Monitoring and early warning method of tidal flat strange tide based on distributed optical fiber vibration sensing

Abstract

This invention discloses a method for monitoring and warning of tidal flat tidal waves based on distributed optical fiber vibration sensing. It also provides a method for deploying sensor cables for monitoring tidal flat tidal waves. By obtaining a spatiotemporal distribution waterfall diagram of monitoring signals in the tidal flat area, the invention uses the spatiotemporal distribution waterfall diagram of the tidal flat monitoring signals and the strength of the monitored signals at various sensing distances to set tidal flat warning zones. Different levels of warning lines are then calibrated for these zones, providing an early warning solution for tidal flat tidal waves.

Description

Technical Field

[0001] The invention relates to a method for monitoring and warning of tidal flat freak tides based on distributed optical fiber vibration sensing, and belongs to the technical field of optical fiber sensing. Background Art

[0002] Marine mudflats generally refer to coastal tidal flats, defined as areas below the mean high tide line and above the mean low tide line. Tidal flats are crucial bases for aquaculture and fishery development, and represent a valuable asset for marine development and the development of marine industries. However, operations on these tidal flats often experience "freak tides," a phenomenon characterized by a sudden surge of tidal currents and a significant increase in waves within a short period of time, driven by the combined effects of waves and tidal currents. During high tide, when the tide reaches mid-water, there is a rapid rise in the tidal flat, with the water level rising by nearly 1 meter within 20 minutes. This is precisely when the water begins to flow over the tidal flat aquaculture operation area, and the tidal currents are at their highest. If mudflat workers are not evacuated promptly, they can easily be engulfed by the rapidly rising tides and high currents. These "freak tide" disasters have had a significant impact on local fishery production and coastal engineering activities. Scientifically preventing the hazards caused by "freak tides" has become a key focus for marine observatories and marine disaster research in recent years. At present, research on "strange tides" mainly focuses on the A-GPS-based "strange tide" personnel evacuation command and decision-making system and the theoretical statistical model research on the occurrence mechanism and early warning of "strange tides". There is still a technical gap in the research on how to monitor and warn of "strange tides".

[0003] Distributed vibration sensing systems use narrow-linewidth lasers as their light source and exploit the coherent fading effect between backscattered Rayleigh scattering signals (RBS) to achieve distributed measurement of disturbance signals. When an external disturbance event acts on an optical fiber, the core refractive index and fiber length at the disturbance location change, causing the amplitude and phase of the RBS at that location to change. By analyzing the Rayleigh scattering curves before and after the disturbance event, dynamic disturbance events can be detected. This technology offers high sensitivity and a fast measurement response, enabling long-distance, fully distributed, dynamic monitoring without blind spots. Summary of the Invention

[0004] To address the shortcomings of existing "strange tide" monitoring technology, this paper proposes a monitoring and early warning method for "strange tides on mudflats" based on distributed vibration sensing. First, a method for deploying sensor cables for monitoring "strange tides on mudflats" is provided. By obtaining a waterfall diagram of the spatiotemporal distribution of monitoring signals in the mudflat area, warning zones for "strange tides" are defined, and warning lines of different levels are calibrated within these zones. This provides an early warning solution for "strange tides on mudflats."

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] A tidal flat freak tide monitoring system based on distributed optical fiber vibration sensing includes a distributed vibration sensing system, a sensing cable, and a processor. The sensing cable is laid out in a continuous "∧" pattern in the tidal flat operation area, with one or more cable loops wound around the top corner of each "∧" pattern.

[0007] The head end of the sensing cable is connected to a distributed vibration sensing system to obtain backscattered Rayleigh signals along the sensing cable;

[0008] The processor demodulates the backscattered Rayleigh signal to obtain a spatiotemporal distribution waterfall diagram of the monitoring signal of the tidal flat operation area.

[0009] Furthermore, the coverage of the sensor cable is larger than the mudflat operation area and is buried underground.

[0010] Furthermore, the layout of the sensor cable must meet the following conditions:

[0011] (1) d>D2;

[0012] (2)

[0013] (3) Where d is the layout width of the sensor cable, L is the total length of the sensor cable, θ is half of the “∧”-shaped inner angle, D1 and D2 are the length and width of the mudflat operation area, respectively, and R is the spatial resolution of the distributed vibration sensing system.

[0014] Furthermore, the horizontal axis of the spatiotemporal distribution waterfall diagram of the monitoring signal is distance, and the vertical axis is time; the color mapping is the signal strength, and the brighter the color, the greater the strength.

[0015] A method for monitoring tidal flat freak tides based on distributed optical fiber vibration sensing is described. The method is based on the above-mentioned monitoring device and has the following specific steps:

[0016] Step 1: Lay the sensor cable in a continuous “∧” shape in the mudflat operation area, and wind one or more cable loops around the top corner of each “∧” shape to anchor the sensor cable;

[0017] Step 2: Connect the head end of the sensor cable to the distributed vibration sensing system to obtain the backscattered Rayleigh scattering signal along the sensor cable;

[0018] Step 3: Demodulate the backscattered Rayleigh signal to obtain a spatiotemporal distribution waterfall diagram of the monitoring signal in the mudflat operation area.

[0019] A method for warning of tidal flat tidal waves based on distributed fiber optic vibration sensing specifically involves the following steps: Based on the local tidal flat terrain, tidal velocity, and personnel evacuation plan, combined with the spatiotemporal distribution waterfall diagram of the monitoring signal obtained in step 4, a tidal flat warning zone is set, and different levels of warning lines are calibrated within the tidal flat warning zone. For example, based on the strength of the monitored signals at each sensing distance, the highest warning water level that can ensure the safe evacuation of all personnel when a tidal flat approaches is calibrated as a Level I warning line. That is, when the sensing system detects this Level I warning water level, all personnel must evacuate immediately, otherwise danger will ensue. The water level at the center of the width r1 corresponding to the upper perimeter of the sensor cable 1, where the tidal current or waves just touch the sensor cable 1, is calibrated as a Level II warning line. The water level corresponding to the weak signal, where the tidal current or waves have not yet directly touched the sensor cable 1, is calibrated as a Level III warning line. The amount of early warning can be calibrated based on actual conditions.

[0020] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0021] (1) The distributed vibration sensing-based "tidal flat tidal wave" monitoring and early warning method provided by the present invention combines "tidal flat tidal wave" monitoring with distributed vibration sensing technology, and utilizes the continuous sensing and high sensitivity characteristics of distributed vibration sensing to provide a new, highly sensitive, and fully distributed "tidal flat tidal wave" monitoring method;

[0022] (2) A method for deploying a sensor cable for monitoring “strange tides on mudflats” is provided;

[0023] (3) By obtaining the spatiotemporal distribution waterfall diagram of the mudflat monitoring signal and using the strength of the signal at each sensing distance, the strange tide warning zone is set, and different levels of warning lines are calibrated for the strange tide warning zone, providing an early warning plan for "mudflat strange tides". BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the layout of the "strange tide on mudflats" monitoring sensor cable of the present invention, wherein 1 is the sensor cable, 2 is the cable ring, 3 is the upper width of the sensor cable layout, and 4 is the lower width of the sensor cable layout;

[0025] Figure 2 This is a schematic diagram of the correspondence between the spatiotemporal distribution waterfall diagram results of the tidal flat area monitoring of the present invention and the spatial position of the tidal flat monitoring area. DETAILED DESCRIPTION

[0026] The embodiments of the present invention will be described below with reference to the accompanying drawings.

[0027] The present invention proposes a "tidal flat strange tide" monitoring and early warning method based on distributed vibration sensing. First, a "tidal flat strange tide" monitoring sensor cable layout method is provided. Steps 1 to 2 are performed:

[0028] Step 1: If Figure 1 As shown, the sensor cable 1 is laid out in a continuous "∧" pattern in the mudflat operation area. The coverage area of ​​the sensor cable 1 is larger than the mudflat operation area. Preferably, the sensor cable is buried. Two cable loops with a diameter of approximately 30 cm are wound around the top corners of each "∧" pattern. The loops are anchored in the soil with U-shaped nails and compacted to enhance the coupling between the top corners of the sensor cable 1 and the mudflat, thereby improving monitoring sensitivity.

[0029] It is known that the length D1 of the tidal flat operation area is 3 km and the width D2 is 600 m. According to the layout criteria of the sensor cable 1 in step 2 of the present invention,

[0030] (1) The laying width d of the “∧” type sensor cable 1 is greater than D2;

[0031] (2) Total length of sensor cable 1

[0032] (3)

[0033] Select the layout width of the “∧” type sensor cable 1 as d=650m>D2; select θ=30° as an example, the total length θ=30° satisfies:

[0034] The intersection points of the water level acting on each "∧" type unit cable and the sensing cable 1 are intersection points ① and ② in order. The sensing distance corresponding to each intersection point ① and intersection point ② is r1, and the sensing distance corresponding to the intersection point ① and intersection point ② of two adjacent "∧" type unit cables is r2. The spatial resolution of the distributed vibration sensing system is set to R = 10m. In order to be able to distinguish the water level lines that can be identified by adjacent "∧" types, we have: θ satisfies:

[0035]

[0036] Step 3: Connect the head end of the sensor cable 1 to the distributed vibration sensing system, turn on the monitoring system, and obtain the backscattered Rayleigh signal along the sensor cable 1;

[0037] Step 4: By demodulating the backscattered Rayleigh scattering signal, we can obtain a spatiotemporal distribution waterfall diagram of the monitoring signal in the mudflat area. The horizontal axis is distance, the vertical axis is time, and the color is mapped to the signal intensity. The brighter the color, the greater the intensity. Figure 2As shown in FIG. 1 , a schematic diagram of the corresponding relationship between the spatiotemporal distribution waterfall diagram results of the tidal flat monitoring area according to the present invention and the spatial position of the tidal flat monitoring area is shown. The corresponding sensing distance between the top angles of two adjacent “∧”-shaped sensor cables 1, that is, the upper perimeter of the layout width of the sensor cable 1, and the two adjacent cable loops 2 on the distribution waterfall diagram is: The closer the water level is to the shore, the wider the area of ​​underwater acoustic vibration intensity detected by a single "∧"-shaped unit cable area becomes, that is, r1 increases, and the intensity is greatest at the water level. The center of r1 width corresponds to the spatial location of cable loop 2, where the upper perimeter of the sensor cable 1 is located. As the distance from the water level increases, the signal strength gradually decreases.

[0038] Step 5: Based on the local mudflat conditions, tidal velocity, and evacuation plan, combined with the spatiotemporal distribution waterfall diagram of the monitoring signal obtained in Step 4, a freak tide warning zone is defined and different levels of warning lines are calibrated for the freak tide warning zone. For example, based on the strength of the monitored signals at each sensing distance, the highest warning water level that can ensure the safe evacuation of all personnel during a freak tide is calibrated as the Level I warning line. That is, when the sensing system detects this Level I warning water level, all personnel must evacuate immediately, otherwise danger will occur. The water level at the center of width r1, corresponding to the upper perimeter of the sensor cable 1 installation width, at cable loop 2, is calibrated as the Level II warning line, when the tidal current or waves just touch the sensor cable 1. The water level corresponding to the weak signal, when the tidal current or waves have not yet directly touched the sensor cable 1, is calibrated as the Level III warning line. The amount of early warning can be calibrated based on actual conditions.

[0039] It should be pointed out that the description of the above embodiments is only used to help understand the method of this application and its core idea. For ordinary technicians in this technical field, without departing from the principles of this application, several improvements and modifications can be made to this application, and these improvements and modifications are also within the scope of protection of the claims of this application.

Claims

1. The system for monitoring tidal flats and unusual tides based on distributed optical fiber vibration sensing is characterized by: The monitoring system includes a distributed vibration sensing system, a sensing cable and a processor. The sensing cable is laid out in a continuous "∧" shape in the mudflat operation area, with one or more cable loops wound around the top corner of each "∧" shape. The head end of the sensing cable is connected to a distributed vibration sensing system to obtain backscattered Rayleigh signals along the sensing cable; The processor demodulates the Rayleigh backscatter signal to obtain a spatiotemporal distribution waterfall diagram of the monitoring signal of the tidal flat operation area; The sensor cable is laid along the length of the mudflat operation area and must meet the following conditions: (1) d>D2; (2) (3) Where d is the layout width of the sensor cable, L is the total length of the sensor cable, θ is half of the "∧"-shaped internal angle, D1 and D2 are the length and width of the mudflat operation area, respectively, and R is the spatial resolution of the distributed vibration sensing system.

2. The system for monitoring tidal flats and unusual tides based on distributed optical fiber vibration sensing according to claim 1, characterized in that: The coverage of the sensor cable is larger than the mudflat operation area and is buried underground.

3. The system for monitoring tidal flat freak tides based on distributed optical fiber vibration sensing according to claim 1, characterized in that: The horizontal axis of the spatiotemporal distribution waterfall diagram of the monitoring signal is distance, and the vertical axis is time; the color mapping represents the signal strength, and the brighter the color, the greater the strength.

4. A method for monitoring tidal flat freak tides based on distributed optical fiber vibration sensing, characterized in that: The method is based on the monitoring system according to any one of claims 1 to 3 and is carried out in the following steps: Step 1: Lay the sensor cable in a continuous "∧" shape in the mudflat operation area, and wind one or more cable loops at the top corner of each "∧" shape to anchor the sensor cable; Step 2: Connect the head end of the sensor cable to the distributed vibration sensing system to obtain the backscattered Rayleigh scattering signal along the sensor cable; Step 3: Demodulate the backscattered Rayleigh signal to obtain a spatiotemporal distribution waterfall diagram of the monitoring signal in the mudflat operation area.

5. A method for warning of tidal flat monstrous tides based on distributed optical fiber vibration sensing, characterized in that: The specific steps of the method are: according to the strength of the signal at each sensing distance monitored by the method according to claim 4, when a "strange tide" comes, the highest warning water level that can ensure the safe evacuation of all personnel is calibrated as a level I warning line, that is, when the distributed vibration sensing system detects the level I warning line, all personnel must evacuate immediately; when the tide or waves just touch the sensor cable, it is calibrated as a level II warning line; when the tide or waves have not yet directly touched the sensor cable, it is calibrated as a level III warning line.

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