A debris flow monitoring and early warning method and device

Abstract

The present invention provides a method and device for monitoring and early warning of debris flows, which belongs to the field of geological disaster monitoring. The method divides the debris flow channel after survey and obtains basic geological information, and deploys a "double fishbone" fiber optic monitoring network along both sides of the channel; then collects environmental parameters, presets temperature difference and amplitude difference thresholds; determines whether the debris flow has started at moment i based on the air temperature, temperature sensor temperature, and temperature difference threshold at moment i; if started, extracts the temperature of the temperature sensor at each horizontal position, finds the active sensor to determine the mud water level height value and rising rate value, determines the position of the collapsed object and counts it; then calculates the change in the sound wave amplitude of the acoustic wave sensor from moment i-1 to moment i and compares it with the threshold to determine whether there is foreign matter involved; if so, simultaneously collects the sound wave characteristics of the first acoustic wave sensor on the left and right sides, determines that a debris flow has occurred when they match, and then calculates the flow rate and issues an early warning. The present invention improves the accuracy, stability, and precision of debris flow early warning.

Description

Technical Field

[0001] The present invention belongs to the field of geological disaster monitoring, and in particular relates to a debris flow monitoring and early warning method and device. Background Art

[0002] Debris flow is a natural disaster that usually occurs in mountainous areas. It is characterized by suddenness, fast flow rate, large flow volume, large material capacity and strong destructive power. Real-time monitoring and early warning are usually used to effectively prevent and respond to debris flows.

[0003] The existing technologies for monitoring and early warning of debris flows have the following deficiencies:

[0004] First, there are significant shortcomings in energy consumption. Common equipment used for debris flow monitoring, such as imaging lidar and video surveillance, often requires long-term deployment in outdoor areas such as gullies. These locations often have poor lighting conditions, and even with batteries and solar panels, it's still difficult to generate the power required for normal operation. The equipment's ability to operate continuously is limited, and operations often interrupted due to insufficient power. This not only impacts the continuity of monitoring work, but also significantly increases operational costs and difficulty, creating significant inconvenience for long-term, stable monitoring.

[0005] Second, signal transmission is unstable. Mountainous areas are characterized by complex terrain, with interlaced peaks and valleys, and undulating terrain. This, coupled with unpredictable weather conditions like heavy rain, strong winds, and dense fog, severely interferes with the data transmission links of monitoring equipment. Signal interruptions and packet loss are common during data transmission, preventing crucial monitoring data from being transmitted to the monitoring center on time and accurately. This, in turn, makes it difficult for monitoring personnel to make timely and reliable early warning decisions based on this data, significantly undermining the effectiveness of early warning efforts.

[0006] Third, data transmission capacity is insufficient. In field environments, the data throughput of devices used for equipment communication is generally low, making it difficult to cope with the multi-dimensional, large-scale data collection and transmission requirements generated during the formation of debris flows. For example, during the monitoring process, key data such as sound waves and video streams often emerge in large quantities in a short period of time, but existing equipment is unable to transmit this massive amount of data completely and efficiently to the monitoring center for timely processing. This will undoubtedly cause some valuable data to be lost or delay analysis, which is not conducive to grasping the overall situation of the debris flow.

[0007] Fourth, mud and water level and flow rate data monitoring is inaccurate. This problem is particularly prominent because some monitoring equipment has limited accuracy. In complex and harsh field environments, it is easily affected by various environmental factors such as water impact, sediment accumulation, and electromagnetic interference, resulting in significant deviations from the actual data collected. Furthermore, some equipment frequently malfunctions under extreme environmental conditions, making it impossible to properly capture the true changes in mud and water levels and flow rates. This makes it difficult to accurately determine the likelihood and scale of debris flows, ultimately significantly compromising the timeliness and accuracy of early warnings.

[0008] For example, radar mud level meters used for debris flow monitoring rely on radar waves to measure changes in mud and water levels. Due to their application limitations, the collected data is easily interfered with by the measured water surface quality or wind, and is prone to large abnormal data, with changes ranging from tens of centimeters to tens of meters, which can easily cause trouble for early warning personnel. Another example is video surveillance stations, which have high power consumption, wide video stream bandwidth, and difficulty in transmission except on 4G networks. Summary of the Invention

[0009] In view of the above-mentioned defects or deficiencies in the prior art, the present invention aims to provide a debris flow monitoring and early warning method and device, which can efficiently, stably and accurately monitor and warn of debris flow disasters, and enhance the ability to defend against debris flow disasters.

[0010] In order to achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0011] In a first aspect, an embodiment of the present invention provides a debris flow monitoring and early warning method, the method comprising the following steps:

[0012] Step S1, surveying the area to be monitored, dividing debris flow channels and obtaining basic geological information;

[0013] Step S2: Forming a monitoring plan based on the basic geological information and deploying a "double fishbone" fiber optic monitoring network along both sides of the debris flow channel according to the monitoring plan. The "double fishbone" fiber optic monitoring network includes a backbone transmission fiber and fiber optic temperature sensors, fiber optic acoustic wave sensors, and fiber optic strain sensors connected to the backbone transmission fiber;

[0014] Step S3, collecting environmental parameters of the area to be monitored to form a background database; presetting a temperature difference threshold ΔT0 and a amplitude difference threshold ΔP0;

[0015] Step S4: According to the air temperature T in the background database at time i a (i) and the lowest horizontal temperature T1(i) of the temperature sensor in the "double fishbone" optical fiber monitoring network, calculate ΔT(i) = T1(i)- T a(i); When |ΔT(i)|≥ΔT0, it is determined that the debris flow has started at time i, and step S5 is executed; otherwise, step S11 is executed;

[0016] Step S5: extract the temperature of the temperature sensor at each level, which is T1, ..., T k ,…,T H , when T k (i)-T k When (i-1)≠0, the 1st to kth temperature sensors are active sensors; according to the spacing and number of active sensors, the mud water level height value and the current rising rate value ΔH(i) are determined;

[0017] Step S6: Determine whether there is avalanche at the position q where the strain sensor is arranged according to the strain sensor; if there is avalanche, count the avalanche, and record it as N q ; If it does not exist, then N q =0;

[0018] Step S7, calculating the debris flow velocity and average flow velocity;

[0019] Step S8, performing debris flow warning according to the mud and water level height value, the rising rate value, the location and count of the collapsed objects, the debris flow velocity and the average flow velocity;

[0020] Step S9, monitoring time i=i+1, returning to step S4.

[0021] As a preferred embodiment of the present invention,

[0022] The step S7 comprises:

[0023] Step S71, calculate the change in the acoustic amplitude of the first acoustic wave sensor on either side of the debris flow channel from the i-1th moment to the i-th moment ΔP(i) = P 11 (i)- P 11 (i-1); if ΔP(i)≥ΔP0, it is determined that there is foreign matter in the debris flow channel, and step S72 is executed; if ΔP(i)<ΔP0, it is determined that there is no foreign matter in the debris flow channel, and step S9 is executed;

[0024] Step S72: Simultaneously collect the acoustic wave characteristics F of the first acoustic wave sensor on the left side and the first acoustic wave sensor on the right side of the debris flow channel. 11 and F 21 If F 11 and F 21 If the debris flow matches, it is determined that a debris flow has occurred and step S73 is executed; if F 11 and F 21 If there is no match, it is determined that the debris flow has not occurred and step S9 is executed;

[0025] Step S73: Collect the time difference t between the monitoring signals from the first acoustic wave sensor and the second acoustic wave sensor on either side of the debris flow channel, and calculate the debris flow velocity s = L1 / t as the debris flow velocity monitored by the first acoustic wave sensor, where L1 is the distance between the installation location of the first acoustic wave sensor and the installation location of the second acoustic wave sensor. The debris flow velocity monitored by all acoustic wave sensors is calculated using the same method, and the average debris flow velocity S is calculated.

[0026] and,

[0027] Debris flow channels include source areas, initiation areas, flow areas and affected areas;

[0028] When deploying a "double fishbone" optical fiber monitoring network, the backbone transmission optical fiber on each side of the debris flow channel is set in a fishbone shape;

[0029] On the backbone transmission optical fiber on each side, the optical fiber temperature sensor is deployed in the debris flow initiation area, in physical contact with the mud and water, and is set vertically in the mud and water; the optical fiber acoustic wave sensor is deployed in the debris flow flow area and is set at a predetermined distance from the debris flow channel; the optical fiber strain sensor is deployed in the debris flow source area, placed horizontally and parallel to the slope.

[0030] As a preferred embodiment of the present invention, at least two optical fiber acoustic wave sensors are deployed in the flow area and are arranged at an angle of 45° to the debris flow channel.

[0031] As a preferred embodiment of the present invention, the optical fiber temperature sensor includes an outer tube 111, an inner tube 112, an optical fiber tilt sensor 113, a first optical cable 114 and a second optical cable 115; wherein,

[0032] The outer tube 111 and the inner tube 112 are formed by concentrically fitting two tubes of different diameters. The inner side of the outer tube 111 and the outer side of the inner tube 112 are both provided with thermal insulation coatings. The optical fiber tilt sensor is provided on the upper side of the inner tube. The first optical cable 114 is wound around the lower end of the outer side of the inner tube 112, and the second optical cable 115 is wound around the upper end of the outer side of the inner tube 112.

[0033] The outer cylinder 111 is provided with an outer cylinder window 116; the outer cylinder window 116 is provided on both the front and rear sides of the outer cylinder 111, and each side includes a first section of the lower end of the outer cylinder 111 corresponding to the first optical cable 114 and a second section of the upper end of the outer cylinder 111 corresponding to the second optical cable 115, both of which are configured as rounded strip windows, large enough to expose at least the first optical cable 114 and the second optical cable 115 wound around the inner cylinder 112;

[0034] The first optical cable 114 and the second optical cable 115 are temperature optical cables, each having a plurality of fiber Bragg gratings (FBGs) engraved thereon. The first optical cable 114 is tightly wound around the lower end of the outer side of the inner tube 112 according to first preset parameters, with the winding height extending from the bottom of the tube to a predetermined position. The second optical cable 115 is loosely wound around the upper end of the outer side of the inner tube 112 according to second preset parameters, with the winding height extending from the predetermined position to the top of the tube.

[0035] When the first optical cable 114 is tightly wound, the center-to-center spacing between the cables in the axial direction is adjusted according to the monitoring accuracy requirements; when the second optical cable 115 is loosely wound, the spacing between the cables in the axial direction is greater than the center-to-center spacing of the first optical cable, and the total number of turns is no less than 3 turns; the spacing between the FBGs engraved in the first optical cable 114 and the second optical cable 115 is determined by the outer diameter of the inner tube to ensure that each winding turn contains an FGB.

[0036] As a preferred embodiment of the present invention, in step S5, the mud water level height H is determined and calculated using the following formula:

[0037] H=(k-1)*d (1)

[0038] In formula (1), H represents the height of mud water level rise, k represents the number of active sensors, and d represents the spacing between active sensors.

[0039] As a preferred embodiment of the present invention, in step S6, when determining whether there is a collapsed object at the position q where the strain sensor is arranged based on the strain sensor, the temperature value T6(i) at the current moment i collected by the sixth optical cable is used to calibrate the temperature drift coefficient of the fifth optical cable, and obtain the strain signal after the temperature calibration of the fifth optical cable at the current moment i.

[0040] As a preferred embodiment of the present invention, the sound wave characteristics in step S72 include the amplitude of the main frequency band and the time-frequency power spectrum.

[0041] As a preferred embodiment of the present invention, in step S73, when the debris flow velocity is calculated using the acoustic wave sensor in the flow area, the temperature value T4(i) collected by the fourth optical cable at the current time i is used to calibrate the temperature drift coefficient of the third optical cable, and the acoustic wave signal of the third optical cable after temperature calibration at the current time i is obtained, and the average speed value S(i) of the debris flow migration is calculated by waveform feature matching.

[0042] As a preferred embodiment of the present invention, when performing a debris flow warning in step S8, the warning situation is divided into four levels; the steps include:

[0043] Step S81: determine the change of the difference ΔH(i) between the mud water level value H(i) at the current time i and the mud water level value H(i-1) at the time i-1. If 0<ΔH(i)≤H v , and H(i)≤He , it is judged that the mud water level is rising, but it is a normal water level cycle change and no warning is issued; among them, H v is the mud water level rising rate threshold, H e is the mud water level height threshold;

[0044] Step S82: If 0<ΔH(i)≤H v And H e <H(i), it is judged that the mud water level is rising, exceeding the historical normal water level and rising rate, which is likely to cause flood disasters, and a level 1 warning is issued;

[0045] Step S83, if H v <ΔH(i), and H e <H(i), it is judged that the mud and water level is rising rapidly and is likely to cause mud and rock flow in the short term, and a level 2 warning is issued; if H v <ΔH(i) and H e <H(i) and the number of caving materials in the provenance area is N q ≥Q, where Q is the threshold for the amount of landslide debris. This indicates that the debris flow source is abundant and the conditions for a debris flow outbreak are met, and a Level 3 warning is issued.

[0046] Step S84, if H v <ΔH(i) and H e <H(i) and identify the sound wave enhancement in the debris flow channel, judge that the debris flow is erupting, issue a fourth-level warning, calculate the arrival time of the debris flow based on the average flow velocity S of the debris flow and the total length L of the debris flow channel, send warning information to the public through multimedia, and give time to avoid danger.

[0047] In a second aspect, an embodiment of the present invention further provides a debris flow monitoring and early warning device, the device comprising: a geological information acquisition module, an optical fiber temperature sensor, an optical fiber acoustic wave sensor, an optical fiber strain sensor, a "double fishbone" optical fiber monitoring network construction module, a background data determination module, a temperature start determination module, a mud and water level calculation module, a collapse object determination and counting module, an acoustic foreign body determination module, an acoustic start determination module, a flow velocity calculation module, and an early warning module; wherein,

[0048] The geological information acquisition module is used to survey the area to be monitored, demarcate debris flow channels and obtain basic geological information;

[0049] The optical fiber temperature sensor is used to be deployed in the starting area of the debris flow channel to monitor the temperature;

[0050] The optical fiber acoustic wave sensor is used to be deployed in the flow area of the debris flow channel to monitor the amplitude and frequency of the acoustic wave;

[0051] The optical fiber strain sensor is used to be deployed in the source area of the debris flow channel to locate the collapsed materials;

[0052] The "double fishbone" optical fiber monitoring network construction module is used to form a monitoring plan based on basic geological information, and deploy the "double fishbone" optical fiber monitoring network along both sides of the debris flow channel according to the monitoring plan;

[0053] The background data determination module is used to collect environmental parameters of the area to be monitored to form a background database; it is also used to preset a temperature difference threshold ΔT0 and an amplitude difference threshold ΔP0;

[0054] The temperature start judgment module is used to determine the air temperature T in the background database at the i-th moment. a (i) and the lowest horizontal temperature T1(i) of the temperature sensor in the "double fishbone" optical fiber monitoring network, calculate ΔT(i) = T1(i)- T a (i); When |ΔT(i)|≥ΔT0, it is determined that the debris flow has started at time i and the mud and water level calculation module is started; otherwise, the monitoring at the next time is executed;

[0055] The mud level calculation module is used to extract the temperature of the temperature sensor at each level, which is T1, ..., T k ,…,T H , when T k (i)-T k When (i-1)≠0, the 1st to kth temperature sensors are active sensors; according to the spacing and number of active sensors, the mud water level height value and the current rising rate value ΔH(i) are determined;

[0056] The collapse object determination and counting module is used to determine whether there is collapse object at the position q where the strain sensor is arranged according to the strain sensor; if there is collapse object, the collapse object is counted and recorded as N q ; If it does not exist, then N q =0;

[0057] The acoustic foreign body determination module is used to calculate the change in the acoustic amplitude of the first acoustic sensor on either side of the debris flow channel from the i-1th moment to the i-th moment ΔP(i) = P 11 (i)- P 11 (i-1); if ΔP(i) ≥ ΔP0, it is determined that there is foreign matter in the debris flow channel, and the acoustic wave start-up judgment module is activated; if ΔP(i) < ΔP0, it is determined that there is no foreign matter in the debris flow channel, and the monitoring at the next moment is performed;

[0058] The acoustic wave start determination module is used to simultaneously collect the acoustic wave characteristics F of the first acoustic wave sensor on the left side and the first acoustic wave sensor on the right side of the debris flow channel. 11 and F 21 If F 11 and F21 If the F 11 and F 21 If there is no match, it is determined that the debris flow has not occurred and the monitoring at the next moment is performed;

[0059] The flow velocity calculation module is used to collect the monitoring signal time difference t from the first acoustic wave sensor to the second acoustic wave sensor on either side of the debris flow channel, calculate the flow velocity s=L1 / t of the debris flow as the debris flow velocity monitored by the first acoustic wave sensor, where L1 is the distance between the installation location of the first acoustic wave sensor and the installation location of the second acoustic wave sensor, and use the same method to calculate the debris flow velocity monitored by all acoustic wave sensors, and calculate the average flow velocity S of the debris flow;

[0060] The early warning module is used to issue a debris flow early warning based on the mud and water level height value, the rising rate value, the location and count of collapsed objects, the debris flow velocity and the average flow velocity.

[0061] The technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0062] It can be seen from the above technical solutions that the debris flow monitoring and early warning method or device provided by the embodiment of the present invention can monitor and warn debris flows by setting up a distributed "double fishbone" optical fiber monitoring network, which can effectively monitor the dynamic changes of debris flows from initiation to outbreak in real time, and provide early warning levels and early warning times. On the one hand, an optical fiber temperature sensor is used to collect the temperature changes of the water level in the debris flow channel, and then the two parameters of the water level rise and the rate of increase are calculated to determine whether the debris flow has started; because the temperature sensor is in direct contact with the flowing water, it can obtain accurate data without being interfered by the environment or electromagnetic interference. On the other hand, an optical fiber strain sensor is used to monitor the collapse of materials in the source area, and the collapse of materials is counted according to the strain signal of the strain sensor, so as to locate the position and scale of the collapse of materials, and then determine the degree of danger of the erupting debris flow. Third, fiber optic acoustic sensors are deployed at corresponding locations on both sides of the debris flow channel. By matching the data collected by these sensors, it is possible to determine whether a debris flow has occurred. If so, the average speed of the debris flow and its arrival time at the affected area are calculated, providing early warning to the affected area and providing sufficient time for response. Fourth, the use of non-electrical optical fibers as sensors and transmission networks for debris flow monitoring and early warning can overcome the problems of existing monitoring equipment, such as high power consumption, unstable transmission, low data throughput, and poor monitoring accuracy.

[0063] Of course, it is not necessary to achieve all of the advantages described above simultaneously in order to implement any product or method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0065] Figure 1 is a flow chart of the debris flow monitoring and early warning method according to an embodiment of the present invention;

[0066] Figure 2 Schematic diagram of sensor distribution in a debris flow monitoring and early warning system according to an embodiment of the present invention;

[0067] Figure 3 yes Figure 2 Schematic diagram of the optical fiber temperature sensor structure;

[0068] Figure 4 yes Figure 2 Schematic diagram of the fiber optic acoustic wave sensor structure;

[0069] Figure 5 yes Figure 2 Schematic diagram of the optical fiber strain sensor structure.

[0070] Description of reference numerals:

[0071] 1-"Double fishbone" fiber optic monitoring network; 11-Fiber optic temperature sensor; 111-Outer tube; 112-Inner tube; 113-Fiber optic tilt sensor; 114-First optical cable; 115-Second optical cable; 116-Window in outer tube; 12-Fiber optic acoustic wave sensor; 121-Acoustic wave cylinder; 122-Acoustic wave sealing adhesive; 123-Third optical cable; 124-Fourth optical cable; 13-Fiber optic strain sensor; 131-Strain cylinder; 132-Strain sealing adhesive; 133-Fifth optical cable; 134-Sixth optical cable; 14-Backbone transmission optical fiber; 2-Debris flow channel; 3-Debris flow acoustic wave. DETAILED DESCRIPTION

[0072] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. It should be noted that the embodiments of the present invention and the features in the embodiments can also be combined with each other in the absence of conflict.

[0073] It should be noted that similar reference numerals and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures. In the description of the present invention, the terms "first," "second," "third," "fourth," etc. are used only to distinguish the description and are not to be understood as indicating or implying relative importance.

[0074] Based on the demand for monitoring and early warning of debris flow disasters, an embodiment of the present invention provides a debris flow monitoring and early warning method and device, which is based on the distributed setting of optical fiber sensors to achieve distributed measurement of disaster warning-related parameters along the entire length of the optical fiber, and then process and analyze the data collected by the optical fiber sensors to improve the stability, accuracy and precision of debris flow early warning and improve the early warning efficiency.

[0075] like Figure 1 As shown, the debris flow monitoring and early warning method provided by the embodiment of the present invention includes the following steps:

[0076] Step S1: survey the area to be monitored, divide the debris flow channel and obtain basic geological information.

[0077] In this step, the area to be monitored is generally the target debris flow channel, which includes a source area, a starting area, a circulation area, and a disaster-stricken area. The basic geological information obtained includes the distribution, scope of action, and line length (length along the direction of the debris flow channel) of the debris flow source area, starting area, circulation area, and disaster-stricken area in the area to be monitored. Among them, the source area is the area where accumulation is formed, including landslides, collapses, and materials falling downward from unstable slopes. Generally, if there is a source area, debris flow can be formed under the action of rainwater, and if there is no source area, floods will be formed; the starting area is the downstream of the source area, where the debris flow has just formed and is the location where the debris flow starts; the circulation area is the middle reaches of the debris flow channel, where a large-scale debris flow disaster has already formed; the disaster-stricken area is the downstream of the debris flow channel, where there are residents, and when the debris flow passes through, it will cause human and economic losses and disasters.

[0078] Step S2, forming a monitoring plan based on the basic geological information, and deploying a "double fishbone" fiber optic monitoring network 1 along both sides of the debris flow channel according to the monitoring plan. The "double fishbone" fiber optic monitoring network 1 includes a backbone transmission optical fiber 14 and an optical fiber temperature sensor 11, an optical fiber acoustic wave sensor 12 and an optical fiber strain sensor 13 connected to the backbone transmission optical fiber.

[0079] In this step, the monitoring scheme includes monitoring parameters, the number and location of monitoring points. The selection of the monitoring parameters is determined according to the actual debris flow type. For example, for rainfall-type debris flows with rich material sources, the monitoring parameters include mud-water level rise parameters, debris flow velocity parameters, and material migration parameters in the material source area. The material migration parameters in the material source area refer to changes in the material source area, including the presence or absence of landslides, and whether the scale, location, and composition of the deposits have changed. For rainfall-type debris flows with less material sources, the monitoring parameters include mud-water level rise parameters, debris flow velocity parameters, etc., and the monitoring of material migration parameters is appropriately reduced. The number and location of the monitoring points are determined according to the characteristics of the debris flow channel. On the one hand, the number of monitoring points needs to be selected according to the length of the debris flow channel. On the other hand, monitoring points should be set separately in the channel sections with different material compositions and the channels where the water-heat drop exceeds the threshold.

[0080] like Figure 2 As shown, when deploying a "double fishbone" fiber optic monitoring network 1, the backbone transmission fibers on each side of the debris flow channel are arranged in a fishbone pattern. Fiber optic temperature sensors 11 are deployed in the debris flow initiation zone, in physical contact with the muddy water. These fiber optic temperature sensors are based on Bragg grating (FBG) fibers, exploiting their temperature sensitivity. Preferably, the fiber optic temperature sensors are positioned vertically within the muddy water. Fiber optic acoustic wave sensors 12 are deployed in the debris flow flow zone, at a predetermined distance from the debris flow channel. At least two fiber optic acoustic wave sensors 12 are arranged in the flow zone, at a 45° angle to the debris flow channel, to enhance the axial receiving sensitivity of the acoustic wave sensors 12. The optical fiber strain sensor 13 is deployed in the debris flow source area. It is designed based on fiber Bragg grating (FBG) and utilizes the sensitivity of strain grating optical fiber to strain. It is placed horizontally and parallel to the slope. When a landslide falls, the optical fiber strain sensor can sense the strain of the monitoring equipment and determine the scale of the landslide. In combination with at least three other optical fiber acoustic wave sensors, it can locate the type of abnormal vibration, improve the monitoring anti-interference ability, and accurately monitor the location of the landslide.

[0081] In addition, in a preferred embodiment, fiber optic acoustic sensors can also be installed in the provenance area. At least three fiber optic acoustic sensors 12 are arranged in the provenance area, with the center points of the three optical fiber acoustic sensors 12 forming a triangle. Two of the sensors are positioned horizontally at a 45° angle to the debris flow channel, and the third is positioned horizontally and parallel to the debris flow channel. For the acoustic sensors in the provenance area, a time difference of arrival (TDOA) positioning method is used, combined with a "double fishbone" monitoring network, to form a triangular network for landslide monitoring, achieving triangulated location of the landslide. When triangulating using the three acoustic sensors, if the landslide is within the triangulated network, the location of the landslide can be directly calculated. However, the acoustic sensor signal at this time could be generated by the landslide, a passing pedestrian, or an animal, and cannot be uniquely confirmed as the landslide that caused the debris flow. If the landslide is outside the triangulated network, the direction of the landslide is first determined using a strain sensor, and then a unique location is calculated using triangulation. Landslides that can be simultaneously determined by the strain sensor and the acoustic sensor can be uniquely confirmed as the landslide.

[0082] like Figure 3As shown, the structure of the fiber optic temperature sensor includes an outer tube 111, an inner tube 112, a fiber optic tilt sensor 113, a first optical cable 114, and a second optical cable 115. The outer tube 111 is provided with an outer tube window 116. The outer tube 111 and the inner tube 112 are formed by concentrically fitting two tubes of different diameters. Preferably, the outer tube 111 and the inner tube 112 are made of stainless steel, with a height of 1.5-2.5 meters, typically 2 meters. The gap between the outer tube 111 and the inner tube 112 is set to 8-15 cm, typically 10 cm. The outer tube 111 and the inner tube 112 are each provided with a thermal insulation coating, which can be made of aerogel material. A first optical cable 114 is wound around the lower end of the outer tube 112, and a second optical cable 115 is wound around the upper end of the outer tube 112. Windows 116 are located on both the front and rear sides of the outer tube 111. Each side includes a first section of the first optical cable at the lower end of the outer tube 111, corresponding to the first section of the first optical cable, and a second section of the second optical cable at the upper end of the outer tube 111. These windows are rounded strips large enough to expose at least the first and second optical cables wound around the inner tube. For example, if the tube is 2 meters high, the window size is generally at least 1500 cm from the lowest point to the highest point. The first optical cable is a temperature-controlled cable and is tightly wound around the lower end of the inner tube 112 according to first preset parameters, with a winding height from the bottom of the tube to a predetermined position (generally 1500 mm for a 2-meter tube height). The second optical cable is a temperature-controlled cable and is loosely wound around the upper end of the inner tube 112 according to second preset parameters, with a winding height from the predetermined position to the top of the tube. Both the first and second optical cables are engraved with multiple fiber Bragg gratings (FBGs). When the first optical cable is tightly wound, the axial spacing between the cables is adjusted based on the required monitoring accuracy. For example, if a monitoring accuracy of 5mm is required, a cable with a wrapping less than 5mm can be used, with the center-to-center spacing of 5mm between two turns. If a monitoring accuracy of 20mm is required, a cable with a wrapping less than 10mm can be used, with the center-to-center spacing of 20mm between two turns. When the second optical cable is loosely wound, the axial spacing between the cables can be increased, with no specific requirements, but the minimum spacing must be three turns. The spacing between the FBGs engraved in the first and second optical cables is determined by the outer diameter of the inner barrel, ensuring that each winding contains an FBG.

[0083] like Figure 4As shown, the fiber optic acoustic wave sensor 12 is designed based on Bragg grating (FBG) optical fiber, utilizing the sensitivity of acoustic wave grating optical fiber to vibration. It comprises an acoustic wave cylinder 121, an acoustic wave sealing adhesive 122, a third optical cable 123, and a fourth optical cable 124. The acoustic wave cylinder 121 is a single-layer stainless steel cylinder, preferably with a diameter of 60 mm and a length of 600 mm. The third optical cable 123 is an acoustic wave cable, engraved with the FBG, bonded to the inside of the cylinder. The fourth optical cable 124 is a temperature cable, engraved with the FBG, bonded to the inside of the cylinder. The acoustic wave sealing adhesive is an anaerobic adhesive, used to bond the third and fourth optical cables 123, 124 to the stainless steel cylinder and fill the interior of the acoustic wave cylinder 121. For the acoustic wave sensors in the circulation area, starting from the boundary between the circulation area and the source area, the first acoustic wave sensor and the second acoustic wave sensor on the left and the first acoustic wave sensor and the second acoustic wave sensor on the right are respectively set on both sides of the channel. If the channel circulation area is long, the third acoustic wave sensor, the fourth acoustic wave sensor, etc. can also be set on both sides.

[0084] like Figure 5 As shown, the optical fiber strain sensor 13 includes a strain cylinder 131, a fifth optical cable 133, a sixth optical cable 134, and a strain sealant 132. The strain cylinder 131 is a single-layer stainless steel cylinder, preferably with a diameter of 60 mm and a length of 2000 mm. The fifth optical cable 133 is a strain cable, engraved with a fiber optic guide glass (FBG), bonded to the inside of the cylinder. The sixth optical cable is a temperature cable, engraved with a fiber optic guide glass (FBG) bonded to the inside of the cylinder. The strain sealant 132 is an anaerobic adhesive used to bond the fifth and sixth optical cables 133, 134 to the stainless steel cylinder and fill the interior of the strain cylinder 131.

[0085] Step S3, collecting environmental parameters of the area to be monitored to form a background database; presetting a temperature difference threshold ΔT0 and a amplitude difference threshold ΔP0.

[0086] In this step, the environmental parameters include the temperature at each monitoring point, air temperature, surface acoustic wave propagation velocity in different material composition sections, and the background acoustic wave characteristics of the debris flow channel. The two monitoring thresholds are determined based on actual conditions, field experiments, or experience.

[0087] Step S4: According to the air temperature T in the background database at time i a (i) and the lowest horizontal temperature T1(i) of the temperature sensor in the "double fishbone" optical fiber monitoring network, calculate ΔT(i) = T1(i)- T a (i); When |ΔT(i)|≥ΔT0, it is determined that the debris flow has started at time i, and step S5 is executed; otherwise, step S11 is executed.

[0088] Step S5: extract the temperature of the temperature sensor at each level, which is T1, ..., T k ,…,T H , when T k (i)-T k When (i-1)≠0, the 1st to kth temperature sensors are active sensors; according to the spacing and number of active sensors, the mud water level height value and the current rising rate value ΔH(i) are determined.

[0089] In this step, the mud water level height H is determined using the following formula:

[0090] H=(k-1)*d (1)

[0091] In formula (1), H represents the height of mud water level rise, k represents the number of active sensors, and d represents the spacing between active sensors.

[0092] Specifically, when using Figure 3 The fiber optic temperature sensor shown here monitors mud and water levels. A first optical cable is tightly wound around the outside of an inner tube. Each coil of the cable features a temperature-sensing grating (BGR). A fiber optic interrogator uses a laser to transmit light waves to the BGR, receives the light signals reflected from each BGR, and calculates the temperature change. If the light signal returned by a particular BGR changes, demodulation reveals that the temperature of that BGR is the same as the temperature of the BGR below it and different from the BGR of the second optical cable. This indicates that the mud and water level has risen to that BGR. If the temperatures of multiple BGRs change, the water level has risen significantly. The second optical cable serves as a reference and monitors the air temperature. Aerogel coatings on the outer and inner sides of the double-cylinder tube reduce thermal conductivity interference within the steel cylinder. Window openings in the outer tube allow water to enter the outer tube and fully contact the fiber grating (FBG) in the inner tube. Furthermore, the outer tube protects the fiber grating (FBG) in the inner tube from damage caused by mud and rocks. A fiber optic inclinometer or tilt sensor is located at the top of the tube to determine the verticality of the tube in real time, ensuring accurate water level monitoring. If the cylinder is knocked over by mud and water, abnormal data can also be eliminated.

[0093] Step S6: Determine whether there is avalanche at the position q where the strain sensor is arranged according to the strain sensor; if there is avalanche, count the avalanche, and record it as N q ; If it does not exist, then N q =0.

[0094] In this step, when the strain sensor is used to determine whether there is a collapsed object at the position q where the strain sensor is arranged, the temperature value T6(i) collected by the sixth optical cable at the current time i is used to calibrate the temperature drift coefficient of the fifth optical cable, and obtain the strain signal of the fifth optical cable after temperature calibration at the current time i.

[0095] This step can also be further confirmed and determined using three fiber optic acoustic sensors placed in the provenance area, as well as the number of avalanches. At this point, the acoustic signals collected by the three acoustic sensors at three locations are used to calculate the specific location of the avalanche using the principle of triangulation and provide a status value, Y or N. The three acoustic sensors at these three locations are selected based on the monitoring network. Y indicates the presence of avalanches, and N indicates the absence of avalanches.

[0096] Step S7, calculating the debris flow velocity and average flow velocity.

[0097] Specifically, this step includes:

[0098] Step S71, calculate the change in the acoustic amplitude of the first acoustic wave sensor on either side of the debris flow channel from the i-1th moment to the i-th moment ΔP(i) = P 11 (i)- P 11 (i-1); if ΔP(i)≥ΔP0, it is determined that there is foreign matter involved in the debris flow channel, and step S72 is executed; if ΔP(i)<ΔP0, it is determined that there is no foreign matter involved in the debris flow channel, and step S9 is executed.

[0099] Step S72: Simultaneously collect the acoustic wave characteristics F of the first acoustic wave sensor on the left side and the first acoustic wave sensor on the right side of the debris flow channel. 11 and F 21 If F 11 and F 21 If the debris flow matches, it is determined that a debris flow has occurred and step S73 is executed; if F 11 and F 21 If there is no match, it is determined that the debris flow has not occurred and step S9 is executed.

[0100] In this step, the sound wave characteristics include the amplitude of the main frequency band and the time-frequency power spectrum.

[0101] Step S73, collect the monitoring signal time difference t from the first acoustic wave sensor to the second acoustic wave sensor on either side of the debris flow channel, calculate the debris flow velocity s=L1 / t as the debris flow velocity monitored by the first acoustic wave sensor, L1 is the distance between the installation position of the first acoustic wave sensor and the installation position of the second acoustic wave sensor, use the same method to calculate the debris flow velocity monitored by all acoustic wave sensors, and calculate the average debris flow velocity S.

[0102] In this step, when using the acoustic wave sensor in the flow zone to calculate the debris flow velocity, the temperature value T4(i) collected by the fourth optical cable at time i is used to calibrate the temperature drift coefficient of the third optical cable. The temperature-calibrated acoustic wave signal of the third optical cable at time i is obtained, and the debris flow velocity S(i) is calculated by waveform feature matching. When calculating the average debris flow velocity S, either integration or averaging can be used.

[0103] Step S8, issuing a debris flow warning based on the mud and water level height value, the rising rate value, the location and count of landslides, the debris flow velocity and the average flow velocity.

[0104] In this step, preferably, the warning situation is divided into four levels. The specific warning includes the following steps:

[0105] Step S81: determine the change of the difference ΔH(i) between the mud water level value H(i) at the current time i and the mud water level value H(i-1) at the time i-1. If 0<ΔH(i)≤H v , and H(i)≤H e , it is judged that the mud water level is rising, but it is a normal water level cycle change and no warning is issued; among them, H v is the mud water level rising rate threshold, H e is the mud water level height threshold;

[0106] Step S82: If 0<ΔH(i)≤H v And H e <H(i), it is judged that the mud water level is rising, exceeding the historical normal water level and rising rate, which is likely to cause flood disasters, and a level 1 warning is issued;

[0107] Step S83, if H v <ΔH(i), and H e <H(i), it is judged that the mud and water level is rising rapidly and is likely to cause mud and rock flow in the short term, and a level 2 warning is issued; if H v <ΔH(i) and H e <H(i) and the number of caving materials in the provenance area is N q ≥Q, where Q is the threshold for the amount of landslide debris. This indicates that the debris flow source is abundant and the conditions for a debris flow outbreak are met, and a Level 3 warning is issued.

[0108] Step S84, if H v <ΔH(i) and H e <H(i) and identify the sound wave enhancement in the debris flow channel, judge that the debris flow is erupting, issue a level 4 warning, calculate the arrival time of the debris flow based on the average flow velocity S of the debris flow and the total length L of the debris flow channel, send warning information to the public through multimedia such as warning broadcasts and text messages, and provide time to take shelter.

[0109] Step S9, monitoring time i=i+1, returning to step S4.

[0110] Based on the same concept, an embodiment of the present invention further provides a debris flow monitoring and early warning device, comprising: a geological information acquisition module, an optical fiber temperature sensor, an optical fiber acoustic sensor, an optical fiber strain sensor, a "double fishbone" optical fiber monitoring network construction module, a background data determination module, a temperature start determination module, a mud and water level calculation module, a landslide determination and counting module, an acoustic foreign body determination module, an acoustic start determination module, a flow velocity calculation module, and an early warning module;

[0111] The geological information acquisition module is used to survey the area to be monitored, demarcate debris flow channels and obtain basic geological information;

[0112] The optical fiber temperature sensor is used to be deployed in the starting area of the debris flow channel to monitor the temperature;

[0113] The optical fiber acoustic wave sensor is used to be deployed in the flow area of the debris flow channel to monitor the amplitude and frequency of the acoustic wave;

[0114] The optical fiber strain sensor is used to be deployed in the source area of the debris flow channel to locate the collapsed materials;

[0115] The "double fishbone" optical fiber monitoring network construction module is used to form a monitoring plan based on basic geological information, and deploy the "double fishbone" optical fiber monitoring network along both sides of the debris flow channel according to the monitoring plan;

[0116] The background data determination module is used to collect environmental parameters of the area to be monitored to form a background database; it is also used to preset a temperature difference threshold ΔT0 and an amplitude difference threshold ΔP0;

[0117] The temperature start judgment module is used to determine the air temperature T in the background database at the i-th moment. a (i) and the lowest horizontal temperature T1(i) of the temperature sensor in the "double fishbone" optical fiber monitoring network, calculate ΔT(i) = T1(i)- T a (i); When |ΔT(i)|≥ΔT0, it is determined that the debris flow has started at time i and the mud and water level calculation module is started; otherwise, the monitoring at the next time is executed;

[0118] The mud level calculation module is used to extract the temperature of the temperature sensor at each level, which is T1, ..., T k ,…,T H , when T k (i)-T k When (i-1)≠0, the 1st to kth temperature sensors are active sensors; according to the spacing and number of active sensors, the mud water level height value and the current rising rate value ΔH(i) are determined;

[0119] The collapse object determination and counting module is used to determine whether there is collapse object at the position q where the strain sensor is arranged according to the strain sensor; if there is collapse object, the collapse object is counted and recorded as N q ; If it does not exist, then N q =0;

[0120] The acoustic foreign body determination module is used to calculate the change in the acoustic amplitude of the first acoustic sensor on either side of the debris flow channel from the i-1th moment to the i-th moment ΔP(i) = P 11 (i)- P 11 (i-1); if ΔP(i) ≥ ΔP0, it is determined that there is foreign matter in the debris flow channel, and the acoustic wave start-up judgment module is activated; if ΔP(i) < ΔP0, it is determined that there is no foreign matter in the debris flow channel, and the monitoring at the next moment is performed;

[0121] The acoustic wave start determination module is used to simultaneously collect the acoustic wave characteristics F of the first acoustic wave sensor on the left side and the first acoustic wave sensor on the right side of the debris flow channel. 11 and F 21 If F 11 and F 21 If the F 11 and F 21 If there is no match, it is determined that the debris flow has not occurred and the monitoring at the next moment is performed;

[0122] The flow velocity calculation module is used to collect the time difference t of the monitoring signal from the first acoustic wave sensor to the second acoustic wave sensor on either side of the debris flow channel, calculate the flow velocity s=L1 / t of the debris flow, and use it as the flow velocity of the debris flow monitored by the first acoustic wave sensor, where L1 is the distance between the installation location of the first acoustic wave sensor and the installation location of the second acoustic wave sensor. The same method is used to calculate the flow velocity of the debris flow monitored by all acoustic wave sensors, and the average flow velocity S of the debris flow is calculated;

[0123] The early warning module is used to issue a debris flow early warning based on the mud and water level height value, the rising rate value, the location and count of collapsed objects, the debris flow velocity and the average flow velocity.

[0124] In this embodiment, each module is implemented by a processor, and a memory is appropriately added when storage is required. The processor may be, but is not limited to, a microprocessor MPU, a central processing unit (CPU), a network processor (NP), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), other programmable logic devices, discrete gates, transistor logic devices, discrete hardware components, etc. The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage. Optionally, the memory may also be at least one storage device located away from the aforementioned processor.

[0125] In the above embodiments, all or part of the embodiments may be implemented using software, hardware, firmware, or any combination thereof. When implemented using software, all or part of the embodiments may be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the processes or functions described in accordance with the embodiments of the present invention are generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means.

[0126] It should also be noted that the debris flow monitoring and early warning device described in this embodiment corresponds to the debris flow monitoring and early warning method described, and the description and limitation of the method are also applicable to the system and will not be repeated here.

[0127] As can be seen from the above technical solutions, the debris flow monitoring and early warning method or device provided by the embodiments of the present invention utilizes a distributed "double fishbone" optical fiber monitoring network to monitor and early warning debris flows. This effectively monitors the dynamic changes of debris flows in real time, from initiation to outbreak, and provides warning levels and timeframes. First, optical fiber temperature sensors are used to collect temperature changes in the water level in the debris flow channel, and then calculate the water level rise and rate of rise to determine whether a debris flow has initiated. Because the temperature sensors are in direct contact with the flowing water, they can obtain accurate data without environmental or electromagnetic interference. Second, optical fiber strain sensors are used to monitor and count the amount of debris falling in the source area, determining its location and size, and thus assessing the risk of a debris flow outbreak. Third, optical fiber acoustic wave sensors are deployed at corresponding locations on either side of the debris flow channel. By matching the data collected by these acoustic wave sensors, it is possible to determine whether a debris flow has occurred. If so, the average velocity of the debris flow and its arrival time are calculated, providing early warning to the affected area and providing sufficient time for response. Fourthly, the use of non-electrical optical fibers as sensors and transmission networks for debris flow monitoring and early warning can overcome the problems of high power consumption, unstable transmission, low data throughput, and poor monitoring accuracy of existing monitoring equipment.

[0128] The above description is only a preferred embodiment of the present invention and an explanation of the technical principles used. It is not intended to limit the scope of the invention to be protected, but merely represents a preferred embodiment of the present invention. Those skilled in the art should understand that the scope of the invention involved in the present invention is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. A debris flow monitoring and early warning method, characterized in that: The method comprises the following steps: Step S1, surveying the area to be monitored, dividing the debris flow channel and obtaining basic geological information; the debris flow channel includes the source area, the starting area, the flow area and the affected area; Step S2: Forming a monitoring plan based on basic geological information, and deploying a "double fishbone" fiber optic monitoring network along both sides of the debris flow channel according to the monitoring plan. The fiber optic monitoring network includes a backbone transmission fiber and fiber optic temperature sensors, fiber optic acoustic sensors, and fiber optic strain sensors connected to the backbone transmission fiber. When deploying the "double fishbone" fiber optic monitoring network, the backbone transmission fiber on each side of the debris flow channel is arranged in a fishbone shape. On each side of the backbone transmission fiber, the fiber optic temperature sensor is deployed in the debris flow initiation area, in physical contact with the muddy water, and is vertically arranged in the muddy water. The fiber optic acoustic sensor is deployed in the debris flow flow area and is set at a predetermined distance from the debris flow channel. The fiber optic strain sensor is deployed in the debris flow source area, placed horizontally and parallel to the slope. Step S3, collecting environmental parameters of the area to be monitored to form a background database; Preset temperature difference threshold ΔT0, preset amplitude difference threshold ΔP0; Step S4: According to the air temperature T in the background database at time i a (i) and the lowest level temperature T1(i) of the temperature sensor in the optical fiber monitoring network, calculate ΔT(i) = T1(i)- T a (i); When |ΔT(i)|≥ΔT0, it is determined that the debris flow has started at time i, and step S5 is executed; Otherwise, execute step S9; Step S5: extract the temperature of the temperature sensor at each level, which is T1, ..., T k ,…,T H , when T k (i)-T k When (i-1)≠0, the 1st to kth temperature sensors are active sensors; according to the spacing and number of active sensors, the mud water level height value and the current rising rate value ΔH(i) are determined; Step S6: Determine whether there is avalanche at the position q where the strain sensor is arranged according to the strain sensor; if there is avalanche, count the avalanche, and record it as N q ; If it does not exist, then N q =0; Step S7, calculating the debris flow velocity and average flow velocity; Step S8, issuing a debris flow warning based on the mud and water level height value, the rising rate value, the location and count of the collapsed objects, the debris flow velocity and the average flow velocity; and the warning situation is divided into four levels; including the following steps: Step S81: determine the change of the difference ΔH(i) between the mud water level value H(i) at the current time i and the mud water level value H(i-1) at the time i-1. If 0<ΔH(i)≤H v , and H(i)≤H e , it is judged that the mud water level is rising, but it is a normal water level cycle change and no warning is issued; among them, H v is the mud water level rising rate threshold, H e is the mud water level height threshold; Step S82: If 0<ΔH(i)≤H v And H e <H(i), it is judged that the mud water level is rising, exceeding the historical normal water level and rising rate, which is likely to cause flood disasters, and a level 1 warning is issued; Step S83, if H v <ΔH(i), and H e <H(i), it is judged that the mud and water level is rising rapidly and is likely to cause mud and rock flow in the short term, and a level 2 warning is issued; if H v <ΔH(i) and H e <H(i) and the number of caving materials in the provenance area is N q ≥Q, where Q is the threshold for the amount of landslide debris. This indicates that the debris flow source is abundant and the conditions for a debris flow outbreak are met, and a Level 3 warning is issued. Step S84, if H v <ΔH(i) and H e <H(i) and the presence of acoustic wave enhancement in the debris flow channel is detected, and a debris flow outbreak is determined. A level 4 warning is issued, and the arrival time of the debris flow is calculated based on the average flow velocity S and the total length L of the debris flow channel. Warning information is issued to the public through multimedia, and a time to avoid danger is given; Step S9, monitoring time i=i+1, returning to step S4; and, The optical fiber temperature sensor includes an outer tube, an inner tube, an optical fiber tilt sensor, a first optical cable and a second optical cable; wherein, The outer and inner tubes are formed by concentrically fitting two tubes of different diameters. Heat-insulating coatings are applied to the inner and outer sides of the outer and inner tubes, respectively. A fiber optic tilt sensor is mounted on the upper side of the inner tube. A first optical cable is wound around the lower end of the outer side of the inner tube, while a second optical cable is wound around the upper end of the outer side of the inner tube. The outer tube is provided with an outer tube window; the outer tube window is provided on the front and rear sides of the outer tube, each side including a first section of the first optical cable corresponding to the lower end of the outer tube and a second section of the second optical cable corresponding to the upper end of the outer tube, both of which are configured as rounded strip windows, and are large enough to expose at least the first optical cable and the second optical cable wound on the inner tube; The first optical cable and the second optical cable are temperature optical cables, each having a plurality of fiber Bragg gratings (FBGs) engraved thereon. The first optical cable is tightly wound around the lower end of the outer side of the inner tube according to first preset parameters, with the winding height extending from the bottom of the tube to a predetermined position. The second optical cable is loosely wound around the upper end of the outer side of the inner tube according to second preset parameters, with the winding height extending from the predetermined position to the top of the tube. When the first optical cable is tightly wound, the center-to-center spacing between the cables in the axial direction is adjusted according to the monitoring accuracy requirements; when the second optical cable is loosely wound, the spacing between the cables in the axial direction is greater than the center-to-center spacing of the first optical cable, and the total number of turns is no less than 3 turns; the spacing between the FBGs engraved in the first and second optical cables is determined by the outer diameter of the inner tube to ensure that each winding turn contains an FGB.

2. The debris flow monitoring and early warning method according to claim 1, characterized in that: The step S7 comprises: Step S71, calculate the change in the acoustic amplitude of the first acoustic wave sensor on either side of the debris flow channel from the i-1th moment to the i-th moment ΔP(i) = P 11 (i)- P 11 (i-1); if ΔP(i)≥ΔP0, it is determined that there is foreign matter in the debris flow channel, and step S72 is executed; if ΔP(i)<ΔP0, it is determined that there is no foreign matter in the debris flow channel, and step S9 is executed; Step S72: Simultaneously collect the acoustic wave characteristics F of the first acoustic wave sensor on the left side and the first acoustic wave sensor on the right side of the debris flow channel. 11 and F 21 If F 11 and F 21 If the debris flow matches, it is determined that a debris flow has occurred and step S73 is executed; if F 11 and F 21 If there is no match, it is determined that the debris flow has not occurred and step S9 is executed; Step S73, collect the monitoring signal time difference t from the first acoustic wave sensor to the second acoustic wave sensor on either side of the debris flow channel, calculate the debris flow velocity s=L1 / t as the debris flow velocity monitored by the first acoustic wave sensor, L1 is the distance between the installation position of the first acoustic wave sensor and the installation position of the second acoustic wave sensor, use the same method to calculate the debris flow velocity monitored by all acoustic wave sensors, and calculate the average debris flow velocity S.

3. The debris flow monitoring and early warning method according to claim 2, characterized in that: At least two fiber optic acoustic wave sensors are deployed in the flow area and are arranged at a 45° angle to the debris flow channel.

4. The debris flow monitoring and early warning method according to claim 1, characterized in that: In step S5, the mud water level height H is determined and calculated using the following formula: H=(k-1)*d (1) In formula (1), H represents the height of mud water level rise, k represents the number of active sensors, and d represents the spacing between active sensors.

5. The debris flow monitoring and early warning method according to claim 1, characterized in that: In step S6, when the strain sensor is used to determine whether there is a collapsed object at the position q where the strain sensor is arranged, the temperature value T6(i) collected by the sixth optical cable at the current time i is used to calibrate the temperature drift coefficient of the fifth optical cable to obtain the strain signal after the temperature calibration of the fifth optical cable at the current time i.

6. The debris flow monitoring and early warning method according to claim 2, characterized in that: The sound wave characteristics in step S72 include the amplitude of the main frequency band and the time-frequency power spectrum.

7. The debris flow monitoring and early warning method according to claim 2, characterized in that: In step S73, when the acoustic wave sensor in the flow area is used to calculate the debris flow velocity, the temperature value T4(i) collected by the fourth optical cable at the current time i is used to calibrate the temperature drift coefficient of the third optical cable, and the acoustic wave signal of the third optical cable after temperature calibration at the current time i is obtained. The average speed value S(i) of the debris flow migration is calculated by waveform feature matching.

8. A debris flow monitoring and early warning device, characterized in that: The device includes: a geological information acquisition module, an optical fiber temperature sensor, an optical fiber acoustic wave sensor, an optical fiber strain sensor, a "double fishbone" optical fiber monitoring network construction module, a background data determination module, a temperature start judgment module, a mud and water level calculation module, a collapse object judgment and counting module, an acoustic foreign body judgment module, an acoustic start judgment module, a flow rate calculation module and an early warning module; wherein, The geological information acquisition module is used to survey the monitored area, divide the debris flow channel and obtain basic geological information; the debris flow channel includes the source area, the starting area, the flow area and the disaster area; The optical fiber temperature sensor is used to be arranged in the starting area of the debris flow channel, in physical contact with the muddy water, and vertically arranged in the muddy water to monitor the temperature; and, The optical fiber temperature sensor includes an outer tube, an inner tube, an optical fiber tilt sensor, a first optical cable and a second optical cable; wherein, The outer and inner tubes are formed by concentrically fitting two tubes of different diameters. Heat-insulating coatings are applied to the inner and outer sides of the outer and inner tubes, respectively. A fiber optic tilt sensor is mounted on the upper side of the inner tube. A first optical cable is wound around the lower end of the outer side of the inner tube, while a second optical cable is wound around the upper end of the outer side of the inner tube. The outer tube is provided with an outer tube window; the outer tube window is provided on the front and rear sides of the outer tube, each side including a first section of the first optical cable corresponding to the lower end of the outer tube and a second section of the second optical cable corresponding to the upper end of the outer tube, both of which are configured as rounded strip windows, and are large enough to expose at least the first optical cable and the second optical cable wound on the inner tube; The first optical cable and the second optical cable are temperature optical cables, each having a plurality of fiber Bragg gratings (FBGs) engraved thereon. The first optical cable is tightly wound around the lower end of the outer side of the inner tube according to first preset parameters, with the winding height extending from the bottom of the tube to a predetermined position. The second optical cable is loosely wound around the upper end of the outer side of the inner tube according to second preset parameters, with the winding height extending from the predetermined position to the top of the tube. When the first optical cable is tightly wound, the center spacing between the cables in the axial direction is adjusted according to the monitoring accuracy requirements; when the second optical cable is loosely wound, the spacing between the cables in the axial direction is greater than the center spacing between the cables of the first optical cable, and the total number of turns is not less than 3 turns; the spacing between the FBGs engraved in the first and second optical cables is determined by the outer diameter of the inner tube to ensure that each winding turn contains an FGB; The optical fiber acoustic wave sensor is used to be arranged in the flow area of the debris flow channel and set at a predetermined distance from the debris flow channel to monitor the amplitude and frequency of the acoustic wave; The optical fiber strain sensor is used to be deployed in the source area of the debris flow channel, placed horizontally and parallel to the slope to locate the collapsed material; The "double fishbone" optical fiber monitoring network construction module is used to form a monitoring plan based on basic geological information, and deploy a "double fishbone" optical fiber monitoring network along both sides of the debris flow channel according to the monitoring plan; The background data determination module is used to collect environmental parameters of the area to be monitored to form a background database; it is also used to preset a temperature difference threshold ΔT0 and an amplitude difference threshold ΔP0; The temperature start judgment module is used to determine the air temperature T in the background database at the i-th moment. a (i) and the lowest level temperature T1(i) of the temperature sensor in the optical fiber monitoring network, calculate ΔT(i) = T1(i)- T a (i); When |ΔT(i)|≥ΔT0, it is determined that the debris flow has started at time i and the mud and water level calculation module is started; otherwise, the monitoring at the next time is executed; The mud level calculation module is used to extract the temperature of the temperature sensor at each level, which is T1, ..., T k ,…,T H , when T k (i)-T k When (i-1)≠0, the 1st to kth temperature sensors are active sensors; according to the spacing and number of active sensors, the mud water level height value and the current rising rate value ΔH(i) are determined; The collapse object determination and counting module is used to determine whether there is collapse object at the position q where the strain sensor is arranged according to the strain sensor; if there is collapse object, the collapse object is counted and recorded as N q ; If it does not exist, then N q =0; The acoustic foreign body determination module is used to calculate the change in the acoustic amplitude of the first acoustic sensor on either side of the debris flow channel from the i-1th moment to the i-th moment ΔP(i) = P 11 (i)- P 11 (i-1); if ΔP(i) ≥ ΔP0, it is determined that there is foreign matter in the debris flow channel, and the acoustic wave start-up judgment module is activated; if ΔP(i) < ΔP0, it is determined that there is no foreign matter in the debris flow channel, and the monitoring at the next moment is performed; The acoustic wave start determination module is used to simultaneously collect the acoustic wave characteristics F of the first acoustic wave sensor on the left side and the first acoustic wave sensor on the right side of the debris flow channel. 11 and F 21 If F 11 and F 21 If the F 11 and F 21 If there is no match, it is determined that the debris flow has not occurred and the monitoring at the next moment is performed; The flow velocity calculation module is used to collect the monitoring signal time difference t from the first acoustic wave sensor to the second acoustic wave sensor on either side of the debris flow channel, calculate the flow velocity s=L1 / t of the debris flow as the debris flow velocity monitored by the first acoustic wave sensor, where L1 is the distance between the installation location of the first acoustic wave sensor and the installation location of the second acoustic wave sensor, and use the same method to calculate the debris flow velocity monitored by all acoustic wave sensors, and calculate the average flow velocity S of the debris flow; The warning module is used to issue a debris flow warning based on the mud and water level height value, the rising rate value, the location and count of the collapsed objects, the debris flow velocity and the average flow velocity; and the warning situation is divided into four levels; specifically, the following steps are performed: Step S81: determine the change of the difference ΔH(i) between the mud water level value H(i) at the current time i and the mud water level value H(i-1) at the time i-1. If 0<ΔH(i)≤H v , and H(i)≤H e , it is judged that the mud water level is rising, but it is a normal water level cycle change and no warning is issued; among them, H v is the mud water level rising rate threshold, H e is the mud water level height threshold; Step S82: If 0<ΔH(i)≤H v And H e <H(i), it is judged that the mud water level is rising, exceeding the historical normal water level and rising rate, which is likely to cause flood disasters, and a level 1 warning is issued; Step S83, if H v <ΔH(i), and H e <H(i), it is judged that the mud and water level is rising rapidly and is likely to cause mud and rock flow in the short term, and a level 2 warning is issued; if H v <ΔH(i) and H e <H(i) and the number of caving materials in the provenance area is N q ≥Q, where Q is the threshold for the amount of landslide debris. This indicates that the debris flow source is abundant and the conditions for a debris flow outbreak are met, and a Level 3 warning is issued. Step S84, if H v <ΔH(i) and H e <H(i) and identify the sound wave enhancement in the debris flow channel, judge that the debris flow is erupting, issue a fourth-level warning, calculate the arrival time of the debris flow based on the average flow velocity S of the debris flow and the total length L of the debris flow channel, send warning information to the public through multimedia, and give time to avoid danger.

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