Island reef geological disaster monitoring method and system based on distributed optical fiber acoustic sensing

Abstract

The application discloses an island geological disaster monitoring method and system based on distributed optical fiber acoustic sensing, which formulates a suitable optical cable laying scheme for a target island, improves the coupling degree of the optical cable and the surrounding medium, and then senses, stores and processes vibration signals according to the characteristics of DAS monitoring of the island, extracts the land part characteristic signals, the underwater land slope part characteristic signals and the deep sea part characteristic signals, which can be used for monitoring and researching island geological activities, geological disasters and structural stability, and can also be used for island underground space development, marine environment monitoring, human activity identification and other application fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distributed optical fiber vibration detection, and particularly relates to an island geological disaster monitoring method and system based on distributed optical fiber acoustic sensing. BACKGROUND

[0002] The underground structure of an island is complex and variable, with significant lateral differences, and potential underground cave, fracture and landslide geological structure hidden dangers, once a geological disaster occurs, it will cause serious damage to the infrastructure, life and property of residents and the ecological environment on the island. Therefore, effectively monitoring the geological activity of the island and preventing the geological disaster of the island is an important guarantee for the sustainable development of the development and utilization of island land resources and island construction.

[0003] At present, the main investigation means for island geological disaster hidden dangers is to carry out reflection seismic or wide-angle seismic exploration in the sea area around the island, or to choose to carry out timed and fixed point observation on the reef to obtain the internal structure of the island and its changes. However, the water depth of the island area changes dramatically, and there is a cliff-like change from several meters of water depth in the island inner platform to several kilometers of water depth in the outer periphery of the island. In the shallow water environment of the island inner platform, most investigation ships and exploration equipment cannot operate safely, so the geological structure and geophysical investigation of the island are mainly dispersed in the deep water area outside the island body. This makes the existing technical system which mainly uses reflection seismic and wide-angle seismic exploration as the main means unable to effectively obtain high-precision perspective images of the shallow underground space structure of the island, and unable to effectively monitor the geological activity of the island. The timed and fixed point observation method can only be limited to periodic observation on specific points of the island, and the time and spatial density of monitoring is very limited, and cannot form a systematic understanding of the geological activity of the island. In summary, although the existing related technical means is very helpful for understanding the geological structure of the island, the time density and spatial density of observation are greatly insufficient, and the resolution is very limited, which cannot provide real-time monitoring for the change of the geological activity of the island, so that we cannot realize immediate and systematic cognition of the potential geological disaster hidden dangers in the island body.

[0004] Distributed Acoustic Sensing (DAS) is a new technology with great potential in the application of optical cable in seismic and environmental monitoring in recent years. It can effectively convert the optical cable into a dense array of seismic sensors, and then use the pulse signal released by the DAS host to continuously detect the stress and strain caused by the interaction between the external vibration signal and the optical cable, so as to carry out remote, dense and real-time observation of the external vibration wave field. Compared with other geophysical exploration methods, DAS technology can use the laid optical cable to carry out continuous long-term observation, has high sensitivity, can provide dense temporal and spatial sampling rate, and has achieved good results in microseismic, regional seismic and teleseismic monitoring. However, although DAS technology is developing rapidly, its applicability to island reefs has not been studied and applied. SUMMARY

[0005] In order to solve the above problems, the present application provides an island reef geological disaster monitoring method and system based on distributed optical fiber acoustic sensing, which mainly solves the problem that the existing distributed acoustic sensing technology is not suitable for island reef stress monitoring.

[0006] To solve the above technical problems, the technical scheme of the present application is as follows:

[0007] The first aspect of the present application provides an island reef geological disaster monitoring method based on distributed optical fiber acoustic sensing, comprising the following steps:

[0008] Formulate an optical cable laying scheme according to the shallow geological conditions of the target island reef, and lay the optical cable according to the optical cable laying scheme;

[0009] The laser injects a laser pulse signal into the optical fiber of the optical cable, the signal processing device receives the returned interference light signal, analyzes the phase change of the Rayleigh backscattering signal in the interference light signal, and calculates the vibration signal through the phase change;

[0010] In the sampling period, the information generated by the laser and the signal processing device is encoded as metadata, the vibration signal is compressed and encoded as a data block, and the metadata and the data block are integrated into vibration data;

[0011] Convert the vibration data into a seismic universal data format, filter and stack the seismic universal data format after noise reduction, input into a machine learning model, and perform feature signal identification to extract land part feature signal, underwater land slope part feature signal, and deep sea part feature signal;

[0012] Output the analysis model of the land part characteristic signal, the underwater continental slope part characteristic signal and the deep sea part characteristic signal, and output a disaster prediction value.

[0013] In some embodiments, the strategy of the optical cable laying scheme is that the optical cable is laid in a direct-buried manner in the land environment of the target island, the optical cable is laid in a barge method in the slope wall of the underwater continental slope of the target island, and the optical cable is laid in a gravity sinking method in the deep sea environment of the target island.

[0014] In some embodiments, the direct-buried manner is specifically that a trench is dug in the land environment, a square groove is arranged at the bottom of the trench, a layer of filler is pre-laid in the square groove, and then the optical cable is laid, a layer of filler is filled in the square groove after the optical cable is laid, rigid plate is laid on the top of the square groove after the filler is compacted, and finally the trench is backfilled and rammed.

[0015] In some embodiments, the sampling rate of the interference light signal is dynamically adjusted according to different observation targets and research purposes.

[0016] In some embodiments, invalid data in the DAS data record is eliminated in the process of converting the vibration data into the seismic general data format.

[0017] The second aspect of the present application provides an island geological disaster monitoring system based on distributed optical fiber acoustic sensing, comprising:

[0018] A laying scheme preparation module is configured to prepare an optical cable laying scheme according to the shallow geological conditions of a target island, and lay an optical cable according to the optical cable laying scheme.

[0019] A vibration signal generation module is configured to inject a laser pulse signal into an optical fiber of the optical cable by a laser, receive a returned interference light signal by a signal processing device, analyze a phase change of Rayleigh backscattering signals in the interference light signal, and generate a vibration signal by calculating the phase change.

[0020] A data storage module is configured to encode information generated by the laser and the signal processing device as metadata, compress and encode the vibration signal as a data block, and integrate the metadata and the data block as vibration data within a sampling period.

[0021] A data analysis module is configured to convert the vibration data into a seismic general data format, input the seismic general data format into a machine learning model after filtering, superposition and noise reduction, and identify characteristic signals, extract land part characteristic signals, underwater continental slope part characteristic signals and deep sea part characteristic signals.

[0022] A disaster prediction module is configured to output the land portion characteristic signal, the underwater land slope portion characteristic signal, and the deep sea portion characteristic signal to an analysis model, and output a disaster prediction value.

[0023] In some embodiments, the strategy for laying the optical cable is as follows: the optical cable is laid in a direct-buried manner in the land environment of the target island reef, the optical cable is laid in a barge method by digging a trench in the slope wall of the underwater land slope environment of the target island reef, and the optical cable is laid in a gravity sinking method in the deep sea environment of the target island reef.

[0024] In some embodiments, the direct-buried manner is as follows: a trench is dug in the land environment, a square groove is arranged at the bottom of the trench, a layer of filler is pre-laid in the square groove, and then the optical cable is laid, a layer of filler is filled in the square groove after the optical cable is laid, rigid plate is laid on the top of the square groove after the filler is compacted, and finally the trench is backfilled and tamped.

[0025] In some embodiments, the sampling rate of the interference light signal is dynamically adjusted according to different observation targets and research purposes.

[0026] In some embodiments, invalid data in the DAS data record is eliminated in the process of converting the vibration data into the seismic universal data format.

[0027] The beneficial effects of the present application are as follows: by formulating a suitable optical cable laying scheme for a target island reef, the coupling degree of the optical cable and the surrounding medium is improved, then the vibration signal is perceived, stored and processed according to the characteristics of DAS monitoring of the island reef, and the land portion characteristic signal, the underwater land slope portion characteristic signal, and the deep sea portion characteristic signal are extracted, which can be used for monitoring and research of island reef geological activities, geological disasters and structural stability, and can also be used in many application fields such as island reef underground space development, marine environment monitoring, and human activity identification. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A flowchart of an island reef geological disaster monitoring method based on distributed optical fiber acoustic sensing according to an embodiment of the present application is disclosed;

[0029] Figure 2 A schematic diagram of an island reef optical cable laying method according to the present application is disclosed;

[0030] Figure 3 A schematic diagram of an island reef optical cable laying method in a land environment according to the present application is disclosed;

[0031] Figure 4 A function diagram of optical phase change according to the present application is disclosed;

[0032] Figure 5 The structural schematic diagram of the island geological disaster monitoring system based on distributed optical fiber acoustic sensing disclosed in Embodiment Two of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present application more clear and explicit, the content of the present application will be further described in detail below in combination with the drawings and specific embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that only the parts related to the present application are shown in the drawings for the convenience of description, but not all the contents.

[0034] Embodiment One

[0035] The present embodiment proposes an island geological disaster monitoring method based on distributed optical fiber acoustic sensing. The method mainly formulates a suitable optical cable laying scheme for the target island, improves the coupling degree of the optical cable and the surrounding medium, and then senses, stores and processes the vibration signals according to the characteristics of the island monitoring by DAS, extracts the land part feature signals, underwater land slope part feature signals and deep sea part feature signals, which can be used for monitoring and researching the island geological activities, geological disasters and structural stability, and can also be used in many application fields such as island underground space development, marine environment monitoring, human activity identification, etc. As shown in the figure, the method includes the following steps: Figure 1

[0036] 101. Formulate an optical cable laying scheme according to the shallow geological conditions of the target island, and lay the optical cable according to the optical cable laying scheme.

[0037] The main function of the traditional communication optical cable is data transmission, so under the premise of ensuring the safety of the optical cable, many laying methods such as overhead, pipeline, direct burial, underwater and wall can be selected, while the optical cable for distributed optical fiber sensing is designed to sense the vibration information outside the optical cable itself, which requires that the optical cable and the surrounding medium must have good contact coupling. Therefore, the optical cable for distributed optical fiber sensing needs to be laid in a direct burial manner. The geological carrier to which the present application will be applied, i.e. the island laying environment, is more complex, including land, land slope and deep sea laying environments, which requires designing different laying methods according to different laying environments. Therefore, the strategy for formulating the optical cable laying scheme is as shown in the figure, i.e. the land environment of the target island is laid in a direct burial manner, the underwater land slope environment of the target island is laid by the barge method to dig a groove on the slope wall of the underwater land slope, and the deep sea environment of the target island is laid by the gravity sinking method. Figure 2

[0038] Among them, it should be noted that the direct burial manner is as shown in the figure, i.e. the optical cable is laid in a direct burial manner on the land of the target island, the underwater land slope environment of the target island is laid by the barge method to dig a groove on the slope wall of the underwater land slope, and the deep sea environment of the target island is laid by the gravity sinking method. Figure 3 ​​As shown, in the land environment, a trench is dug, and the buried depth is 30-50 cm. The bottom of the trench is provided with a square groove, which can be paved with concave cement bricks or formed by cement hardening around. After a layer of filler is pre-paved in the square groove, the optical cable 1 is paved, and then a 10 cm layer of filler 2 is paved to fill the square groove. After the filler 2 is compacted, a rigid plate 3 is paved on the top of the square groove, and finally the trench is backfilled and rammed. In some embodiments, warning signs can also be provided directly above the direct-buried path. The filler 2 can be selected from thin soil or sand, and the rigid plate 3 can be selected from red bricks, which are common building materials and easy to obtain. Such a square groove design is not only to protect the safety of the optical cable and ensure the contact coupling between the optical cable 1 and the surrounding medium, but also to play a certain heat insulation role, so that the environmental temperature change of the optical cable 1 will not be too large. When the optical cable 1 crosses the roads and streets of the target island reef, it is passed through by installing a protective pipe 4.

[0039] When laying the underwater optical cable on the continental slope with a shallow water depth (<100 m), a barge method is used to dig a trench on the slope wall for laying. When in a deep water environment with a large water depth (more than 100 m), a gravity sinking method is directly used to lay the optical cable on the seabed. In order to ensure the safety and practicality of the optical cable, the optical cable is a filled armored optical cable.

[0040] 102、The laser injects a laser pulse signal into the optical fiber of the optical cable, and the signal processing device receives the returned interference light signal, analyzes the phase change of the Rayleigh backscattering signal in the interference light signal, and calculates the vibration signal through the phase change.

[0041] The distributed optical fiber sensing technology uses the optical fiber itself as a vibration sensor, and measures the external stress and strain distributed along the entire optical cable by using the phase change of the optical signal. A commonly used technology is to use an interrogator unit (i.e. a laser) to repeatedly inject a laser pulse into the optical fiber, and then analyze the phase change of the Rayleigh backscattering signal, and determine the phase change section distance by calculating the propagation time of the light in the optical fiber. The coherent light time domain reflection method converts the backscattering in a continuous time period into a group of independent signals returned from the continuous optical fiber section, and the length is called the gauge length. The gauge length is the spatial increment of the optical fiber corresponding to each sampling signal, which is usually about 1 to 40 meters long, and it determines the spatial resolution of the DAS. The DAS interrogator unit measures the strain by measuring the optical phase change between the adjacent gauge length optical fibers at a certain time (a certain pulse), which is also called the fast axis measurement, or measures the strain rate by the phase change of the mixed signal returned in the same gauge length by two pulses, which is also called the slow axis measurement, as shown. Figure 4 The above-mentioned laser and signal processing device can be part of a distributed optical fiber acoustic sensing host, or two independent devices.

[0042] 103. During the sampling period, the information generated by the laser and signal processing device is encoded as metadata, the vibration signal is compressed and encoded into data blocks, and the metadata and data blocks are integrated into vibration data.

[0043] This invention utilizes DAS technology to conduct high-sampling, long-period observations of island and reef dynamics. This inevitably results in experimental data volumes far exceeding those of traditional seismic experimental data, growing exponentially. How to efficiently store, access, archive, and analyze this observation data will become a challenging problem. The main format of the vibration data in this invention consists of two parts: a header section and data blocks. The header section stores metadata during DAS data recording, mainly including instrument performance indicators, location, sampling rate, data acquisition start time, number of sensors, and spacing, among other basic data elements. The data blocks require a specially designed encoding method to significantly reduce data storage space and improve the efficiency of reading and calculating large volumes of data.

[0044] To adapt to different observation targets and research objectives, the sampling rate of the interferometric optical signal is dynamically adjusted. Based on the spectral characteristics of the target signal, frequency-division observation and segmented storage are employed for recording and storage. Specifically, the system data sampling rate and the band of the data to be stored are dynamically adjusted according to the frequency band information of the observation target. For example, when the observation target is a natural earthquake signal, the sampling rate can be adjusted to 30-50%, which greatly reduces storage space requirements and improves processing and analysis efficiency in later stages, saving time costs. When conducting artificial source signal excitation and experimental research, the dominant frequency of the artificial source signal generally varies depending on the source type; the sampling rate can be dynamically adjusted according to changes in experimental and research objectives. If we are conducting analysis and research on environmental noise signals, the sampling rate can be increased to the maximum level to acquire as much environmental information as possible, facilitating detailed analysis, identification, extraction, and comparative research of environmental information in different frequency bands. Of course, in practical work, it is also necessary to dynamically design data sampling modes according to the different observation and experimental targets and changing characteristics to achieve the implementation of special observations and research. This targeted storage based on research objectives and different spectral characteristics of effective signals can effectively improve the problem of storing large amounts of data in distributed fiber optic sensing, and also improve the efficiency of subsequent signal processing and analysis.

[0045] 104. Convert the vibration data into a general seismic data format. After filtering and denoising the general seismic data format, input it into the machine learning model and perform feature signal recognition to extract feature signals from the land area, the underwater slope, and the deep sea.

[0046] In addition to high density of space-time sampling rate, DAS data recording has several other special features. First of all, it is a single-component sensing feature. Land seismic instruments usually provide three-component recording, and ocean bottom seismic instruments can provide four-component recording, while DAS usually only has single-component direction sensitivity. Secondly, it is a linear array feature. In DAS technology, the optical fiber is not only a signal transmission medium, but also a sensing medium, which limits the sensor to have a linear distribution along the length of the optical fiber. The special nature of the DAS data described above makes it necessary to improve the existing algorithms for conventional seismic data processing methods, such as detecting signals, locating sources, and imaging underground structures using body waves and surface waves, in order to accurately deal with the differences of DAS dynamic linear array recording data. In addition, efficient processing and analysis algorithms for large volume of DAS data become increasingly important. Therefore, in the later data processing stage, the data processing is planned to be carried out according to the following process: (1) Data conversion. Through the development of software programs, the conversion of DAS data recording to the format of traditional seismic data is realized, and the special nature of DAS data recording is fully considered and eliminated in the conversion process, such as eliminating invalid data in DAS data recording in the process of converting vibration data into general seismic data format; at the same time, according to the research purpose and signal requirement, different types of signals can be frequency- and body-converted in the data conversion process. (2) Algorithm improvement. According to the characteristics of DAS data such as high density, single component and linear array, the existing algorithms are improved to realize the applicability of the existing methods and improve the connection and convergence ability between different software platforms and different data processing methods, so as to achieve the generalization of the existing conventional signal processing methods and software for distributed optical fiber sensing signals. (3) Stack and denoising. The spacing between DAS sensors is very small, which can reach the range of 2-10 meters. We can take advantage of the extremely dense multi-channel data characteristics of DAS to reduce the environmental background noise and improve the signal-to-noise ratio of the target signal through adjacent channel stacking, so as to enhance the signal detection, recognition and extraction ability. (4) Machine learning. The high density of space-time sampling rate of DAS data determines that the data recording must contain a variety of signals. It is a time-consuming and labor-intensive project to carry out signal processing and detection and recognition for long-term data recording. Therefore, the data processing process needs to improve the scientificity of the processing flow on the one hand, and actively combine with the latest intelligent processing technology and method of machine learning on the other hand. In the early stage of data processing, different sound source signals in DAS recording are identified, recorded and stored by artificial intelligence, and relevant signal information is actively collected to eliminate false information and store accurate information, classify and integrate, and establish a sound source information library; then the established signal information library is used to carry out targeted machine training to realize machine learning; finally, template matching is used to automatically detect signals and classify, realizing the feature signal recognition and extraction of optical fiber data by artificial intelligence, and improving the processing and analysis ability of distributed optical fiber sensing large volume data.

[0047] 105. Output the characteristic signals of the land area, the characteristic signals of the underwater slope, and the characteristic signals of the deep sea into the analysis model, and output the disaster prediction value.

[0048] Example 2

[0049] A geological hazard monitoring system for islands and reefs based on distributed fiber optic acoustic sensing, such as Figure 5 As shown, it includes:

[0050] The cable laying scheme formulation module 201 is used to formulate a cable laying scheme based on the shallow geological conditions of the target islands and reefs, and to lay the cable according to the cable laying scheme.

[0051] The vibration signal generation module 202 is used to inject laser pulse signals into the optical fiber of the optical cable by the laser, and the signal processing device receives the returned interference light signal, analyzes the phase change of the Rayleigh backscattered signal in the interference light signal, and calculates and generates a vibration signal through the phase change.

[0052] The data storage module 203 is used to encode the information generated by the laser and signal processing device into metadata during the sampling period, and to compress and encode the vibration signal into data blocks, and to integrate the metadata and data blocks into vibration data.

[0053] The data analysis module 204 is used to convert vibration data into a general earthquake data format. After filtering and noise reduction of the general earthquake data format, it is input into the machine learning model and performs feature signal recognition to extract feature signals from the land area, the underwater slope, and the deep sea.

[0054] The disaster prediction module 205 is used to output the characteristic signals of the land area, the characteristic signals of the underwater slope, and the characteristic signals of the deep sea into the analysis model, and output the disaster prediction value.

[0055] The strategy for developing an optical cable laying plan is as follows:

[0056] In the land environment of the target islands and reefs, the optical cable is laid by direct burial. In the underwater land slope environment of the target islands and reefs, the optical cable is laid by digging trenches on the slope wall of the underwater land slope using the barge method. In the deep sea environment of the target islands and reefs, the optical cable is laid by gravity sinking.

[0057] The direct burial method is as follows:

[0058] In a terrestrial environment, a trench is dug, and a square groove is set at the bottom of the trench. A layer of filler is laid in the square groove before the optical cable is laid. After the optical cable is laid, another layer of filler is laid to fill the square groove. After the filler is compacted, a rigid plate is laid on top of the square groove. Finally, the trench is backfilled and compacted.

[0059] The sampling rate of the interference light signal is dynamically adjusted according to different observation targets and research purposes.

[0060] Eliminating invalid data in DAS data records in the process of converting vibration data into seismic universal data format.

[0061] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for monitoring geological disasters of islands based on distributed optical fiber acoustic sensing, characterized in that, The method comprises the following steps: According to the shallow geological conditions of the target island, an optical cable laying scheme is formulated, and the optical cable is laid according to the optical cable laying scheme; The strategy for formulating the optical cable laying scheme is that the optical cable is laid by direct burial in the land environment of the target island, the optical cable is laid by barge method in the trench dug in the slope wall of the underwater slope of the target island, and the optical cable is laid by gravity sinking method in the deep sea environment of the target island; The direct burial method is as follows: a trench is dug in the land environment, a square groove is arranged at the bottom of the trench, a layer of filler is pre-laid in the square groove, and then the optical cable is laid, a layer of filler is filled in the square groove after the optical cable is laid, rigid plate is laid on the top of the square groove after the filler is compacted, and finally the trench is backfilled and rammed; The laser injects a laser pulse signal into the optical fiber of the optical cable, the signal processing device receives the returned interference light signal, analyzes the phase change of the Rayleigh backscattering signal in the interference light signal, and calculates the vibration signal through the phase change; In the sampling period, the information generated by the laser and the signal processing device is encoded as metadata, the vibration signal is compressed and encoded as a data block, and the metadata and the data block are integrated into vibration data; The vibration data is converted into a seismic universal data format, the seismic universal data format is filtered and stacked to reduce noise, input into a machine learning model, and characteristic signals are identified, and the land part characteristic signal, the underwater slope part characteristic signal, and the deep sea part characteristic signal are extracted; The land part characteristic signal, the underwater slope part characteristic signal, and the deep sea part characteristic signal are output to an analysis model, and a disaster prediction value is output; The sampling rate of the interference light signal is dynamically adjusted according to different observation targets and research purposes; In the process of converting the vibration data into the seismic universal data format, invalid data in the DAS data record is eliminated.

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