture content of physical sample in laboratory. In this study, TDR uses two parallel probes to measure the resistance of a soil media with pre-determined volumetric water content. The results in previous study have shown that good accuracy in determination of moisture content using TDR especially for sandy and loamy soils, however in clayey soil, are yet to be confirmed. Several factors are identified to significantly affect the accuracy in measurements using clayey soils especially when the moisture content increase. The findings on determination of soil water content for Malaysian clay soil using TDR are summarized in this paper. Similar behavior were observed with past study in which the accuracy in measurement using TDR were reduced as the amount of soil water content increase of more than 30%.

This paper presents a method of using TDR (Time Domain Reflectometry) in a passive way to detect and determine the location of irregularities on a transmission line. pTDR (Passive Time Domain Reflectometer) technology [1] was implemented on an FPGA (Field Programmable Gate Array). By using PLL (Phase locked loop) phase shifters and high speed digital counters [2] the system was able to accurately measure the return time of the reflections (created by the irregularities). This enabled the system to accurately determine the location of the irregularities on the transmission line.

This paper demonstrates the feasibility of detecting brief intermittent arcs on wired networks and characterizing them by mathematical modelization. We develop models of reflections generated by arc defects in transmission lines excited by specific test signals, using time-domain reflectometry. Arc fault causes a local modification of the propagation characteristics of the cable. The MCTDR (Multi-carrier Time Domain reflectometry) reflectogram shows the arc as peaks due to impedance change. The location and arc characteristics are automatically calculated and displayed by a computer device. This study provides an accurate assessment of the severity of the arc fault, as the peak amplitude depends heavily on the arc fault impedance, but also on other impedance changes on the cable.

The paper describes Noise waveform reflectometer of a new type, which uses wideband random signals and spectral interferometry method for fiber optical network diagnostics. Also correlation based reflectometer was submitted and investigated. These reflectometers have no so-called “dead zone” and are used for metrological support of fiber-optic communication lines (FOCL).

This paper presents the characterization and operation of an alternative device, which is known as multi-port reflectometer to measure the reflection coefficient of any device under test (DUT). Its configuration is formed by two power dividers (D) and four couplers (Q). The characterization is evaluated through the centres of power circles that also known as q-points. Its operation in the reflection coefficient measurement is tested by using three DUTs. The reflectometer’s good performance and wideband operation are proven between the frequency band of 1 and 6 GHz via the practical hardware measurement in the laboratory.

This paper presents a single-chip 0.01–26 GHz reflectometer for two-port vector network analyzers (VNA). The reflectometer consists of a bridge coupler integrated together with two wideband heterodyne receivers. For wideband operation, a resistive bridge coupler is used with a directivity of 33 dB up to 26 GHz. Also, a high-linearity receiver channel is designed so as to accommodate 10 dBm of RF input power to the reflectometer. The SiGe chip is 1.8 mm2 and consumes 640 mW from a 3.3 V supply. The dynamic range of the reflectometer chip is 127±2 dB at 0.01–26 GHz with an IF resolution bandwidth (RBW) of 10 Hz. The chip is placed on a printed circuit board (PCB), and RF, LO and DC bias are connecterized. Measurements of several device-under-test units (DUTs) with a two-port 0.01–26 GHz VNA composed of two reflectometer chips shows excellent agreement with a commercial VNA, with a magnitude and phase difference of 21 as well as minimal magnitude and phase difference compared to state-of-the-art VNA measurements.

25th International conference on Optical Fiber Sensors, , 24/04/2017-28/04/2017, Jeju, Corea del Sur., We review our recent work on chirped-pulse phase-sensitive optical time-domain reflectometry along optical fibers and its application in the measurement of true nanostrain variations in the kHz frequency range over km-long fibers. We also show how this technique can be used to perform distributed photothermal measurements of gas presence in suitable microstructured fibers., European Commission, Ministerio de Economía y Competitividad

We demonstrate a distributed localization of an impact source in the composite cylinder using a home-made phase-sensitive optical time domain reflectometer (Φ-OTDR). The system shows the advantages of simple configuration using semiconductor optical amplifier to improve the spectral response of the pump pulses, high spatial resolution and high signal-to-noise ratio (SNR). With a spatial resolution of 10 m, the SNR could be obtained as high as 6.5 dB. A composite cylinder is longitudinally divided in multiple sections of equal lengths by bending the sensing fibers around it at different locations, and the section of a source impact is localized using the time-delay of the signal detected by the sensing fibers.

A compact and low cost portable vector reflectometer is designed for a reliable measurement of reflection coefficient, S11. This reflectometer focuses on return loss measurement of frequency ranges from 450 MHz to 550 MHz. The detection of magnitude and phase is based on the utilization of surface mount Analog Devices AD8302 gain/phase detector. The data acquisition is controlled by using Arduino-Nano 3.0 microcontroller, with the use of two analog to digital converter (ADC) and a digital to analog converter (DAC). One port (Open, short and matched load) calibration technique is used to eliminate systematic errors prior to data acquisition. The evaluation of the reflectometer is done by comparing the result of the measurement to that of vector network analyzer.

Soil water content (SWC) is a critical attribute in precision irrigation. Direct measurements are costly and relative sparse, so there is interest in methods to predict SWC at unsampled sites from sampled data. The precision of such predictions can be improved, if covariates are incorporated into the predictor. To do that, two efficient ways are: (1) linear mixed effect model (LME), in which the spatial process is obtained by splitting the total variability in a systematic term or mean effect, a spatially correlated component and a random noise, and (2) kriging with external drift (KED), a nonstationary geostatistical technique, assuming covariates to have a linear effect on target variable. Geoelectric sensors provide noninvasive information on soil. Their outputs are quite sensitive to SWC; therefore, they can be used as covariates in SWC predictor. The objective of this work was to compare LME and KED, based on geophysical sensing, to estimate shallow SWC. The surveys were conducted in a south-eastern Italy field, using GPR at two frequencies, 600 and 1,600 MHz, and EMI. Volumetric soil water contents were measured with a Time Domain Reflectometer at 96 locations. Three LMEs, using three correlation functions (spherical, exponential, and Gaussian), were used and compared with KED using a set of cross-validation criteria. The mixed models showed a quite similar behavior even if exponential model outperformed the other two. The covariates used in the mixed models and in KED predictor were different and the results of cross-validation showed a slight out-performance of KED.

By a modeling technique of equivalent lumped circuit for high-speed interconnections, an innovative method is proposed to predict the physical intrinsic eye diagram. Such a technique is based on the measured impedance profile results of time-domain reflectometry, which includes the electric characteristics both of the connector itself and testing jigs. The latter's are to be removed to leave the connector's part only for the eye diagram prediction. This method can be verified further by SPICE simulation and measurement in this paper.

Information about the accurate soil moisture is crucial for agriculture. In the present work the Landsat-8, Sentinel-1 satellite data and Modified Water Cloud Model (MWCM) have been used to retrieve soil moisture from an agriculture area. The effect of crop canopy was incoporated in MWCM. The crop coverage was mapped from LANDSAT-8. Further, an account of the V1 and V2 vegetation and crop canopy’s primary and secondary descriptor were also estimated, respectively. Afterwards, a retrieval scheme of soil moisture was developed using dual polarizations (VH (Vertical characteristics signal send by radar/sensor, Horizontal characteristics signal received by radar/sensor) and VV (Vertical characteristics signal send by radar/sensor, Vertical characteristics signal received by radar/sensor)) available from the quad polarization of Sentinel-1 data. The model based soil moisture was compared with the observed soil moisture obtained from calibrated Time Domain Reflectometer (TDR). The model performance was evaluated with the help of statistical tests. The statistical tests result shows a good correlation between observed and estimated soil moisture (R2 = 0.86, 0.96, and 0.91, RMSE = 0.06, 0.03, and 0.02, RMSE% =2.0, 1.9, and 1.5) for different dates as: 17 January, 6 March and 15 April-2018, respectively. Therefore, this method has an operational potential for estimating soil moisture from area under crop.

Time-domain reflectometry (TDR) is a well-known measurement principle for evaluating frequency-dependent electric and dielectric properties of various materials and substances. Although TDR is a proven method, the high price for TDR measurement equipment and complex laboratory setups is often a limiting factor for cost-sensitive applications or large-scale field experiments, where a large number of TDR meters is required. This paper reports on the development of a new miniaturized low-cost TDR meter capable of sampling a repetitive rectangular waveform, which is used as an excitation signal. The developed sampling circuit is based on a digital delta modulator (DM) and allows for capturing the waveform of a repetitive measurement signal. A 1-MHz signal can be captured with a virtual sampling resolution of 1 ps within a measurement interval of 1 s. The generated pulses have a rise time of 2 ns and can be captured with an amplitude resolution of approximately 10 bit and an accuracy of approximately 8 bit. The developed digital DM architecture is implemented inside a small field programmable gate array and integrated into a miniaturized low-power TDR meter prototype for battery-powered outdoor applications. The captured measurement data are stored on integrated micro-SD card memory and can be read out either via a Universal Serial Bus, an RS-485 bus system, or a wireless interface. The TDR meter is controlled by an integrated microcontroller and a real-time clock and therefore can operate completely independent from any additional control setup. The TDR meter targets applications within the field of geoscience and agricultural monitoring, where large-scale measurement systems are required.

A simple optical reflectometry with a semiconductor optical amplifier ring structure is proposed for the first time to locate the accurate fiber fault position using the chaotic correlation detection method. The experimental results show that a much higher spatial resolution of about 50 μm and a measured stability of ±150 μm are achieved.

The increasing deployment of passive optical networks implies an equally increasing need for automatic monitoring systems. This article evaluates the feasibility of obtaining reliable information on fault position and loss by direct inspection of the optical time-domain reflectometry trace and via measurements of end-fiber reflectivity devices. Detailed calculations considering parameters often neglected, such as non-uniformity of splitters, fiber bending losses, as well as different Rayleigh backscattering factors and fiber attenuation coefficients, will be provided and experimentally verified. The limits and reliability of automated solutions for optical time-domain reflectometry passive optical network monitoring will be discussed.

A novel structure of ESD protection device based on the static induction thyristors (SITh) was in further investigation. Detailed analysis of the negative resistance characteristics of SITh was presented, especially its blocking and conducting states that satisfy the requirements in ESD events. The characteristics of SITh for ESD protection were obtained using the Time Domain Reflectometer (TDR) type of Transmission Line Pulse (TLP) testing system. The results illustrate that SITh for ESD protection has the following advantages: 1) It has a strong ESD stress handing capability (3.75 kV); 2) Its second breakdown current is large enough (2.5 A) to release great ESD current; 3) DC leakage current of SITh is very small (1 μA); 4) SITh can break through the limitations of transitional trigger voltages, whose trigger voltage is dynamically adjustable as well; 5) The ESD response time can be controlled through optimizing device structure of SITh.