Elastic fiber optic, time-of-flight sensor for long distance landslide monitoring with sub-mm precision

Abstract

Disclosed are systems and methods that employ elastic fiber optic, time-of-flight sensors for long distance landslide monitoring with sub-mm precision. The time-of-flight (ToF) sensor is integrated in conjunction with a single-photon avalanche diode (SPAD). By coupling both the emission source and the detector with a stretchable optical fiber, our inventive systems and methods continuously monitor the length of the stretchable optical fiber by measuring a traveling time of an optical pulse traversing the stretchable optical fiber. A significant, detectable change in the length of the stretchable optical fiber – indicative of ground movement or deformation, triggers an alarm, providing an early warning for potential landslides. As such, systems and methods according to aspects of the present disclosure provide a reliable, sensitive, precise, cost-effective, real-time solution for landslide detection and monitoring – a problem that has plagued the art.

Description

ELASTIC FIBER OPTIC, TIME-OF-FLIGHT SENSOR FOR LONG DISTANCE LANDSLIDE MONITORING WITHSUB-MM PRECISIONFIELD

[0001] This application relates generally to landslide monitoring. More particularly, it pertains to fiber optic, time-of-flight sensors for long distance landslide monitoring with sub-mm precision.BACKGROUND

[0002] As those skilled in the art will understand and appreciate, landslides are a significant and recurring issue in many regions of the world, posing threats to human life, property, infrastructure, and the environment. Problems resulting from landslides are particularly acute in areas with steep terrain, loose soil, and heavy rainfall, where traditional methods of protection may be inadequate or overly expensive. The lack of efficient and cost-effective measures for landslide protection has created an urgent need for innovative solutions to this most important problem.SUMMARY

[0003] An advance in the art is made according to aspects of the present disclosure directed to systems and methods that employ elastic fiber optic, time-of-flight sensors for long distance landslide monitoring with sub-mm precision.

[0004] In sharp contrast to the prior art, systems and methods according to aspects of the present disclosure employ a time-of-flight (ToF) sensor in conjunction with a single-photon avalanche diode (SPAD). By coupling both the emission source and the detector with a stretchable optical fiber, systems and methods according to aspects of the present disclosure continuously monitor the length of the stretchable optical fiber by measuring a traveling time of an optical pulse traversing the stretchable optical fiber.

[0005] According to an aspect of the present disclosure, a significant, detectable change in the length of the stretchable optical fiber - indicative of ground movement or deformation, triggers an alarm, providing an early warning for potential landslides. As such, systems and methods according toaspects of the present disclosure provide a reliable, sensitive, precise, cost-effective, real-time solution for landslide detection and monitoring - a problem that has plagued the art.

[0006] As we shall show and describe our inventive systems and methods according to aspects of the present disclosure significantly advance the state of the art of landslide prevention and detection by introducing several inventive features.

[0007] First, our inventive ToF SPAD Integration: i) utilizes a ToF sensor to accurately measure the length of the stretchable optical fiber; ii) incorporates a SPAD to enhance sensitivity and detection capabilities; and iii) the integration of ToF with the SPAD advantageously provides real-time monitoring and rapid response to changes in fiber length.

[0008] Second, our inventive optical fiber coupling to an emission source and detector: i)employs an optical fiber to encapsulate both the emission source and the detector, ensuring consistent and controlled measurements; ii) the entire length of the optical fiber is continuously monitored, and any significant alteration in length triggers an alarm; and iii) the sensitivity of the optical fiber to length changes provides a direct nexus to ground movement, allowing for early detection of potential landslides.

[0009] Finally, our inventive alarm system: i) Alarm System: integrates an alarm system that is activated once a significant change in the fiber's length is detected; and ii) the alarm system provides an immediate alert mechanism, enabling timely evacuation or intervention to mitigate the risks associated with landslides.

[0010] As those skilled in the art will readily understand and appreciate when compared to global positioning system-based systems and methods - our inventive systems and methods according to aspects of the present disclosure exhibit i) high precision, and ii) scalable deployment.

[0011] High precision is achieved as the innovative ToF sensor and SPAD integration provides millimeterlevel accuracy when measuring changes in optical fiber length, and that accuracy can be further improved to sub-mm range by increasing integration time. Scalable deployment allows for the centralized placement of ToF sensors while distributing the optical fiber across large-scale geographies - including slopes; and a centralized sensor placement simplifies maintenance and datacollection, making the system more cost-effective and efficient for large-area monitoring. Systems and methods according to aspects of the present invention exhibit structure and features that collectively provide a robust solution to the problem of landslide protection, offering a novel approach that leverages advanced sensing technology to deliver precise and timely warnings.BRIEF DESCRIPTION OF THE DRAWING

[0012] FIG. 1 is a schematic diagram and photo illustration showing an illustrative landslide according to aspects of the present disclosure.

[0013] FIG. 2 is a schematic flow diagram showing illustrative features and their relationship and / or sequence as performed by illustrative systems and methods according to aspects aspects of the present disclosure.

[0014] FIG.3 is a schematic diagram showing an illustrative single displacement sensor in a transmission configuration and support circuitry according to aspects of the present disclosure.

[0015] FIG. 4 is a plot of Allen Deviation (mm) vs Averaging Time Tau (s) of an Allen deviation plot for a field test of systems and methods according to aspects of the present disclosure and their relationship or sequence according to aspects of the present disclosure.

[0016] FIG. 5 is a schematic diagram showing illustrative optical fiber burying for systems and methods according to aspects of the present disclosure.

[0017] FIG. 6 is a schematic diagram of an illustrative mullti-sensor system according to aspects of the present disclosure.

[0018] FIG. 7 is a schematic flow diagram of an illustrative computing system that may be employed in and execute operations associated with systems and methods according to aspects of the present disclosure.DETAILED DESCRIPTION

[0019] The following merely illustrates the principles of this disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope.

[0020] Furthermore, all examples and conditional language recited herein are intended to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions.

[0021] Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

[0022] Thus, for example, it will be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the disclosure.

[0023] Unless otherwise explicitly specified herein, the FIGs comprising the drawing are not drawn to scale.

[0024] FIG. 1 is a schematic diagram and photo illustration showing an illustrative landslide according to aspects of the present disclosure.

[0025] By way of some additional background, we again note that landslides are a significant and recurring issue in many regions, posing threats to human lives, property, infrastructure, and the environment. The problem presented by landslides is particularly acute in areas with steep terrain, loose soil, and heavy rainfall, where traditional methods of protection may be inadequate or overly expensive. Existing solutions to landslide prediction and prevention often fail to providecomprehensive, long-term stability, leading to ongoing risks and damage. The lack of efficient and cost-effective measures for landslide protection has created an urgent need for innovative solutions to safeguard communities and critical infrastructure from these devastating natural events.

[0026] According to the sliding speed of landslides, landslides are divided into four categories: i) Peristaltic landslides, whose movement is difficult to see with the naked eye and can only be discovered through instrument observation; ii) Slow landslides: sliding from a few centimeters to tens of centimeters per day , people can directly observe the activities of landslides with the naked eye; iii) Medium-speed landslides: landslides that slide tens of centimeters to several meters per hour; and iv) High-speed landslides: landslides that slide several meters to tens of meters per second.

[0027] Common landslide prediction / prevention methods used in the field, as interpreted from a variety of significant research papers, include:

[0028] Gravity Measurement Method: Monitors changes in gravitational forces in potential landslide areas.

[0029] Special Geodetic Measurement Method: Utilizes specialized geodetic instruments to measure ground deformations.

[0030] Groundwater Monitoring Method: Measures groundwater levels and pressure to assess landslide risk.

[0031] Liquid Static Level Measurement: Utilizes liquid levels to detect ground movements.

[0032] Conventional Geodetic Measurement Method: Employs traditional geodetic tools to monitor ground deformations.

[0033] Underground Drilling Inclination Method: Measures inclination in underground drill holes to detect ground movement.

[0034] Close-Range Photogrammetry Method: Uses close-range photography to create detailed topographical maps.

[0035] These methods, while valuable in assessing landslide risks, share common disadvantages. They are often affected by climatic conditions and terrain, hindering continuous monitoring. The automation level is generally low, requiring substantial human intervention. Additionally, the data is often challenging to process in a timely manner, and the monitoring cycles are lengthy. These limitations highlight the need for innovative solutions such as those according to aspects of the present disclosure that can provide continuous, automated, and real-time monitoring of landslide- prone areas.

[0036] While GPS-based methods have been employed for real-time landslide detection, they exhibit significant limitations in terms of accuracy (sub cm) and scalability. Civilian GPS systems often lack a precision required for early landslide detection, and their accuracy can be further compromised by factors such as atmospheric conditions and signal obstructions. Moreover, implementing GPS monitoring on a large scale requires substantial communication infrastructure, which can be challenging and costly to establish and maintain in landslide-prone areas.

[0037] Systems and methods according to aspects of the present disclosure address the problem of landslide protection by utilizing the Time-of-Flight (ToF) sensor in conjunction with a Single-Photon Avalanche Diode (SPAD). By coupling both the emission source and the detector with a stretchable optical fiber (shown illustratively in FIG. 2), system and methods according to aspects of the present disclosure continuously monitor the entire length of the optical fiber by measuring a travel time (the ToF) of an optical pulse to traverse the length of the optical fiber. Any significant change in the length of the optical fiber - indicative of ground movement or deformation - triggers an alarm, providing an early warning for potential landslides. As a result, systems and methods according to aspects of the present disclosure advance the state of the art by offering a precise, cost-effective, and real-time solution for landslide detection and monitoring.

[0038] As we shall show and describe our inventive systems and methods according to aspects of the present disclosure significantly advance the state of the art of landslide prevention and detection by introducing several inventive features.

[0039] First, our inventive ToF SPAD Integration: i) utilizes a ToF sensor to accurately measure the length of the stretchable optical fiber; ii) incorporates a SPAD to enhance sensitivity and detection capabilities; and iii) the integration of ToF with the SPAD advantageously provides real-time monitoring and rapid response to changes in fiber length.

[0040] Second, our inventive optical fiber coupling to an emission source and detector: i)employs an optical fiber to encapsulate both the emission source and the detector, ensuring consistent and controlled measurements; ii) the entire length of the optical fiber is continuously monitored, and any significant alteration in length triggers an alarm; and iii) the sensitivity of the optical fiber to length changes provides a direct nexus to ground movement, allowing for early detection of potential landslides.

[0041] Finally, our inventive alarm system: i) Alarm System: integrates an alarm system that is activated once a significant change in the fiber's length is detected; and ii) the alarm system provides an immediate alert mechanism, enabling timely evacuation or intervention to mitigate the risks associated with landslides.

[0042] As those skilled in the art will readily understand and appreciate when compared to global positioning system-based systems and methods - our inventive systems and methods according to aspects of the present disclosure exhibit i) high precision, and ii) scalable deployment.

[0043] High precision is achieved as the innovative ToF sensor and SPAD integration provides millimeterlevel accuracy when measuring changes in optical fiber length, and that accuracy can be further improved to sub-mm range by increasing integration time. Scalable deployment allows for the centralized placement of ToF sensors while distributing the optical fiber across large-scale geographies - including slopes; and a centralized sensor placement simplifies maintenance and data collection, making the system more cost-effective and efficient for large-area monitoring. Systems and methods according to aspects of the present invention exhibit structure and features thatcollectively provide a robust solution to the problem of landslide protection, offering a novel approach that leverages advanced sensing technology to deliver precise and timely warnings.

[0044] FIG. 2 is a schematic flow diagram showing illustrative features and their relationship and / or sequence as performed by illustrative systems and methods according to aspects aspects of the present disclosure.

[0045] Sensor with Time-of-Flight Lidar and Stretchable fiber

[0046] FIG.3 is a schematic diagram showing an illustrative single displacement sensor in a transmission configuration and support circuitry according to aspects of the present disclosure.

[0047] Evaluate the measurement accuracy of the designed sensor

[0048] For experimental configurations evaluations, the averaged refractive index for optical fiber employed in our systems is 1.48980. The ToF measurement variation against the averaged value is + / - 2mm in free space measurement. This translates to around + / -l-3mm actual fiber length measurement variation on 4000mm measured distance for 2 hours from our previous configurations evaluated.

[0049] Validate the feasibility of long-distance measurements using another ToF sensor

[0050] Because landside protection needs long coverage, we need to determine the feasibility of longdistance measurement by ToF. Our state-of-the-art monolithic ToF sensor can operate over 100 meters. In the case of free-space applications, the upper limit of the detection range is determined by power of the illuminator, sensitivity of the SPAD, ambient light condition as well as the upper limit of timing circuitry. For fiber optic version of TOF sensor, however, the effects of the first three factors are significantly reduced. By employing customized timing circuitry, it is feasible to further elongate the range that the sensor can cover.

[0051] Assess the sensor's stability over time using the Allan variation method

[0052] We need to estimate the measurement stability of our inventive systems and methods according to aspects of the present disclosure device over time. At the same time, the best alarm solution should be sought based on the characteristics of landslides and the stability of the equipment employed. We use Allan variation techniques to measure this aspect. We used VL53L4CX STM32 light for uninterrupted measurement within 48 hours, collected distance data every 250ms, and calculated the Overlapping Allan Deviation of the data, which is shown in FIG. 4, which is a plot of Allen Deviation (mm) vs Averaging Time Tau (s) of an Allen deviation plot for a field test of systems and methods according to aspects of the present disclosure and their relationship or sequence according to aspects of the present disclosure.

[0053] Typically, we can average out the noise by making multiple measurements and estimate the mean value. When such techniques are employed, we can reduce the variance of the reading. If system noise is purely white noise, measurement variance will be proportional inversely to square root of N, the number of the measurements.

[0054] However, physical systems also have other sources of noise, for example ^noise. As the duration of observation increases, color noise -^-noise becomes dominant. As a result, further increasing the f observation time will not improve the performance of measurement. Allan variance analysis can be used to estimate the optimal observation time when the white noise reaches the same level of color noise and the variance plot deviate from 1 / V / V law.

[0055] FIG. 4 shows the Allan deviation plot for a ToF sensor. The optimal observation period is about110 seconds. In this observation period, the lowest detection limit is estimated in the scale of submm.

[0056] Practical Deployment Scheme

[0057] Consider a slope that is 500 meters long and 100 meters high with a slope angle between 20 and35 degrees, with a history of landslide activity. To effectively monitor this slope using the ToF sensorand stretchable fiber-optic system according to aspects of the present disclosure, the following deployment scheme can be implemented:

[0058] FIG. 5 is a schematic diagram showing illustrative optical fiber burying for systems and methods according to aspects of the present disclosure.

[0059] FIG. 6 is a schematic diagram of an illustrative mullti-sensor system according to aspects of the present disclosure.

[0060] Fiber-optic cable layout

[0061] Install the stretchable fiber-optic cable in a grid pattern across the slope, with a spacing of 20 meters between each parallel line as shown in FIG. 6.

[0062] Bury the fiber-optic cable at a depth of 50 cm to 1 meter, depending on the soil conditions and expected depth of potential landslide planes as illustratively shown in FIG. 5.

[0063] Secure the fiber-optic cable to the ground using anchors or stakes at regular intervals to ensure that any ground movement is effectively transferred to the cable.

[0064] ToF sensor placement

[0065] Place the ToF sensors at the base of the slope, where they can be easily accessed for maintenance and data collection.

[0066] Install one ToF sensor for every 100 meters of fiber-optic cable, allowing each sensor to monitor a specific section of the slope.

[0067] Protect the ToF sensors from environmental factors such as rain, wind, and debris by housing them in weatherproof enclosures.

[0068] Data transmission and communication

[0069] Connect the ToF sensors to a central data processing unit using wireless communication technology, such as LoRaWAN or Wi-Fi, depending on the distance and terrain.

[0070] Employ a mesh network topology to ensure reliability, even if one or more nodes fail and redundant sensing node will take place.

[0071] Transmit sensor data to the central processing unit at regular intervals (250ms one point and use the average of 2 mins' data) for real-time monitoring and analysis.

[0072] Power supply

[0073] Each ToF sensor will equippied with a solar panel and rechargeable battery to ensure continuous operation without the need for frequent battery replacements.

[0074] Install larger solar panels and backup power systems at the central data processing unit to maintain uninterrupted operation during prolonged periods of inclement weather.

[0075] Alarm system

[0076] Set up an alarm system that triggers when the fiber-optic cable elongation exceeds a predetermined threshold, indicating potential ground movement.

[0077] Implement multiple alarm thresholds to distinguish between minor soil settling and more significant landslide events.

[0078] Configure the alarm system to send notifications to relevant authorities and affected communities through SMS, email, or a dedicated mobile application.

[0079] Maintenance and calibration

[0080] Conduct regular maintenance checks on the fiber-optic cables, ToF sensors, and communication infrastructure to ensure optimal performance.

[0081] Perform periodic calibration of the ToF sensors to maintain accurate measurements and compensate for any drift over time.

[0082] By implementing this deployment scheme, the landslide monitoring and early warning system can effectively cover the entire slope, providing real-time data on ground movement and enabling timely alerts in case of potential landslides. The modular nature of the system allows for easy expansion or adaptation to other slopes with different dimensions and characteristics.

[0083] Landslide Monitoring and Early Warning System:

[0084] Considering the soil mechanics principles and real-world scenarios, the following deployment scheme is proposed for a landslide monitoring and early warning system using fiber-optic sensors over a 100-meter range.

[0085] Slope angle and soil type

[0086] System and methods according to aspects of the present disclosure are designed for slopes with an angle between 20 and 35 degrees, which are considered to be at a higher risk of landslides.

[0087] The soil type in a monitored area is assumed to be a mixture of loose soil, weathered rock, and semi-rock layers, which have lower shear strength and are more susceptible to deformation and sliding.

[0088] Fiber-optic sensor layout

[0089] Fiber-optic sensors are installed in a grid pattern across the slope, with a spacing of 10 to 20 meters between each parallel line, depending on slope heterogeneity and the desired level of monitoring resolution.

[0090] The sensors are buried at a depth of 0.5 to 1 meter, which is considered to be within the range of potential slip surfaces for most shallow to medium-depth landslides.

[0091] Alarm thresholds and time frame

[0092] The alarm thresholds are set based on the expected rate of soil movement and the potential for rapid landslide development.

[0093] A two-tier alarm system is implemented

[0094] Tier 1 (Early Warning): If the fiber-optic sensors detect a cumulative soil movement of 50 mm or more within a 7-day period, a Tier 1 alarm is triggered. This threshold indicates a slow-moving landslide, which requires close monitoring and preparedness measures.

[0095] Tier 2 (Imminent Landslide): If the fiber-optic sensors detect a cumulative soil movement of 100 mm or more within a 24-hour period, a Tier 2 alarm is triggered. This threshold indicates a rapidly accelerating landslide, which requires immediate evacuation and emergency response measures.

[0096] Data transmission and processing

[0097] The fiber-optic sensors continuously transmit data to a central processing unit, which analyzes the data in real-time using advanced algorithms to detect changes in soil movement patterns.

[0098] Computer / data processing circuitry and / or programming filters out noise and compensates for environmental factors, such as temperature fluctuations, to ensure accurate and reliable measurements.

[0099] Integration with other monitoring systems

[0100] The fiber-optic sensor-based landslide monitoring system is integrated with other monitoring technologies, such as rainfall gauges, piezometers, and inclinometers, to provide a comprehensive assessment of the slope's stability.

[0101] The data from these complementary monitoring systems are used to validate and refine the alarm thresholds and to improve the overall accuracy and reliability of the landslide early warning system.

[0102] Maintenance and calibration

[0103] Regular maintenance and calibration of the fiber-optic sensors and data processing unit are conducted to ensure optimal performance and to minimize drift over time.

[0104] The alarm thresholds are periodically reviewed and adjusted based on the historical data and any changes in the slope's conditions or land use patterns.

[0105] By implementing this deployment scheme, the landslide monitoring and early warning system can effectively detect slow-moving and rapidly accelerating landslides, providing timely warnings to authorities and affected communities. The integration of fiber-optic sensors with other monitoring technologies ensures a robust and reliable assessment of the slope's stability, enabling informed decision-making and risk mitigation strategies.

[0106] FIG. 7 is a schematic block diagram of an illustrative computer system in which aspects of the present disclosure may be executed to produce methods / algorithms according to aspects of the present disclosure.

[0107] As may be immediately appreciated, such a computer system may be integrated into another system such as a router and may be implemented via discrete elements or one or more integrated components. The computer system may comprise, for example, a computer running any of several operating systems. The above-described methods of the present disclosure may be implemented on the computer system 700 as stored program control instructions.

[0108] Computer system 700 includes processor 710, memory 720, storage device 730, and input / output structure 740. One or more input / output devices may include a display. One or more busses 750 typically interconnect the components, 710, 720, 730, and 740. Processor 710 may be a single or multicore. Additionally, the system may include accelerators etc., further comprising the system on a chip.

[0109] Processor 710 executes instructions in which embodiments of the present disclosure may comprise steps described in one or more of the Drawing figures. Such instructions may be stored in memory 720 or storage device 730. Data and / or information may be received and output using one or more input / output devices.

[0110] Memory 720 may store data and may be a computer-readable medium, such as volatile or nonvolatile memory. Storage device 730 may provide storage for system 700 including for example, the previously described methods. In various aspects, storage device 730 may be a flash memory device, a disk drive, an optical disk device, or a tape device employing magnetic, optical, or other recording technologies.

[0111] Input / output structures 740 may provide input / output operations for system 700.

[0112] While we have presented our inventive concepts and description using specific examples, our invention is not so limited. Accordingly, the scope of our invention should be considered in view of the following claims.

Claims

Claims1. A landslide monitoring system comprising: an integrated sensor having a light emitter connected to one end of a stretchable optical fiber and a light receiver connected to the other end of the stretchable optical fiber, the stretchable optical fiber located across a slope of a terrain; circuitry configured to operate the emitter and receiver and determine if the stretchable optical fiber stretches beyond a pre-determined amount; and generate an alarm when the stretchable optical fiber stretches beyond the predetermined amount; wherein the alarm is a landslide warning.

2. The system of claim 1 wherein the integrated sensor is a time-of-flight sensor.

3. The system of claim 2 wherein the light receiver includes a single-photon-avalanche diode (SPAD).

4. The system of claim 3 wherein the light emitter, the light receiver, and ends of the stretchable optical fiber are encapsulated together.

5. The system of claim 2 comprising a plurality of individual integrated sensors, each individual one of the plurality of individual integrated sensors connected to a respective one of a plurality of individual stretchable optical fibers.

6. The system of claim 5 wherein the plurality of individual stretchable optical fibers are arranged along the slope in a pre-determined pattern.

7. The system of claim 6 wherein the plurality of individual optical fibers are arranged to be substantially parallel to one another.

8. The system of claim 7 wherein the plurality of individual optical fibers are at least partially buried, and the integrated sensors are not.

9. The system of claim 8 wherein the integrated sensors are all located at a base of the slope.

10. The system of claim 9 wherein at least one integrated sensor is connected to every 100 meters of individual optical fiber.

11. The system of claim 8 configured to exhibit a millimeter-level accuracy in measuring changes in optical fiber length.

12. The system of claim 11 configured to exhibit sub-millimeter-level accuracy in measuring changes in optical fiber length.

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