Sistema Distribuído de Detecção Acústica de Fibra Óptica DAS-INNO

Definition of Distributed Fiber Optic Acoustic Sensing

Distributed Acoustic Sensing System (O) is a fiber optic optoelectronic device that measures acoustic interactions along the length of the fiber optic sensing cable.

The unique feature of a distributed acoustic sensing system is that it provides a continuous (ou distribuído) distribuição de temperatura ao longo do comprimento do cabo sensor, rather than at discrete sensing points.

Distributed acoustic sensing technology

Geralmente, DAS technology uses standard telecommunications fiber optic cables, and specialized fiber optic cables are only required at high temperatures (greater than 100 °C). Sensing fibers are usually based on single-mode fibers, although some specialized applications use multi-mode sensing fibers.

O alcance de um sistema DAS é geralmente de até 50 km por fibra sensora, e cada unidade de inquérito geralmente tem 1 ou 2 canais que podem ser operados simultaneamente. Por exemplo, DAS pode medir até 100 km, e unidades de 2 canais podem medir 50 km em qualquer direção.

princípio de medição

A unidade de interrogação do sensor acústico distribuído transmite pulsos de laser para a fibra óptica. Quando este tipo de pulso de luz se propaga ao longo da fibra, a interação dentro da fibra causa reflexão da luz chamada retroespalhamento, que é determinado por pequena deformação (ou vibração) eventos dentro da fibra, que são causados pela energia sonora local. Esta luz retroespalhada se propaga para cima ao longo da fibra óptica até a unidade de interrogatório, onde é amostrado na frequência Rayleigh. O tempo necessário para os pulsos de laser permite o mapeamento preciso dos eventos de retroespalhamento para a distância da fibra – this is known as an optical time-domain reflectometer.

Most distributed acoustic sensing systems on the market today are based on a principle called Coherent Optical Time Domain Reflectometer (COTDR).

Spatial resolution and spatial sampling period

The spatial resolution is mainly determined by the duration of the emitted pulse, and a resolution of 10m given by a 100ns pulse is a typical value. The amount of reflected light is proportional to the pulse length, so there is a trade-off between spatial resolution and maximum range. In order to improve the maximum range, it is hoped to use longer pulse lengths to increase the level of reflected light, but this leads to greater spatial resolution. Tipicamente, the spatial resolution of most systems is 5-10 metros.

Comparison between DAS and other fiber optic distributed sensing systems

There are many other fibra óptica distribuída sensing technologies that rely on different scattering mechanisms and can be used to measure other parameters.

Brillouin based systems are commonly used to measure distributed strain and temperature.
Brillouin scattering is much weaker than Rayleigh scattering, so reflections from multiple pulses must be added together to enable measurement. Portanto, the maximum frequency for measuring changes using Brillouin scattering is usually several tens of Hz, while Rayleigh based COTDR DAS systems have kHz sensitivity.

Raman based systems are commonly used for temperature measurement, while DTS systems are typically based on Raman technology. The intensity of Raman scattering is even lower than that of Brillouin scattering, so it usually takes an average of many seconds or even a few minutes to obtain reasonable results. Portanto, Raman based systems are only suitable for measuring slowly changing temperatures.

Data collection, processamento de sinal, e visualização

Due to the large amount of data generated by distributed acoustic sensing systems, it is crucial to have a strategy for management, processamento, and data visualization. These systems collect data at speeds above 10 Khz at up to 20 pontos de detecção. This is equivalent to the rate at which terabyte drives can be filled within a few days.

Geralmente, the inquiry unit is connected to the processing unit (industrial PC or server) that manages data storage and processing. Geralmente, there is a scrolling buffer used to store raw data because there is very little content stored beyond this.

The processing unit is programmed using a series of intelligent algorithms to interpret raw data and analyze whether it matches pre-defined events, such as intrusion events or pipeline leaks. The fiber optic sensing cable will be divided into multiple areas, where specific selected algorithms will be selected and alerts will be assigned within each area.

There are many ways to visualize these events. One approach is to use DTS specific visualization software, such as displaying the path of optical fibers based on site maps or charts, and if there are events, it will highlight the location of the events and display alarms. Another approach is for the DAS software interface to be integrated with existing SCADA, controlar, or security software packages. Nesse caso, the event will highlight the software of the parties involved in 3.

DAS measurement principle:

Please add a link to describe that DAS is a distributed fiber optic sensor based on coherent Rayleigh scattering. It utilizes the sensitivity of optical fibers to sound (vibração). When external vibrations act on the sensing optical fiber, due to the elastic optical effect, the refractive index and length of the optical fiber will undergo slight changes, resulting in a phase change of the transmitted signal inside the optical fiber and a change in light intensity.

The phase change caused by sound waves is very small, so DAS systems usually use highly coherent pulse light sources. Interference occurs between Rayleigh scattering signals within the pulse width area. When external vibration causes a phase change, the intensity of the coherent Rayleigh scattering signal at that point will change. By detecting the intensity change of the Rayleigh scattering light signal before and after vibration (differential signal), vibration event detection can be achieved, and multiple vibration events can be accurately located simultaneously.

DAS technology advantages:

Medição distribuída contínua de temperatura e vibração sem pontos cegos de medição

Detecção simultânea e localização precisa de múltiplos eventos

Fiber optic is a sensor that combines transmission and sensing

60 quilômetros de distância de medição ultra longa, informações de medição ricas

Velocidade de resposta rápida, alarme dentro 1 segundo

Transmissão de sinal óptico, completamente isolado eletricamente, resistente a interferência eletromagnética

Segurança intrínseca, adequado para operação de longo prazo em ambientes inflamáveis e explosivos

Medição estável e confiável com baixa taxa de alarmes falsos

Longa vida útil das fibras ópticas, até 30 anos sem manutenção

DAS performance characteristics:

Longa distância de temperatura: 50quilômetros

Tempo de resposta rápido: típico 1 segundo

Alta precisão de posicionamento: 2-50eu

Alta sensibilidade: pode perceber vibrações dentro de 40 m ao redor do cabo óptico

Monitoramento simultâneo de vibração e temperatura

Função de monitoramento on-line para falhas de fibra óptica

Perceiving all things is an important technological support for building a smart earth, smart city, and smart ocean. Distributed Fiber Optic Acoustic Sensing (O) technology is a new type of sensing technology that can achieve continuous distributed detection of vibration and sound fields. It utilizes the highly sensitive characteristics of coherent Rayleigh scattering induced by narrow linewidth single frequency laser in optical fibers, combined with the principle of reflectometer, to perceive environmental vibration and sound field information interacting with optical fibers over long distances and with high spatiotemporal accuracy. This unique information perception ability has attracted widespread attention from both academia and industry for DAS technology. The performance of DAS technology is constantly improving, and its applications are developing rapidly. It has demonstrated its unique technological advantages and potential in perimeter intrusion detection, online monitoring of railway safety, geophysical exploration, and other areas.

Devido às suas vantagens únicas, O DAS atraiu cada vez mais especialistas de diversas áreas em busca de avanços no setor, ao mesmo tempo que coloca exigências crescentes na melhoria da tecnologia DAS.

Depois de mais de uma década de desenvolvimento, O DAS desempenhou um papel insubstituível em vários campos, especialmente nos cenários de aplicação de longa distância, em grande escala, e detecção densa espaçotemporal, incluindo segurança perimetral, transporte, geophysical exploration, monitoramento de saúde estrutural, e outros campos. Os pesquisadores também estão melhorando continuamente a tecnologia DAS para atender às necessidades de aplicações personalizadas de vários campos.

No campo da segurança perimetral, em comparação com métodos convencionais, DAS tem vantagens como forte adaptabilidade ambiental, alta ocultação, grande faixa de monitoramento, e pontos cegos distribuídos. No entanto, how to determine what kind of disturbance and intrusion occurred along the fiber optic cable based on the large number of complex signals detected by DAS is a technical challenge.
In the field of railway transportation, DAS technology uses passive optical fibers as sensing and transmission devices, which can achieve spatial continuous sensing of disturbance signals along the fiber optic line. It has the characteristics of anti electromagnetic interference, long-distance distributed measurement, low cost per unit distance, and no need for on-site power supply. It can effectively compensate for the shortcomings of existing point electromagnetic sensing technology, meet the application needs of railway transportation, and can be quickly integrated into existing railway lines. It has been widely applied.

A exploração de recursos de petróleo e gás também é uma aplicação importante da tecnologia DAS. A tecnologia convencional de exploração de recursos de petróleo e gás utiliza detectores eletrônicos pontuais, que têm desvantagens como baixa eficiência de implantação e longo tempo experimental em grande escala. DAS usa fibras ópticas de comunicação convencionais como componentes de sensores, que são de baixo custo e podem desempenhar um papel durante todo o ciclo de vida da perfuração, conclusão, produção, etc., com vantagens significativas.
Além disso, devido ao pequeno tamanho e peso leve das fibras ópticas, eles são fáceis de incorporar em estruturas como materiais compósitos aeroespaciais, materiais de construção, meio de solo, etc.. O DAS pode obter facilmente sinais de emissão acústica dentro dos materiais, alcançar monitoramento on-line permanente de materiais e estruturas.

Tendências e desafios de desenvolvimento futuro

DAS technology has been continuously maturing, the application market is expanding, and the prospects are thriving. Recentemente, foreign scholars have proposed using existing underground communication optical fibers to build a large-scale monitoring network for geological analysis and major natural disaster (earthquake) detecção. This development direction can tap into the advantages of DAS’s large-scale spatial continuous perception, reactivate all redundant communication fiber optic resources underground worldwide, and has very high market value and development potential.
Although DAS technology has made significant progress, it is not yet fully mature and there are still important technical bottlenecks that need to be addressed, mainly including sensitivity improvement, multi-dimensional detection, and new data processing paradigms.
The sensitivity of DAS technology is relatively high compared to distributed sensing technology. No entanto, compared to conventional point sensing technology, there is still a significant gap. To apply DAS technology on a large scale, it is necessary to significantly improve the sensitivity of this technology, making it close to the level of existing point sensing devices, in order to truly replace existing technological means in various application fields.
Ao mesmo tempo, the existing detection capability of DAS is still limited by the one-dimensional axial structure of optical fibers, and it is difficult to achieve three-dimensional positioning of disturbance sources and multi-component detection of signals, which to some extent limits the technical performance and application scope of DAS. Distributed 2D/3D positioning detection and drone countermeasures based on images

Além disso, a longa distância, spatially dense sampling, and time-domain dense sampling features of DAS generate a huge amount of sensing data. How to convert the huge amount of raw data into useful sensing signals in real time requires the development of new data processing methods and algorithms.

Resumindo, DAS technology provides a revolutionary technological means for the perception of the physical world, which is of great significance for promoting scientific research and the intelligent development of human society.