Suo Wang Wenbin Baojunshi Bin Liu Street
(Institute of Earth Environment Computing Engineering, Department of Earth Sciences, Nanjing University, 2 10093)
BOTDR is a new type of distributed optical fiber sensing monitoring technology, which has been paid more and more attention by engineering circles because of its characteristics of distribution, high precision, long-distance, real-time and long-distance control. Because the monitoring is distributed, the obtained data has an important correlation with the geographical location. Combined with the specific problems encountered in engineering practice, a set of distributed optical fiber sensing monitoring system for large-scale projects based on GIS is developed. This paper focuses on the design requirements of the system, including design objectives, technical framework and characteristic functions. Based on a tunnel BOTDR monitoring project, a set of corresponding monitoring data management system is developed, which realizes the functions of collecting and managing engineering monitoring data, visualizing monitoring results, and comparing and querying monitoring information. It is a multifunctional management system integrating intelligent analysis and decision management.
BOTDR； GIS； Distributed optical fiber sensor; observation system
1 Introduction
Optical fiber sensing technology has been paid more and more attention by engineers and researchers because of its good durability, corrosion resistance, electromagnetic interference resistance and long-term work in harsh environment [3]. As a new distributed sensing technology, Brillouin Optical Time Domain Reflectometer (BOTDR) is gradually recognized by the engineering community. Japan, Canada, Switzerland and other countries have successfully applied this technology to the monitoring of dams, piles, slopes and dams [3]. Since 200 1 Nanjing University Institute of Earth Environment Computing Engineering introduced this technology from Japan for the first time, China has carried out a lot of indoor and outdoor experimental research, successfully completed a number of engineering projects and achieved a series of important research results [4-7].
In practical application, the monitoring results provided by BOTDR have some defects, such as poor visualization effect, difficult data registration and spatial positioning, and weak comprehensive management function. It is difficult for engineers and technicians without systematic training to understand the monitoring results of BOTDR, and the post-processing of the results is also very complicated. Aiming at the shortage of data analysis and management in the field of distributed optical fiber sensing monitoring in large-scale projects, a set of feasible solutions is put forward, and an application system is designed and developed with specific engineering examples. Practice shows that the system can well realize the functions of monitoring data collection and management, visual display of monitoring results and comparative query of monitoring information.
Step 2 ask questions
2. The monitoring principle of1BOTDR [1]
When laser propagates in optical fiber, the interaction between light wave and optical phonon will produce Brillouin scattering light. When the ambient temperature changes little (t ≤ 5), Brillouin optical frequency drift (vB) is directly proportional to the strain (ε) on the optical fiber, and the relationship is shown as follows: in the formula, υB(ε) represents Brillouin frequency drift when the optical fiber is subjected to ε strain; υB(0) represents Brillouin frequency drift when the optical fiber is unstrained; Is the proportional coefficient, about 0.5GHz；; ε is the actual strain of the optical fiber.
Essays on Geological Disaster Investigation and Monitoring Techniques and Methods
In order to obtain the strain information distributed along the optical fiber, it is only necessary to measure the change of Brillouin frequency shift along the optical fiber, and the point along the optical fiber with the length z from the light source can be obtained by the following formula:
Essays on Geological Disaster Investigation and Monitoring Techniques and Methods
Where: c is the speed of light, n is the refractive index of optical fiber, and t is the time from laser emission to Brillouin scattering light reception.
The monitoring principle is shown in figure 1.
Figure 1 BOTDR strain monitoring schematic diagram
2.2 BOTDR problems in performance results
In practical engineering applications, according to different engineering situations, different bonding methods can be used to bond the sensing optical fiber to the surface of the structure (or material) to be monitored, so as to obtain the radial strain distribution information of the bonded structure (or material) along the optical fiber. However, the monitoring results provided by BOTDR have the following defects:
(1) Defects of integrated management of massive data. The monitoring data provided by BOTDR is the strain information of each point along the radial direction of optical fiber (the distance between points is related to the distance resolution of the instrument), and the strain information of these points is given in the form of data points, which makes the original data numerous and complicated.
(2) Data registration between actual mileage and monitoring results. In the actual laying process of distributed optical fiber sensors, some redundant optical fibers are often reserved for positioning needs. In order to match the measured strain with the actual optical fiber mileage, the actual mileage from the strain site to the optical fiber light source must be obtained, and the monitoring mileage provided by BOTRD is the actual length of the optical fiber (including the redundant part), not the actual mileage of the project, that is to say, there is a data registration problem between the monitoring result and the actual mileage.
(3) The intuitive performance of monitoring results is not good. The original monitoring system of BOTDR does not provide threshold setting function, that is, for a specific project, the threshold must be set artificially to find abnormal strain information.
(4) There are many factors that affect the measured data. The monitoring results of BDTOR are measured under the influence of many factors, such as temperature, and the reliability of unprocessed measurement data is poor.
(5) Lack of monitoring data of end users. The monitoring result of BOTDR is a pure text file, which has not been registered and processed. These data are not for end users, but for researchers with BOTDR operation experience, which means that it is difficult for engineers and technicians without professional training to understand the original results of BOTDR.
Design of distributed optical fiber sensing monitoring system for large-scale projects based on GIS
3. 1 system design objectives
In view of the above problems, the distributed optical fiber sensing monitoring system for large-scale projects based on GIS should follow the following overall design objectives:
(1) Complete the daily health diagnosis of the monitored project and analyze the safety of the project. Taking strain analysis as the core, an engineering safety assessment system is established to complete the tasks of data storage and update, query and search, intelligent assessment, statistical analysis, analogy discrimination and drawing and tabulation, which affect planning, management, decision-making and scientific research, and improve the quality and efficiency of engineering management.
(2) Using the data provided by BOTDR, after systematic processing, and cooperating with the field investigation data of the project, the monitoring work for the project quality is completed. The safety of the project is monitored by horizontal and vertical analogy, that is, the data fed back by different optical fibers and the data tested by the same optical fiber at different times are analyzed by analogy, and the reliable results of the project are obtained.
3.2 System technical framework
Combining with the current development trend of GIS and considering the operability of engineering practice, a management system with component GIS as the core is developed under the environment of Visual Basic 6.0 by systematically applying Mapob-Objects provided by ESRI. The technical framework of the system is shown in Figure 2:
Fig. 2 System technical framework diagram
It can be intuitively seen from the technical framework in Figure 2 that the system design is guided by the needs of different users, and the system functions and working modes are constantly updated and improved through information feedback during the development process. Based on the basic geography and attribute database, the system extracts spatial data by the development of GIS, realizes the registration and visual representation of monitoring data by combining with the optical fiber monitoring database, realizes scientific decision-making by constantly updating and perfecting the management decision-making database, and constructs a multifunctional system integrating basic functions, intelligent analysis and decision management.
3.3 Functions and characteristics of the system
The distributed optical fiber sensing monitoring system for large-scale projects based on GIS basically realizes the functions shown in Figure 3.
As can be seen from Figure 3, the system can basically solve the collection and management of engineering monitoring data, visual display of monitoring results and intelligent analysis of monitoring results. It is a multifunctional management and intelligent analysis system with engineering application as the goal and monitoring results as the core.
(1) layer control: the system loads multiple layers (ESRI's shape file, AutoCAD's DXF file or image file JPG, BMP, GIF, TIF, etc. ). When using, users can control whether the layer is visible, the color of primitives, the visualization range, the order of layers, and so on. Through layers, it is easy to browse specific layers.
Figure 3 Functions and features of the system
(2) View control: The system provides basic functions such as image zooming-in, global display, local display and roaming.
(3) Dynamic labeling: The system realizes dynamic tracking labeling at any position in space. Users can get the attribute information of the mouse position at any time after clicking the mouse.
(4) Data maintenance: users can choose two different ways to query, retrieve and change data, and provide perfect ways to query, retrieve and change data from graphics to attributes and from attributes to graphics.
(5) Drawing function: the system provides self-help drawing mode, users can create new layers or draw their own graphics on the original image according to their own ideas and requirements, and add attributes to the data according to the attribute table provided by the program.
(6) Element selection: the system can identify the selected elements in the diagram, pick up objects through lines, rectangles, regions, polygons and circles, and display the attribute data of the picked-up elements. When the optical fiber at a specific position is selected, the optical fiber flashes three times in response to the optical fiber selected by the user.
In addition to the above functions, according to the engineering characteristics of distributed optical fiber monitoring, this system also has the following characteristics:
(1) data analysis: the system provides data analysis function by drawing thematic strain curves. Through the measured data of BOTDR, the thematic map of optical fiber strain curve is drawn, and the strain curves of different colors are set according to different thresholds.
(2) Data registration: between the measured data and the actual engineering mileage, according to the characteristic data information (optical fiber positioning information) of the actual engineering optical fiber laying, the system provides an accurate registration module with small error and strong applicability.
(3) Legend display: the system provides a unique legend to facilitate project management. For example, in practical engineering, five optical fibers are laid on different walls. Two-dimensional schematic diagram can be used to show and draw different legends to distinguish different optical fibers laid on different walls.
(4) Comparative query: The system provides a comparative query mode from the main interface of system operation to the interface of strain curve drawing, and users can choose to query the results from graph to curve or from curve to graph, which greatly improves the quality and efficiency of engineering monitoring.
4 engineering application examples
4. 1 project overview
A tunnel project is a lake tunnel with a total length of about 2.56km, in which the lake tunnel is about 1.66km long, and it is a two-way six-lane three-box structure, in which the left and right boxes are carriageways, and the middle boxes are pipe corridors and maintenance passages, with a clear width of 3 m, a tunnel design width of about 32m, a clearance height of 4.5m and a design speed of 60 km/h. ..
In July 2002, after repeated investigation and demonstration, the tunnel engineering headquarters decided to use BOTDR technology to monitor the overall deformation of the tunnel. From June 2002 to February 2002, 165438+, the project team completed the laying of sensing optical fiber, as shown in Figure 4, and monitored the tunnel deformation in stages. From October to April, 2003/KLOC-0, the construction monitoring stage is the routine monitoring stage from May to September, 2003. In the construction monitoring stage, the influence of later construction on tunnel deformation and the deformation of tunnel box joints are mainly monitored, and the monitoring frequency is 2 days/time. In the routine monitoring stage, the tunnel stability is mainly monitored under the condition of traffic, and the monitoring frequency is 3 ~ 5 times/week.
Fig. 4 General layout of optical fiber in tunnel.
4.2 System Realization of Monitoring Data Management for Tunnel Engineering
4.2. 1 data preparation
The basic data of the system include construction area map, tunnel information, optical fiber laying information and optical fiber monitoring data. These four types of data include both spatial information data and attribute data, which are the basis of system data structure and the premise of system data analysis and management.
(1) Building area map. It mainly provides basic information about the tunnel and its surrounding environment, which is used to determine the construction geographic information and construction route. It provides a standard for drawing two-dimensional schematic diagram of tunnel.
(2) Tunnel information. It mainly provides longitudinal and transverse section information of the tunnel. Cross-sectional information is used to understand the mileage and direction of optical fiber laying, while longitudinal information is mainly used to master the specific construction operation surface, which is the data basis for accurately drawing the two-dimensional schematic diagram of the tunnel.
(3) Optical fiber laying information. It mainly provides laying information of sensing optical fiber. The five sensor optical fibers to be laid are located on different walls of the South Tunnel and the North Tunnel, and the actual laying length of each optical fiber is bound to have an error with the engineering mileage. By understanding the optical fiber positioning information in the laying process, it provides the data foundation for the data registration module.
(4) Optical fiber monitoring data. Mainly referring to the measured strain data of BOTDR, these measured data will get the accurate strain information of different positions of the tunnel after data registration, threshold setting and other system conversion processing.
System workflow
Data management and analysis is the core part of the system, and it is also an important link to obtain accurate engineering monitoring information. Data management and analysis are mainly realized through the following processes:
Step 1: data preparation
Store the measured BOTDR data as * in the specified location. Txt file for data processing and calling.
Step 2: Select optical fiber.
Among the five optical fibers laid, click the required monitoring optical fiber in the main operation interface to complete the selection of the required optical fiber. Click on the selected optical fiber, and the corresponding series will be called in the background.
Step 3: Select the series.
The so-called series refers to the strain information and data registration information of different optical fibers monitored at different times. Selection series operations include transmitting monitoring data, selecting data registration, setting tunnel deformation threshold, etc.
Step 4: Strain analysis
After a series of choices, choose to draw curves. After data registration, the system will draw the overall strain analysis diagram of the tunnel in a new window.
In addition to the above-mentioned main data management and analysis functions, the system also has the function of subsection management and analysis, that is, by setting the starting point and ending point of the required monitoring section to manage and analyze local data. In addition, the system also provides a comparative query method from graph to curve (or curve to graph). After selecting the menu item from graph to curve (or curve to graph), graph and curve correspond perfectly, and the threshold setting function is provided to realize automatic early warning and avoid human interference. Figure 5-7 shows the operation interface of system data and management functions, in which Figure 5 is the data analysis interface, Figure 6 is the selection series interface, and Figure 7 is the tunnel strain analysis curve interface.
Figure 5 Data Analysis Interface Diagram
Figure 6 Selection Series Interface
Fig. 7 Interface of Tunnel Strain Analysis Curve
5 conclusion
To sum up, applying GIS to manage distributed optical fiber monitoring projects can achieve efficient management of massive data. GIS has become the first choice for engineering management because of its unique data management, query, retrieval and analysis mode. Its hierarchical management of massive data, visual representation of data results, two-way query and end-user orientation show its ideal engineering management ability. Specifically, the system has the following advantages:
(1) system improves the comprehensive management mode of massive data in BOTDR original system, and the results are more clear and intuitive.
(2) The system is equipped with modules such as data registration and threshold management, and the monitoring results can be directly applied, thus avoiding the error of manual discrimination and improving the work efficiency.
(3) The system adopts visual display, facing the end users, and there is no need to systematically train specific engineering monitoring personnel.
(4) The system has realized the collection and management of engineering monitoring data, visual display of monitoring results, comparative inquiry of monitoring information and other functions. It is a multifunctional management system integrating intelligent analysis and decision management.
Taking a specific project as an example, the system has the advantages of being more scientific, efficient, intuitive and convenient, reducing the late human interference of BOTDR monitoring results, making the test results more objective and accurate, which is conducive to scientific management and improving efficiency.
refer to
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