Fiber-Optic Telecommunication Network Wells Monitoring by Phase-Sensitive Optical Time-Domain Reflectometer with Disturbance Recognition.

The paper presents the application of a phase-sensitive optical time-domain reflectometer (phi-OTDR) in the field of urban infrastructure monitoring. In particular, the branched structure of the urban network of telecommunication wells. The encountered tasks and difficulties are described. The possibilities of usage are substantiated, and the numerical values of the event quality classification algorithms applied to experimental data are calculated using machine learning methods. Among the considered methods, the best results were shown by convolutional neural networks, with a probability of correct classification as high as 98.55%.

Non-Invasive Acoustic Monitoring of Gas Turbine Units by Fiber Optic Sensors.

In this article, we study the possibility of gas turbine unit (GTU) monitoring using interferometric fiber optic sensors. We used the Mach-Zehnder interferometer (MZI) scheme, which can be easily implemented and simply installed on the turbine, and also allows us to solve the problem of phase unwrapping conveniently. In this research, the following main steps were carried out: an experimental scheme based on the MZI was assembled, and its sensitive arm was fixed on the GTU under study; data on various operation modes of the GTU was collected; the data were subjected to frequency FFT analysis, based on which the main rotational speeds of the turbine were identified. With FFT analysis, we also demonstrated multiples harmonics, which appear in the case of GTU after operating time, caused by the number of blades. The possibility of GTU monitoring and analysis using a non-invasive compact fiber-optic sensor is demonstrated: spectral analysis is used to detect the rotor speed, as well as the presence or absence of high-order multiple frequencies indicating blade and bearing defects, which are determined by the number of GTU's blades and rolling bearing used as turbines rotor supports.

Distributed Acoustic Sensor Using a Double Sagnac Interferometer Based on Wavelength Division Multiplexing.

We demonstrated a fiber optic distributed acoustic sensor based on a double Sagnac interferometer, using two wavelengths separated by CWDM modules. A mathematical model of signal formation principle, based on a shift in two signals analysis, was described and substantiated mathematically. The dependence of the sensor sensitivity on a disturbance coordinate and frequency was found and simulated, and helped determine a low sensitivity zone length and provided sensor scheme optimization. A data processing algorithm without filtering, appropriate even in case of a high system noise level, was described. An experimental study of the distributed fiber optic sensor based on a Sagnac interferometer with two wavelengths divided countering loops was carried out. An accuracy of 24 m was achieved for 25.4 km SMF sensing fiber without phase unwrapping.

Scientific Applications of Distributed Acoustic Sensing: State-of-the-Art Review and Perspective.

This work presents a detailed review of the development of distributed acoustic sensors (DAS) and their newest scientific applications. It covers most areas of human activities, such as the engineering, material, and humanitarian sciences, geophysics, culture, biology, and applied mechanics. It also provides the theoretical basis for most well-known DAS techniques and unveils the features that characterize each particular group of applications. After providing a summary of research achievements, the paper develops an initial perspective of the future work and determines the most promising DAS technologies that should be improved.

Study of Intra-Chamber Processes in Solid Rocket Motors by Fiber Optic Sensors.

In this study, an experimental study of the burning rate of solid fuel in a model solid propellant rocket motor (SRM) E-5-0 was conducted using a non-invasive control method with fiber-optic sensors (FOSs). Three sensors based on the Mach-Zehnder interferometer (MZI), fixed on the SRM E-5-0, recorded the vibration signal during the entire cycle of solid fuel burning. The results showed that, when using MZI sensors, the non-invasive control of solid fuel burnout is made possible both by recording the time of arrival of the combustion front to the sensor and by analyzing the peaks on the spectrogram of the recorded FOS signal. The main mode of acoustic vibrations of the chamber of the model SRM is longitudinal, and it changes with time, depending on the chamber length. Longitudinal modes of the combustion chamber were detected by MZI only after the combustion front passed its fixing point, and the microphone was unable to register them at all. The results showed that the combustion rate was practically constant after the first second, which was confirmed by the graph of the pressure versus time at the nozzle exit.

Sensitivity Improvement of Phi-OTDR by Fiber Cable Coils.

We present a theoretical and experimental study in which we increased the sensitivity of a phase-sensitive optical time-domain reflectometer (phi-OTDR). This was achieved by constructing coils in the sensor cable, which increased the total amplitude of the impact on the fiber. We demonstrate this theoretically using the example of a phase-sensitive reflectometer model and practically in testing grounds with a buried nearby conventional sensor and a sensor with coils. The sensitivity increased 2.2 times. We detected 95% of events when using coils, versus 20% when using a straight cable. The suggested method does not require any modifications to the device.

Serological Evidence of Hepatitis E Virus Circulation Among Reindeer and Reindeer Herders.

Various deer species are infected with hepatitis E virus (HEV) and may be a source of zoonotic infection for humans. So far, HEV has not been isolated from reindeer and the role of this domesticated deer species in HEV transmission is unknown. We tested serum samples from 191 reindeer (Rangifer tarandus) and 86 adult reindeer herders from the circumpolar regions of Yakutia (Russian Federation) for anti-HEV and HEV RNA. Anti-HEV IgG prevalence was 12.0% (95% confidence interval [95% CI]: 8.1-17.5) in reindeer and 4.7% (95% CI: 1.5-11.7) in reindeer herders. The latter was similar to the positivity rate observed in adult residents of the city of Yakutsk, the capital of Yakutia, who do not have routine contact with reindeer (3.7% [19/519, 95% CI: 2.3-5.7]). No samples positive for HEV RNA were identified. The study provides evidence of HEV circulation in reindeer. Nevertheless, the low seroprevalence in reindeer herders indicate a low risk of zoonotic HEV infection.

The Sensitivity Improvement Characterization of Distributed Strain Sensors Due to Weak Fiber Bragg Gratings.

Weak fiber Bragg gratings (WFBGs) in a phase-sensitive optical time-domain reflectometer (phi-OTDR) sensor offer opportunities to significantly improve the signal-to-noise ratio (SNR) and sensitivity of the device. Here, we demonstrate the process of the signal and noise components' formation in the device reflectograms for a Rayleigh scattering phi-OTDR and a WFBG-based OTDR. We theoretically calculated the increase in SNR when using the same optical and electrical components under the same external impacts for both setups. The obtained values are confirmed on experimental installations, demonstrating an improvement in the SNR by about 19 dB at frequencies of 20, 100, and 400 Hz. In this way, the minimum recorded impact (at the threshold SNR = 10) can be reduced from 100 nm per 20 m of fiber to less than 5 nm per 20 m of fiber sensor.

Symposium report: emerging threats for human health - impact of socioeconomic and climate change on zooanthroponosis in the Republic of Sakha (Yakutia), Russia.

Population growth, socio-cultural and economic changes as well as technological progress have an immediate impact on the environment and human health in particular. Our steadily rising needs of resources increase the pressure on the environment and narrow down untainted habitats for plants and wild animals. Balance and resilience of ecosystems are further threatened by climate change, as temperature and seasonal shifts increase the pressure for all species to find successful survival strategies. Arctic and subarctic regions are especially vulnerable to climate change, as thawing of permafrost significantly transforms soil structures, vegetation and habitats. With rising temperature, the risk of zoonotic diseases in the Republic of Sakha (Yakutia) has also increased. As vegetation periods prolong and habitats broaden, zoonotic pathogens and their vectors find more favourable living conditions. Moreover, permafrost degradation may expose historic burial grounds and allow for reviving the vectors of deadly infections from the past. To assess the current state of knowledge and emerging risks in the light of the "One Health" concept, a German-Russian Symposium took place on 13 August 2018 in Yakutsk, Russian Federation. This symposium report presents the main findings generated from presentations and discussions.