Limits of performance of chirped- pulse phase-sensitive OTDR

Distributed acoustic sensing is an emerging field of research which aims to develop methods capable of using a single optical fiber as a long, dense, and high-sensitivity sensor array. Currently, the most promising implementations measure the interference of Rayleigh backscattered light, obtained by probing the fiber with light from a source of high coherence. These methods are known as Phase-sensitive Optical Time-Domain Reflectometers (φOTDR), and are currently undergoing a period of active research and development, both academically and industrially. One of its variants, known as the Chirped-Pulse φOTDR (CP-φOTDR), was developed in 2016. This technique has proven to be remarkably sensitive to strain and temperature, with an attractively simple implementation. In this thesis, we delve into the intricacies of this technique, probing its fundamental limits and addressing current limitations. We discuss the implications of estimation on the performance statistics, the impact of different noise sources and the origin of cross-talk between independent measured positions. In doing so, we also propose methods to reach the current fundamental limitations, and overcome the upper bound of measurable perturbations. We then demonstrate new potential applications of the technique: in seismology, by exploiting the high spatial density of measurements for array signal processing; in the fast characterization of linear birefringence in standard single-mode fibers; and on the measurement of sound pressure waves, by using a special flat cable structure to embed the fiber under test. Finally, we summarize and comment on the aforementioned achievements, proposing some open lines of research that may originate from these results.Distributed acoustic sensing is an emerging field of research which aims to develop methods capable of using a single optical fiber as a long, dense, and highsensitivity sensor array. Currently, the most promising implementations measure the interference of Rayleigh backscattered light, obtained by probing the fiber with light from a source of high coherence. These methods are known as Phase-sensitive Optical Time-Domain Reflectometers (φOTDR), and are currently undergoing a period of active research and development, both academically and industrially. One of its variants, known as the Chirped- Pulse φOTDR (CP-φOTDR), was developed in 2016. This technique has proven to be remarkably sensitive to strain and temperature, with an attractively simple implementation. In this thesis, we delve into the intricacies of this technique, probing its fundamental limits and addressing current limitations. We discuss the implications of estimation on the performance statistics, the impact of different noise sources and the origin of cross-talk between independent measured positions. In doing so, we also propose methods to reach the current fundamental limitations, and overcome the upper bound of measurable perturbations. We then demonstrate new potential applications of the technique: in seismology, by exploiting the high spatial density of measurements for array signal processing; in the fast characterization of linear birefringence in standard single-mode fibers; and on the measurement of sound pressure waves, by using a special flat cable structure to embed the fiber under test. Finally, we summarize and comment on the aforementioned achievements, proposing some open lines of research that may originate from these results

Steady-Sensitivity Distributed Acoustic Sensors

Distributed acoustic sensors (DAS) based on phase-sensitive optical time-domain reflectometry (phiOTDR) have demonstrated interesting performance for many applications ranging from seismology to pipeline protection. However, the sensitivity of traditional DAS relying on coherent detection is strongly dependent on the system noise and trace fading points, offering poor reliability of the results in the spatial dimension. In this manuscript, we evaluate the statistical performance of a recently proposed DAS technique, namely, chirped-pulse phiOTDR, in terms of sensitivity and signal-to-noise ratio (SNR). Our results show behavioral trends that significantly differ from those of traditional DAS. In particular, the acoustic SNR distribution in chirped-pulse DAS is notably narrower than that in the traditional case, allowing to ensure a large system dynamic range across all the points of the optical trace. Hence, chirped-pulse phiOTDR offers localized perturbation detection with very high reliability, almost independent of trace fading points, along the complete reachable range of the sensor.European CommissionMinisterio de Economía y CompetitividadComunidad de Madri

Monitoring of remote seismic events in metropolitan area fibers using distributed acoustic sensing (DAS) and spatio-temporal signal processing

Este documento se considera que es una ponencia de congresos en lugar de un capítulo de libro.Optical Fiber Communication Conference (OFC) 2019, San Diego, California, USA, 3-7 March 2019Remote seismic activity is monitored with DAS using a pre-existent fiber installation in an urban area. Background noise, which greatly exceeds the amplitude of the monitored seismic signals, is eliminated via 2D (spatio-temporal) signal processing

Extending the Measurement of True Dynamic Strain via Chirped-Pulse Phase-Sensitive Optical Time Domain Reflectometry to 100's of Microstrains

26ª edición del congreso internacional Optical Fiber Sensors (OFS26), 24/09/2018-28/09/2018, Lausanne, Suiza.It is experimentally demonstrated that a chirped pulse phase-sensitive OTDR can measure large and fast dynamic strains (~100’s of µε, ~100’s of Hz) with SNR of ≥ 24dB. Signal smoothing and impact of error accumulation are also discussed.European Commissio

Distributed detection of hydrogen and deuterium diffusion into a single-mode optical fiber with chirped-pulse phase-sensitive optical time-domain reflectometry

For some infrastructures like oil and gas extraction boreholes or radioactive waste repositories, where distributed optical fiber sensors are employed to grant the safety of the facilities, the presence of gas species such as hydrogen or deuterium is one more relevant parameter to monitor. The possibility of employing the same kind of sensors for this purpose is of special interest, reducing the cost by employing a single interrogator, able to measure more than one parameter by simply employing an adequate sensing fiber. To meet this goal, we present here a sensor based on Chirped Pulse Phase sensitive Optical Time Domain Reflectometry, which is able to detect these species while they diffuse into the silica fiber core. Its ability to measure the induced change of its refractive index with a sensitivity around 10 8 has allowed determining hydrogen concentration in the silica core with precision in the order of 10 3 mol/m3 and spatial resolution ~6 m, while also providing an indirect measurement of the solubility of deuterium in a standard telecom-grade optical fiber.Commission of the European Communities JointMinisterio de Economía y CompetitividadMinisterio de Ciencia, Innovación y UniversidadesComunidad de Madri

Analysis of disturbance-induced "virtual" perturbations in chirped pulse φ-OTDR

When a disturbance acts on a fiber it induces a change in the local refractive index that influences the fiber backscattering trace. If a chirped pulse φ-OTDR setup is used to interrogate the fiber, this refractive index change appears as a local shift of the received trace, linear to the acting perturbation. However, the refractive index change influences the round trip time of all the backscattering components generated by further fiber sections as well. Due to the high sensitivity of chirped pulse φ-OTDR, the change in the round trip time of the backscattering components, which is usually negligible, may appear as a virtual perturbation in certain conditions. In this letter we derive a mathematical model for the virtual perturbation induced by a disturbance acting on the fiber, when the measurement is performed by a chirped pulse φ-OTDR. We experimentally validate the model by inducing a temperatura change on a known span of fiber while monitoring its effects in a further fiber section kept at rest. The experimental results are then analyzed and compared with the theoretical ones.European CommissionMinisterio de Economía y CompetitividadMinisterio de Ciencia, Innovación y UniversidadesComunidad de Madri

Photonic Seismology

International Photonics and OptoElectronics Meetings 2019, OFDA, 11/11/2019-14/11/2019, Wuhan, ChinaOne of the greatest outstanding challenges in seismology is the sparsity of instrumentation across the Earth, particularly in the oceans. In this work we show that optical fiberbased distributed acoustic sensors (DAS) can represent a low-cost solution (basically inexistent so far) for monitoring seismicity in remote areas of the ocean. This solution can retrofit existing telecommunication optical fiber cables lying in the ocean and transform them (with no basic change in the cable itself) into powerful seismic sensing arrays. With a single optoelectronic unit in the end of the cable (onshore), a full span of 50-100 km can be monitored, with thousands of measuring points interrogated.Commission of the European Communities JointMinisterio de Economía y CompetitividadMinisterio de Ciencia, Innovación y UniversidadesComunidad de Madri

Monitorización de actividad sísmica usando sensores distribuidos en fibra basados en φOTDR y pulsos con chirp

XI Reunión Española de Optoelectrónica (OPTOEL 2019), 03/07/2019-05/07/2019, Zaragoza, España.Actualmente, los sistemas de comunicaciones ópticas de larga distancia se basan en una extensa red de fibra óptica que se encuentra instalada alrededor del globo. En este trabajo, presentamos cómo esta red de fibra puede ser empleada para un uso alternativo: el análisis de movimientos sísmicos del planeta. Para ello, se ha utilizado la fibra como elemento sensor en un sistema de sensado distribuido basado en OTDR sensible a fase (φOTDR) usando pulsos con chirp con el que se ha detectado un terremoto de grado 8,2 ocurrido el pasado agosto en las Islas Fiji. Este terremoto se ha detectado en dos localizaciones diferentes, un entorno metropolitano en la ciudad de Pasadena (California, EEUU) y un entorno submarino en la costa de Bélgica. Usando técnicas de procesado lineales se ha podido ex-traer información del terremoto del ruido ambiente. Los resultados aquí mostrados muestran el gran potencial de la red de fibra ya instalada para su uso como sismógrafo distribuido.Ministerio de Economía y CompetitividadComunidad de MadridEuropean Commissio

PATHOLOGIES CAUSED BY INFILTRATION IN A LONG-STAY INSTITUTION FOR THE ELDERLY: A CASE STUDY

This paper is part of an extension project aimed at renovating the Carlos Romeiro Asylum, located in Conselheiro Lafaiete, Minas Gerais, starting from an initial conception about the current state of the building. For this, it was developed a literature review on the main cause of pathologies that affect the building, infiltration and humidity damage, and others. A case study will be presented, showing the main physical deficiencies of this resting house, to propose interventions based on Material Science and Civil Engineering. Because it is a place where the construction work must be done concomitantly with the circulation of people, this project needs to be divided into stages. It is important to point out that this work may involve both recovery materials and methods, which aim to reestablish the original conditions of the damaged structures, and reinforcement, which aim to adjust the resistant capacity of the structures according to their use. The development and application of this project will bring improvements to the elderly population of the asylum, enabling better health and mobility conditions inside the space where more than sixty old people live.Este trabajo forma parte de un proyecto de ampliación que pretende reformar el Asilo Carlos Romeiro, una Institución de Larga Estancia para Ancianos situada en Conselheiro Lafaiete, Minas Gerais, a partir de una concepción inicial sobre el estado actual del edificio. Para ello, se elaboró una revisión bibliográfica sobre la principal causa de patologías que afectan al edificio, las infiltraciones y los daños por humedad, entre otros. Se presentará un estudio de caso, mostrando las principales deficiencias físicas de esta residencia de ancianos, para proponer intervenciones basadas en la Ciencia de los Materiales y la Ingeniería Civil. Al tratarse de un lugar donde las obras deben realizarse de forma concomitante con la circulación de personas, este proyecto debe dividirse en etapas. Es importante señalar que este trabajo puede implicar materiales y métodos de recuperación, que tienen como objetivo restaurar las condiciones originales de las estructuras dañadas, y de refuerzo, que tienen como objetivo ajustar la capacidad resistente de las estructuras de acuerdo con su uso. El desarrollo y aplicación de este proyecto aportará mejoras a la población anciana del asilo, permitiendo mejorar las condiciones de salud y movilidad dentro del espacio donde viven más de sesenta ancianos. Traducción realizada con la versión gratuita del traductor www.DeepL.com/TranslatorEste trabalho faz parte de um projeto de extensão que visa a reforma do Asilo Carlos Romeiro, Instituição de Longa Permanência de Idosos localizada em Conselheiro Lafaiete, Minas Gerais, a partir de uma concepção inicial sobre o estado atual do edifício. Para isso, foi desenvolvida uma revisão biblio literatura sobre a principal causa de patologias que afetam o edifício, infiltração e danos à umidade, entre outras. Será apresentado um estudo de caso, mostrando as principais deficiências físicas desta casa de repouso, para propor intervenções baseadas em Ciência material e Engenharia Civil. Por ser um local onde as obras devem ser feitas concomitantemente com a circulação de pessoas, esse projeto precisa ser dividido em etapas. É importante ressaltar que este trabalho pode envolver materiais de recuperação e métodos, que visam restabelecer as condições originais das estruturas danificadas, e reforço, que visam ajustar a capacidade resistente das estruturas de acordo com seu uso. O desenvolvimento e a aplicação deste projeto trarão melhorias para a população idosa do asilo, possibilitando melhores condições de saúde e mobilidade dentro do espaço onde vivem mais de sessenta idosos

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio