Time Domain Reflectometry Research Articles

Unveiling the Sub-10 GHz Performance of SMA Connectors: A Comparative Analysis

This research review article provides a detailed examination of SMA (SubMiniature version A) connectors, which are integral components in high-frequency electronic systems. Through extensive S-parameter and time-domain reflectometry (TDR) measurements conducted on various SMA connector constructions, this study aims to evaluate the performance and impact of SMA connectors on signal integrity. Results reveal insights into the comparative performance of different SMA connector types mounted on PCB land pads, highlighting their strengths and limitations. Additionally, this paper explores the application of reference plane cut-outs for discontinuity impedance compensation, aiming to enhance the frequency response of SMA connectors. By linking measured performance parameters with relative market prices, this study offers valuable insights into the economic viability of different SMA connector types. The best and worst performing SMA connector measurements reveal an S11 < −10 dB bandwidth of more than 8 GHz and 1.5 GHz and a transition impedance of 46.5 Ω and 21 Ω, respectively. Overall, this research contributes to advancing the understanding and selection of SMA connectors for RF applications in telecommunications, aerospace, medical devices, and beyond.

Investigation and numerical simulation study on the vertical bearing mechanism of large-diameter overlength piles in water-enriched soft soil areas

Abstract With the development of urbanization, there is an increasing demand for higher land utilization rates, leading to the emergence of high-rise residential and commercial complexes. Additionally, in coastal areas, the presence of soft soil and low bearing capacity of the foundation necessitate higher foundation bearing capacity. Large-diameter, super-long piles have been widely employed in engineering projects to address these challenges effectively. This study analyzes their vertical bearing characteristics through field load tests and determines vertical load distribution and transfer mechanisms by using Brillouin Optical Time Domain Reflectometry. A numerical computation and analysis method based on PLAXIS 3D was established, examining the effects of parameters such as pile diameter, length, and soil modulus on the vertical bearing characteristics. Results indicate that large-diameter, super-long piles mainly bear loads through side friction, with the tip bearing less load. As load levels increase, axial force increases linearly above 40 m depth and becomes nonlinear below. Frictional resistance is significant below 40 m at 3,700 kN load. Parameter analysis shows that increasing pile length and diameter enhances bearing capacity, suggesting this method to improve pile foundation capacity in engineering.

Assessing Effect of Irrigation Frequency on Evaporation and Transpiration in Vineyards Using SIMDualKc Simulation Model with Measured Wet Fraction

Irrigation efficiency is important for the environment and the economy. SIMDualKc has been effectively used to calculate evaporation and transpiration separately in vineyards for different irrigation strategies, but not to analyze the impact of irrigation frequency. This study was conducted for the in-field adjustment of the soil wetted fraction (wf) with a time domain reflectometry (TDR) sensor as a function of different irrigation frequency treatments (T03, T07, and T15 with irrigation every 3, 7, and 15 days, respectively). Evaporation and transpiration values were estimated separately with the SIMDualKc model for different irrigation frequencies with the adjusted wf, comparing them with vineyard field measurements and analyzing the effect of different irrigation frequencies on vineyard yield. The wf in T15 was higher than that in T07, which in turn was higher than that in T03. SIMDualKc indicates the most unfavorable treatment to be the T07, with higher evaporation and lower transpiration than T15 and T03, while T15 had higher evaporation and lower transpiration than T03. Although stomatic conductance also indicates the most unfavorable case to be T07, no clear differences were found between T03 and T15. No statistically significant differences were obtained in yield. The results indicate that the differences observed between irrigation frequencies are not reflected in yield but do show up in water use efficiency.

Moisture patterns and fluxes in evolving tafoni developed in arkosic sandstone in temperate climate

AbstractCavernous weathering forms have long been studied and discussed as enigmas in geomorphology. Recently, their evolution has been shown to be controlled by moisture patterns, which are still poorly understood. For the first time, capillary water and vapor fluxes were characterized in detail at tafone in a temperate climate of central Europe using a wide range of methods adapted from soil hydrology. Time domain reflectometry showed that moisture flows from the rock interior to the evaporation front in the shallow subsurface of both — the backwalls and the outer surface. When overland flow occurs on the outer surfaces (after heavy rains), 10 mm/day can infiltrate and flow toward the backwalls. The main sources of water for tafone are the influx of water from the rock interior and the infiltration of overland flow after heavy rains, while condensation of air humidity is a minor source. Influx from the rock interior is coupled to the evaporation rate, which varies between 100 and 300 kg/m2/year in summer and less than 15 kg/m2/year in winter. More water evaporates from the backwall of the tafone than from the outer surface, and more salt is deposited in the backwalls, resulting in predominant salt weathering in the backwalls. The tafoni studied thus evolve, and the cavities deepen. Tafoni in arid and semi‐arid environments generally show a much higher contrast between evaporation rates from backwalls and outer surfaces than tafoni and honeycombs in temperate and coastal environments. Tafoni in temperate settings are therefore more susceptible to degradation when evaporation decreases or inflow to the tafone increases. This study also shows that microtensiometers can be used to determine moisture content with high spatial resolution, while time domain reflectometry allows accurate characterization of moisture patterns with depth.

An SNR Enhancement Method for Φ-OTDR Vibration Signals Based on the PCA-VSS-NLMS Algorithm.

To improve the signal-to-noise ratio (SNR) of vibration signals in a phase-sensitive optical time-domain reflectometer (Φ-OTDR) system, a principal component analysis variable step-size normalized least mean square (PCA-VSS-NLMS) denoising method was proposed in this study. First, the mathematical principle of the PCA-VSS-NLMS algorithm was constructed. This algorithm can adjust the input signal to achieve the best filter effect. Second, the effectiveness of the algorithm was verified via simulation, and the simulation results show that compared with the wavelet denoising (WD), Wiener filtering, variational mode decomposition (VMD), and variable step-size normalized least mean square (VSS-NLMS) algorithms, the PCA-VSS-NLMS algorithm can improve the SNR to 30.68 dB when the initial SNR is -1.23 dB. Finally, the PCA-VSS-NLMS algorithm was embedded into the built Φ-OTDR system, an 11.22 km fiber was measured, and PZT was added at 10.19-10.24 km to impose multiple sets of fixed-frequency disturbances. The experimental results show that the SNR of the vibration signal is 8.77 dB at 100 Hz and 0.07 s, and the SNR is improved to 26.17 dB after PCA-VSS-NLMS filtering; thus, the SNR is improved by 17.40 dB. This method can improve the SNR of the system's position information without the need to change the existing hardware conditions, and it provides a new scheme for the detection and recognition of long-distance vibration signals.

Mixed event separation and identification based on a convolutional neural network trained with the domain transfer method for a φ-OTDR sensing system

In phase-sensitive optical time domain reflectometer (φ-OTDR) based distributed acoustic sensing (DAS), correct identification of event types is challenging in complex environments where multiple events happen simultaneously. In this study, we have proposed a convolutional neural network (CNN) with a separation module and an identification module to simultaneously separate a mixed event into individual single-event components and identify each type of component contained in the mixed event. The domain transfer method is used in the training, fine-tuning, and testing of the proposed CNN, which saves 94% of the workload for massive DAS data collection and signal demodulation. A fine-tuning stage is added to minimize the impact of the dataset shift between the audio data and DAS data, hence enhancing the separation and identification performance. The model has good noise tolerance and achieves nearly 90% identification accuracy even at a relatively low signal-to-noise ratio (SNR). Compared with the conventional method using DAS data for training, domain transfer using a large amount of diverse audio data for training well generalizes the model to the target domain and hence provides more stable performance with only little degradation of identification accuracy.

Detecting Cracks in Intelligent Carbon-Based TRC Elements Through Wetting Events

Textile reinforced concrete (TRC) technology enables to construct sustainable and environmentally friendly thin-walled structural elements with self-sensory capabilities. The self-sensory concept is based on using high-strength and electrically conductive yarns that are simultaneously used as the main reinforcement system and as the sensory agent. By connecting the two ends of the yarns to either direct current (DC) or alternating current (AC) electrical circuits, it is possible to measure changes in the electrical readings and to further correlate them to the structural health. Studies in the literature validated the concept by using carbon yarns as hybrid monitoring agents. Most of them provided integrated assessments of global structural health but lacked the capability to pinpoint individual cracks. The current study offers a new identification procedure to locate cracks and to estimate their severity by combining two advanced monitoring procedures, that is by adopting the Time Domain Reflectometer (TDR) analysis; and by conceptually using the smart water leakage detection method. Both methods take advantage that a pair of carbon yarns can be positioned parallel to each other and connected to the DAQ system. In case of TDR method, one yarn functions as the signal transmitter and the other as insulation. In case of water leakage detection method, the electrical linkage between the two yarns changes the electrical characterization of the electrical circuit and enables the monitoring capabilities. The proposed study argues that a new identification procedure that benefits from each method can be developed and yields to smart identification procedure that has the capability to locate the crack and estimate its severity. The study will demonstrate the feasibility of the new procedure by experimental study. Results from this study will take a significant step toward developing reliable smart carbon-based TRC structures.

Shape Sensing of Resin Pipe with a Helical-winding Optical Fiber in Bending Test

In this study, we developed a shape-sensing technique for a pipe. An optical fiber was helically bonded on the outer surface of a resin pipe whose length, outer diameter and inner diameter are 3200 mm, 34 mm, and 26.6 mm, respectively. Firstly, four grooves were made on the surface along the pipe in a helical pattern with the same pitch of 360 mm. At the one pipe end, adjacent grooves were offset by 90 degrees and the offset was maintained along the pipe. The single-mode fiber was put into a groove and fixed by epoxy and then it was embedded into the adjacent groove. Consequently, the optical fiber was going back and forth twice along the pipe. At the pipe ends, there were stress-free fibers between the grooves. Shape sensing for the pipe is conducted as follows. 1. Strain distributions along the grooves are measured by a distributed fiber-optic strain sensing system. 2. The bending strain is extracted from the measured strain to calculate the curvature and bending angle. 3. The shape of the pipe is reconstructed based on the curvature and bending angle using the Frenet-Serret formulas. Three-point bending tests were conducted. In the tests, the pipe ends were clamped to be the fixed ends and a point load was applied to the pipe center. Strain distributions were measured by tunable wavelength coherent optical time domain reflectometry (TW-COTDR) or optical frequency domain reflectometry (OFDR). Then the pipe shape was reconstructed as described above. We compared the reconstructed shape with the deformation calculated by finite element analysis and the agreement was excellent. If we insert the developed pipe into a bedrock and reconstruct the pipe shape continuously, it is expected that we can detect cracks or damage in the bedrock. This approach is expected to make rock excavation constructions safer.

Robust instrumentation of composite pressure vessels manufactured via multi-filament winding for distributed fiber optic sensing

The development of hydrogen storage and transport technologies with safety, efficiency and economy is one of the main scientific and technological challenges to stablish the infrastructure for a hydrogen economy. The storage must not only be lightweight and compact but also safe, cost-effective, long-range and rapidly refuellable. Type IV composite pressure vessels have been recognized as a cost-efficient solution that can address these problems for on-board storage in the hydrogen-powered mobility and hydrogen transport in tube trailers. The demanding working environment presents a challenge to the failure analysis and predictive maintenance of composite pressure vessels; the knowledge of the precise condition of the pressure vessel is therefore mandatory to guarantee safety usage. The continuous strain monitoring of composite pressure vessels via distributed fiber optic sensors (DFOS) can enable the implementation of a structural health monitoring system. The robust instrumentation of composite pressure vessels with DFOS is here presented; the pressure vessel manufacture is based on the multi-filament winding. Small pressure vessel prototypes are designed and manufactured using carbon fibers as reinforcement; DFOS are integrated into the cylindrical section composite laminate during winding. A connector housing is placed on the dome section of the pressure vessel to protect sensor exit/entry points. The condition of the integrated DFOS is assessed throughout manufacture (winding and consolidation) via optical time domain reflectometry (OTDR). Afterwards, hydraulic burst tests are performed with step-wise pressure increments and the strain evolution and failure are monitored via distributed strain sensing. The integrated DFOS are capable of monitoring the strain evolution over the length of the vessel for the circumferential direction.

Effect of Biomass Water Dynamics in Cosmic-Ray Neutron Sensor Observations: A Long-Term Analysis of Maize-Soybean Rotation in Nebraska.

Precise soil water content (SWC) measurement is crucial for effective water resource management. This study utilizes the Cosmic-Ray Neutron Sensor (CRNS) for area-averaged SWC measurements, emphasizing the need to consider all hydrogen sources, including time-variable plant biomass and water content. Near Mead, Nebraska, three field sites (CSP1, CSP2, and CSP3) growing a maize-soybean rotation were monitored for 5 (CSP1 and CSP2) and 13 (CSP3) years. Data collection included destructive biomass water equivalent (BWE) biweekly sampling, epithermal neutron counts, atmospheric meteorological variables, and point-scale SWC from a sparse time domain reflectometry (TDR) network (four locations and five depths). In 2023, dense gravimetric SWC surveys were collected eight (CSP1 and CSP2) and nine (CSP3) times over the growing season (April to October). The N0 parameter exhibited a linear relationship with BWE, suggesting that a straightforward vegetation correction factor may be suitable (fb). Results from the 2023 gravimetric surveys and long-term TDR data indicated a neutron count rate reduction of about 1% for every 1 kg m-2 (or mm of water) increase in BWE. This reduction factor aligns with existing shorter-term row crop studies but nearly doubles the value previously reported for forests. This long-term study contributes insights into the vegetation correction factor for CRNS, helping resolve a long-standing issue within the CRNS community.

Time domain reflectometry coil probes for measuring thin surface layer soil moisture: Field tests over 21 years (2002–2022) under highly variable climate conditions in Mongolia

A coil probe (CP) for time-domain reflectometry (TDR) with a sensor length of 40 mm (CP40) was developed for long-term field soil moisture measurements in a thin surface soil layer (0–3 cm depth). In laboratory, soil moisture measurements of CP40 were nearly identical to those of a traditional two-rod type TDR (2RTDR) probe (rod length: 15 cm, diameter: 0.3 cm, spacing: 3 cm). The CP40 measurement accuracy was between 0.01 m3/m3 and 0.03 m3/m3. For long-term field soil moisture measurements, five CP40 units were installed in the highly wetted soil at the Sanzai site (SS), which is in the permafrost area of the Taiga, and dry soil at the Mandalgobi site (MGS) in the semi-arid area of Mongolia. Four units accurately measured soil moisture at both sites over six years (2002–2007and 2008–2009). Three units succeeded in conducting precisely continuous soil moisture measurements between 2008 and 2022 at the MGS. Two units successfully measured soil moisture over 21 years at both the sites. The representativeness of the CP40 soil moisture measurements in highly wetted soils was low because of heavy rainfall and soil heterogeneity. The accuracy of CP40 soil moisture measurements in highly wetted soils was slightly lower than that of the traditional 2RTDR probe. However, the accuracy of the CP40 soil-moisture measurements in the dry soil was comparable to that of the traditional 2RTDR probe. CP40 units are durable and their field soil moisture measurements demonstrate stable and precise performance (bias, RMSE), even under severe environmental conditions.

Evaluation of electrical resistivity of cement-based materials using time domain reflectometry

Time domain reflectometry (TDR) is a widely used electromagnetic wave–based technique for evaluating the volumetric water content of soils, although its use for moisture measurement in cement-based materials is limited. This paper presents a comprehensive analysis of the electrical properties of cement pastes and cement paste–slime mixtures using TDR. Both TDR and electrical resistivity probes are used to estimate the electrical resistivities of various cement-based materials over their curing period. The study reveals that these properties are significantly influenced by curing time, water–cement ratio, and water–solid ratio. The experimental results demonstrate a consistent increase in electrical resistivity with curing time, underscoring the significant role of hydration-induced water evaporation and microstructural changes. Furthermore, the interpretation of characteristic voltages on the TDR waveform significantly influences resistivity estimates. Thus, this study highlights the potential of TDR in accurately evaluating the electrical resistivity of cement-based materials.

Mapping agricultural soil water content using multi-feature ensemble learning of GPR data

Soil water content (SWC) is significant for understanding and evaluating the conditions of soils and plants. Since traditional methods such as time domain reflectometry (TDR) and neutron probes have significant drawbacks such as limitations in spatial resolution, detection depth, efficiency, and non-destruction, ground penetrating radar (GPR) has become a potential method in SWC estimation. Many features extracted from GPR data in the time and frequency domain have been proven to be sensitive to the SWC and can further achieve the estimation of it. However, the methods based on these features are easy to be interfered with by noise and the heterogeneity in soils. This article aims to solve this problem by including more features and integrating these features for a joint estimation. Firstly, we study the relationships between SWC and seven features extracted from GPR data. Consequently, we propose to include new features, i.e. the loss tangent feature and the time-frequency features, in the SWC inversion. Secondly, we achieve the multi-feature ensemble learning based on the Adaboost R. method, which largely enhances the accuracy of SWC inversions compared to the single-feature estimations. During the numerical test, we establish the stochastic medium to model the heterogeneity in the real soil. The test verifies the effectiveness and the robustness of the proposed method. Finally, a field experiment is performed on the transition zone of no-tillage and deep-ploughing croplands. A 2-D SWC map is obtained which distinctly presents the SWC difference between the two regions. Our study provides a new approach to improve the accuracy of SWC estimation using GPR.

Curing process monitoring of cementitious grout using time domain reflectometry (TDR) system

Curing process monitoring of the cementitious grout is necessary for its successful use and to ensure the serviceability of the constructed, repaired, and stabilized infrastructures using that material. In this study, time domain reflectometry (TDR) system is applied to monitor the curing process of the cementitious grout based on the changes in relative permittivity (εr). To utilize the TDR system to electrically conductive cementitious grout, a TDR probe with coated core electrode (coated probe) is manufactured, and a calibration is performed to evaluate the formal εr by using the coated probe. The coated probes are installed in the middle and at the bottom of the cementitious grouts with a length of 950 mm, and the εr have been evaluated with curing time using both middle probe (εr(middle)) and bottom probe (εr(bottom)). In addition, compressive strength tests are performed on separately prepared specimens for comparative analyses. Experimental results show that the εr(middle) and εr(bottom) decrease with curing time and converge from the fully cured time, and the curing process of cementitious grout monitored by the TDR system is consistent with the compressive strength developments of the specimens tested with curing time. Therefore, the TDR system with a coated probe may effectively be used for monitoring the curing process of the cementitious grouts based on the changes in electromagnetic property.

Enhanced perturbation measurement range chirped pulse ϕ-OTDR for distributed static measurements using feedback frequency-shift compensation technology

Chirped-pulse phase-sensitive optical time-domain reflectometry (CP-ϕOTDR) is a newly developed distributed optical fiber sensing (DOFS) technology that can measure physical quantities across the length of optical fiber. The measurement of perturbations as strain or temperature changes is performed by comparing the time domain trace of Rayleigh backscattered (RBS) light with a reference trace. However, large strain or temperature fluctuations or laser frequency noises necessitate frequent updates of the reference, and short-term change measurements must be integrated to obtain absolute strain or temperature, which introduces a 1/f noise component due to the combination of noise with each cumulative change. In this study, we propose a novel CP-ϕOTDR system based on frequency-shift compensation (FSC) technology. This system utilizes real-time feedback control of the central frequency of the incident laser to compensate for time domain trace distortion caused by large perturbations. It overcomes the limitations associated with the total chirp bandwidth and eliminates the 1/f noise component by obviating the need for frequent updates of the reference trace. The measuring range for perturbations is only limited to the wavelength range supported by the integrated optical devices, typically on the order of nanometers, corresponding to at least tens of Kelvin in temperature fluctuations or hundreds of micro-strains. To validate the effectiveness, we conducted a temperature measurement experiment involving a 1 K variation, which is about 90 times the maximum measurable perturbation that the original CP-ϕOTDR system can demodulate with the reference unchanged. The results demonstrate that the FSC method significantly expands the perturbation measurement range of the CP-ϕOTDR system.

Characterization of cement–slime mixture using time domain reflectometry

This study explores the electromagnetic characteristics of five cement–slime mixtures using two types of time domain reflectometry sensors. For 28 days of curing, compressive strength tests are conducted and electromagnetic signals are measured. The electromagnetic wave velocity and corresponding apparent permittivity are calculated, and the relationships between these properties and the compressive strengths of the mixtures are established. Results show that in the initial curing period, capturing the apparent permittivity using a conventional probe proves difficult due to the high electrical conductivity of the mixtures. In contrast, an insulated electrical wire can detect reflected signals across all slime ratios, but it exhibits less sensitivity to changes in the electromagnetic signal. The apparent permittivity decreases exponentially over the curing time, influenced by the hydration process. Strong correlations are found between the apparent permittivities derived from both sensors and between decreasing apparent permittivity and increasing compressive strength.

Influence of Pump Light on LP01 and LP11 Modes in Few-Mode Fiber Brillouin Optical Time Domain Reflectometry

The quality of pump pulse in few-mode-fiber Brillouin optical time domain reflectometry (FMF-BOTDR) is vital for the spontaneous Brillouin scattering of modes LP01 and LP11 because it is the comprehensive effect of the main laser linewidth and pulse width, which is firstly discussed as we know. Numerical and experimental analysis are made for the amplitude and linewidth distribution, corresponding to the signal–noise ratio (SNR) and frequency resolution in BOTDR, respectively. Simulation shows the linewidths and peak values of Brillouin scattering have the same tendency for the LP01 mode and LP11 mode when the laser linewidth is less than 1 MHz but decreases slowly until they are the same when the laser linewidth is wider than 1 MHz. With the pulse width widening, the Brillouin linewidths for LP01 and LP11 modes both decrease sharply, almost to the natural linewidth of fiber 41 MHz and 35 MHz. Experimental results show that the amplitude distribution for the LP01 mode is always larger than for the LP11 mode if the main laser has the same linewidth and the frequency fluctuation is at least 2 MHz with the fiber laser and LP11 mode. The above results could provide improved sensing resolution for FMF-BOTDR sensing system.

Distributed Optical Fiber-Based Radiation Detection Using an Ultra-Low-Loss Optical Fiber

The combination of an ultra-low-loss optical fiber sensitive to ionizing radiation and an optical time domain reflectometer (OTDR) is investigated to explore the feasibility of a single-ended distributed radiation detector. The peculiarity of the tested fiber resides in its regenerative high radiation-induced attenuation (RIA) response in the infrared spectrum (1310 nm), which returns to a low value once the irradiation has ended, combined to its sensitivity, highly increasing with the dose rate. In this work, only some sections of the fiber line were irradiated with 100 kV X-rays at room temperature, to prove the spatially resolved radiation detection capabilities of the system. The transient RIA response of the fiber was characterized at different pre-irradiation doses. A pre-irradiation treatment was shown to stabilize the optical fiber response, improving its RIA vs. dose rate linearity and repeatability. This improved response, in terms of radiation quantification, comes at the cost of a lower detection threshold. This work lays the bases for a distributed radiation detector, with some capabilities in dose rate evaluation.

Using 5TE Sensors for Monitoring Moisture Conditions in Green Parks.

The ground surface and subsurface of green parks in arid and desert areas may be subjected to desiccation as a result of weather and hot temperatures. It is not wise to wait until plants are turning pale and yellow before watering is resumed. Given the scarcity of water in typical desert zones, we recommend full control of irrigation water. This study presents a method of recycling irrigation water using 5TE sensors, employing time-domain reflectometry (TDR) technology. A trial test section was constructed along the coast of the eastern province of Saudi Arabia. Water recycling involves using clay-sand liners placed below the top agricultural soils to intercept excess water and direct it towards a collection tank, and then it is pumped out to a major water supply tank. The main properties of soils and clay-sand liners normally taken into account include moisture content, density, and hydraulic conductivity. An assessment of geotechnical properties of clay-sand mixtures containing 20% clay content was conducted. The profiles of moisture and temperature changes were monitored using 5TE sensors and data loggers. The 5TE sensors provided continuous measurements at varying temperatures and watering cycles. Twenty-nine watering cycles were conducted over a six-month period. An additional section was considered with a liner consisting of the same clay but enhanced with bentonite as one-third of the clay content. The volumetric water content was found to vary from 0.150 to 0.565 following changing weather and direct watering cycles. The results indicated that the use of a TDR instrumentation is a cost-effective and time-saving technique to construct a system for saving irrigation water.

Modeling and simulation of [formula omitted]-OTDR system suitable for underwater intrusion detection and classification

Security of certain locations is of utmost importance. The contemporary works cater to locate the perturbations for the land based installations using the fiber optic based sensors. Intrusion detection for underwater environment is quite critical because of the high false alarm rates. Phase-optical time domain reflectometer (Φ-OTDR) has recently become prominent as it supports distributed acoustic sensing (DAS) utilizing optical fiber as a sensor. The benefit of developing a numerical model of the actual sensing system is that it mimics the strain developed in the fiber due to external acoustic perturbation which in turn changes the characteristics of the Rayleigh backscattered wave. Hence, we propose a numerical model based on the coherent Φ-OTDR set-up for undersea perturbation detection and classification. An intruder model is developed that determines the received pressure level at the fiber (sea depth) by considering the total transmission loss due to the simultaneous ships sailing at a pre-established distance from one another. The efficacy of the numerical model of the Φ-OTDR system is determined by firstly matching it’s outcomes with the experimental results for multiple sinusoidal disturbances acting at different locations on the fiber. Further, the numerical model is used to detect different ship sounds in underwater environment using feature extraction and frequency–time–energy relation. In addition, a complete pipeline to classify type of intruders is stated in detail.