Water and soil loss online monitoring system and method based on optical frequency domain reflection

Abstract

The invention discloses a water and soil loss online monitoring system and method based on optical frequency domain reflection, the system comprises an optical fiber detection unit, an optical frequency domain reflection demodulation unit and a data processing unit, the optical fiber detection unit can be placed in to-be-measured soil to measure the to-be-measured soil; the optical frequency domain reflection demodulation unit is used for obtaining Rayleigh scattering signals in the distributed optical fibers and obtaining stress distribution data of the distributed optical fibers through demodulation; the data processing unit is used for determining an interface stress abrupt change position of the to-be-detected soil and air and calculating to obtain the water and soil loss amount of the to-be-detected soil; the data processing unit is also used for calculating the humidity distribution and humidity gradient of the soil to be detected and evaluating the water and soil loss risk of the soil to be detected. According to the method, the variable quantity of the soil and air interface can be accurately judged, the water and soil loss quantity can be quantified, the distribution of the soil humidity along the depth and the humidity gradient can be calculated by combining the correlation between the stress and the humidity, and the water and soil loss risk of the soil is evaluated and early warned.

Description

Technical Field

[0001] The invention belongs to the technical field of soil and water monitoring and analysis, and in particular relates to an online soil and water loss monitoring system and method based on optical frequency domain reflection. Background Art

[0002] Soil erosion is one of the important environmental issues. It not only poses a serious threat to agricultural production and ecosystem balance, but may also trigger a series of geological disasters, such as debris flows and landslides. Therefore, how to efficiently and accurately monitor the process of soil erosion and its influencing factors has become an important research direction in the field of soil and water conservation and land resource management. Traditional soil erosion monitoring methods mainly rely on manual observation or indirect estimation, which makes it difficult to grasp the dynamic process of soil erosion in real time. At the same time, the monitoring range is limited and the accuracy is insufficient, which cannot meet the needs of complex terrain and changing environmental conditions.

[0003] As an improvement, currently, fiber optic sensing technology has received extensive attention in the field of soil mechanics and environmental monitoring due to its high sensitivity, distributed monitoring capabilities and environmental adaptability. However, although fiber optic sensing technology has been applied to structural health monitoring, geological disaster warning and other fields, its application in soil and water loss monitoring is still not perfect.

[0004] The dynamic process of soil erosion is affected by many factors, including soil moisture, rainfall intensity, and surface cover conditions. Among them, soil moisture is an important factor affecting soil structural stability and anti-erosion ability. The increase in soil moisture usually leads to a weakening of the bonding force between soil particles, which in turn causes soil loosening and a significant reduction in stress. In addition, the gradient change in soil moisture will increase the risk of local water erosion, becoming one of the key causes of soil erosion. Therefore, in soil erosion monitoring, it is necessary not only to monitor the amount of erosion on the soil surface, but also to combine the dynamic changes in soil moisture to assess the potential risk of soil erosion. At present, distributed fiber optic sensing technology is used in the monitoring of soil erosion. Because it cannot comprehensively consider the various states of the soil, and the data collection and processing methods are not reasonable, the accuracy of soil monitoring and analysis needs to be further improved. Summary of the invention

[0005] The present invention provides an online monitoring system and method for soil erosion based on optical frequency domain reflection, aiming to solve the problem that the accuracy of soil monitoring and analysis needs to be further improved due to the inability to comprehensively consider various soil states and unreasonable data collection and processing methods in the current distributed optical fiber sensing technology used in soil erosion monitoring.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme: An online monitoring system for soil and water loss based on optical frequency domain reflection comprises an optical fiber detection unit, an optical frequency domain reflection demodulation unit and a data processing unit, wherein: The optical fiber detection unit includes an optical fiber detection part, which includes a measuring rod and a distributed optical fiber located on the outer wall of the measuring rod, and the outer side of the distributed optical fiber has a protective layer; at least a part of the optical fiber detection unit can be placed in the soil to be tested so as to measure the soil to be tested; The optical frequency domain reflection demodulation unit is connected to the distributed optical fiber; the optical frequency domain reflection demodulation unit is used to obtain the Rayleigh scattering signal in the distributed optical fiber, and obtain the stress distribution data of the distributed optical fiber through frequency domain demodulation; The data processing unit is used to determine the position of the interface stress mutation between the soil to be tested and the air according to the stress distribution data, and calculate the amount of soil and water loss of the soil to be tested by the change of the interface stress mutation position; The data processing unit is also used to calculate the moisture distribution and moisture gradient of the soil to be tested, generate real-time warning signals based on the moisture distribution and moisture gradient, and evaluate the soil erosion risk of the soil to be tested.

[0007] In some embodiments, in the optical frequency domain reflectometry demodulation unit, the relationship between the frequency of the optical signal injected into the distributed optical fiber and the length of the optical propagation path in the distributed optical fiber is as follows: (1); in, is the frequency difference, is the frequency modulation rate of the optical signal, is the geometric position change of the scattering point in the distributed optical fiber; The relative change of the phase change of the scattered signal and the fiber length is as follows (2): (2); in, is the phase change of the Rayleigh scattering signal, is the effective refractive index of the optical fiber, is the wavelength of the injected optical signal. Combined with the definition of strain, the relationship between the distributed optical fiber strain and the Rayleigh scattering phase change is obtained as follows: (3); in, is the strain of the distributed optical fiber; The phase change is detected by optical frequency domain reflection and the strain distribution of the optical fiber is calculated.

[0008] In some embodiments, the data processing unit determines the position of the sudden change in interfacial stress between soil and air, and calculates the amount of soil and water loss of the tested soil by the change in the position of the sudden change in interfacial stress, specifically including: The position of the soil-air interface corresponds to the mutation point in the optical fiber stress distribution, and its position satisfies the extreme value condition of the stress change rate: (4); in, is the stress change rate, is stress, is the position variable of the soil-air interface, is the position of the soil-air interface, is the set interface mutation judgment threshold.

[0009] In some embodiments, the data processing unit has a moisture distribution measurement module, which can calculate the moisture distribution and moisture gradient of the soil to be tested based on the stress distribution data of the distributed optical fiber monitoring and the soil moisture relationship model.

[0010] Furthermore, the soil moisture relationship model adopts the following formula (5): (5); in, is the moisture distribution of the soil to be tested, is the stress in dry soil state, is the soil moisture distribution, is the humidity influencing factor.

[0011] Furthermore, the moisture gradient of the soil to be tested is expressed as the following formula (6): (6); in, is the moisture gradient of the soil to be tested, For external stress.

[0012] Furthermore, when the soil moisture gradient exceeds a preset threshold, the moisture distribution measurement module can generate a soil erosion risk warning signal based on the following formula (7): (7); in, is a risk factor, and is an empirical coefficient related to soil type and environmental conditions, is the humidity gradient; when >Risk Threshold R th When the humidity distribution measurement module triggers the soil and water loss risk warning signal.

[0013] Furthermore, a plurality of optical fiber detectors are provided, and the burial depths of the plurality of optical fiber detectors are adjusted and confirmed according to the soil type and monitoring requirements. The plurality of optical fiber detectors are inserted according to preset positions in the monitoring area so as to form a monitoring network.

[0014] Furthermore, the distributed optical fiber is fixed to the outer wall of the probe in an embedded manner, and the protective layer includes a polymer protective coating located on the distributed optical fiber.

[0015] The present invention also discloses an online monitoring method for soil and water loss based on optical frequency domain reflection. The method is based on the above-mentioned online monitoring system for soil and water loss based on optical frequency domain reflection and comprises the following steps: S1. Insert the optical fiber detector into the soil of the monitoring area and adjust the burial depth and layout density; S2, the optical frequency domain reflection demodulation unit collects the Rayleigh scattering signal in the distributed optical fiber, performs frequency domain demodulation, and obtains the stress distribution data of the optical fiber along the length direction; S3. The data processing unit analyzes the stress distribution data, identifies the location of stress mutation, determines the dynamic position of the interface between the tested soil and the air, calculates the amount of soil erosion, calculates the moisture distribution and moisture gradient of the tested soil, evaluates the potential risk of soil erosion, and generates a warning signal according to a preset threshold.

[0016] Compared with the prior art, the online monitoring system and method of soil and water loss based on optical frequency domain reflection of the present invention has the following beneficial effects: The present invention discloses an online monitoring system for soil and water loss based on optical frequency domain reflection. By inserting an optical fiber detection unit into the soil, real-time perception and positioning of stress distribution changes can be achieved. Based on the stress mutation point perceived by the optical fiber, the position of the soil-air interface and its change amount can be accurately judged, thereby quantifying the amount of soil and water loss. At the same time, combined with the correlation between stress and humidity, the system can calculate the distribution of soil moisture along the depth and the humidity gradient, evaluate the soil and water loss risk of the soil, and provide a risk warning function. By combining the optical frequency domain reflection technology with soil moisture monitoring, the present invention can not only monitor the actual occurrence of soil and water loss, but also predict the potential risk of soil and water loss through changes in soil moisture gradient. It provides a relatively effective monitoring method for soil and water conservation, which has certain practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings in the specification are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0018] Figure 1 This is a schematic diagram of the overall principle architecture of an online monitoring system for soil and water loss based on optical frequency domain reflection according to the present invention; Figure 2 It is a schematic diagram of the principle of optical frequency domain reflection in an online soil and water loss monitoring system based on optical frequency domain reflection of the present invention; Figure 3 It is a schematic diagram of soil / air interface stress changes in an online soil and water loss monitoring method based on optical frequency domain reflection of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0022] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0023] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0024] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] How to improve the monitoring of the actual occurrence of soil erosion and predict the potential risk of soil erosion through changes in soil moisture gradient.

[0026] The present invention discloses an online monitoring system for soil and water loss based on optical frequency domain reflection, comprising an optical fiber detection unit, an optical frequency domain reflection demodulation unit and a data processing unit, wherein: The optical fiber detection unit includes an optical fiber detection part, which includes a measuring rod and a distributed optical fiber located on the outer wall of the measuring rod, and the outer side of the distributed optical fiber has a protective layer; at least a part of the optical fiber detection unit can be placed in the soil to be tested so as to measure the soil to be tested; The optical frequency domain reflection demodulation unit is connected to the distributed optical fiber; the optical frequency domain reflection demodulation unit is used to obtain the Rayleigh scattering signal in the distributed optical fiber, and obtain the stress distribution data of the distributed optical fiber through frequency domain demodulation; The data processing unit is used to determine the position of the interface stress mutation between the soil to be tested and the air according to the stress distribution data, and calculate the amount of soil and water loss of the soil to be tested by the change of the interface stress mutation position; The data processing unit is also used to calculate the moisture distribution and moisture gradient of the soil to be tested, generate real-time warning signals based on the moisture distribution and moisture gradient, and evaluate the soil erosion risk of the soil to be tested.

[0027] The online soil and water loss monitoring system of the present invention establishes a connection with a distributed optical fiber through an optical frequency domain reflectometer, and can obtain stress distribution changes along the length of the optical fiber; the data processing unit determines the soil-air interface according to the stress mutation position in the distributed optical fiber, and calculates the amount of soil and water loss through the change in the interface position; the humidity distribution measurement module calculates the distribution of soil moisture along the depth based on the stress measurement value near the interface, and evaluates the soil and water loss risk through the humidity gradient, which can realize accurate monitoring of soil and water loss, dynamic tracking of humidity distribution and risk assessment, and provide technical support for soil and water conservation and soil management.

[0028] Specifically, if Figure 1As shown, the present invention utilizes the high sensitivity of Rayleigh scattering and the high-resolution characteristics of optical frequency domain demodulation to realize dynamic perception and positioning of stress distribution in soil, and accurately calculates the amount of soil and water loss by analyzing the stress mutation position, soil moisture distribution and its gradient, evaluates the risk of soil and water loss, and generates real-time early warning signals. The system includes a metal probe, an embedded optical fiber, an optical frequency domain demodulation module and a data processing module. The metal probe is a sensor carrier, and the outer wall is embedded with an optical fiber, part of which is inserted into the soil, and the other part is exposed to the air, which is used to sense the stress distribution changes near the soil-air interface. The metal probe is made of high-strength materials, which can provide stable mechanical support and ensure the reliable transmission of optical fiber sensing signals. At the same time, the burial depth of the metal probe can be adjusted to meet the monitoring requirements of different soil types, depths and environmental conditions. The optical fiber is a single-mode optical fiber, and the outer fiber is coated with a protective coating to protect the optical fiber from soil corrosion and mechanical damage. Multiple metal probes can be distributed and installed according to a certain layout scheme, such as the nine-square grid layout commonly used in soil and water conservation, so as to achieve comprehensive monitoring of a large area.

[0029] In the online monitoring system for soil erosion of the present invention, the monitoring optical fiber is connected to an optical frequency domain reflectometry (OFDR) demodulation module. Since OFDR has a high spatial resolution that can reach the sub-millimeter level, it can monitor the physical state changes of each point in the optical fiber in real time. The present invention can achieve high-resolution detection of strain and temperature along the length direction of the optical fiber through OFDR, and achieve precise positioning of the spatial position through signal demodulation. OFDR relies on the frequency domain interference characteristics of the optical signal injected into the optical fiber and the backscattered Rayleigh signal in the optical fiber. Through frequency modulation, interference demodulation and conversion from frequency domain to spatial domain, it can accurately sense the stress or temperature changes at any point in the optical fiber.

[0030] Specifically, OFDR works based on the Rayleigh scattering effect in optical fibers. Rayleigh scattering is caused by the inhomogeneity of the microstructure inside the optical fiber. When a laser beam is injected into an optical fiber, due to the random microscopic fluctuations in the refractive index and geometry of the optical fiber material, part of the light will be backscattered to form a Rayleigh scattering signal. The intensity and phase of the Rayleigh scattering signal reflect the microstructural characteristics inside the optical fiber. In the absence of any external disturbance on the optical fiber, the Rayleigh scattering signal has unique characteristics along the length of the optical fiber. However, when the optical fiber is subjected to external forces (such as stress or temperature), its geometry and refractive index will change slightly, causing the phase and intensity of the Rayleigh scattering signal to shift. OFDR senses the external forces acting on the optical fiber by measuring this changing signal.

[0031] like Figure 2As shown, OFDR uses a linearly modulated laser source to generate an optical signal with a continuous frequency change. When this modulated optical signal propagates into the optical fiber, Rayleigh scattering occurs at each point inside the optical fiber. The backward component in the scattered signal returns to the detector and interferes with the reference beam reflected back by the reference arm at the coupler. The interference signal contains the amplitude and phase information of the Rayleigh scattered signal. At the same time, since the frequency of the modulated optical signal changes linearly, the spectral characteristics of the interference signal have a one-to-one correspondence with the position of the scattering point in the optical fiber. In the optical frequency domain reflection demodulation unit, the relationship between the frequency of the optical signal injected into the distributed optical fiber and the length of the optical propagation path in the distributed optical fiber is as follows: (1); in, is the frequency difference, is the frequency modulation rate of the optical signal, is the change in the geometric position of the scattering point in the distributed optical fiber.

[0032] By performing Fourier transform on the spectrum of the interference signal, the frequency domain information can be converted into spatial domain information, thereby accurately locating the position of each scattering point in the optical fiber.

[0033] The OFDR used in the present invention can detect changes in optical fiber stress or temperature with high sensitivity. This sensitivity comes from the high sensitivity of Rayleigh scattering phase changes to optical fiber geometric deformation. When an optical fiber is subjected to external forces, its length will change slightly, causing the phase of the Rayleigh scattering signal to shift. The relative change in the phase change of the scattered signal and the length of the optical fiber is as follows (2): (2); in, is the phase change of the Rayleigh scattering signal, is the effective refractive index of the optical fiber, is the wavelength of the injected optical signal.

[0034] Combining the definition of strain, the relationship between distributed optical fiber strain and Rayleigh scattering phase change is obtained as follows: (3); in, is the strain of the distributed optical fiber.

[0035] It can be seen that by detecting phase changes through OFDR, the strain distribution of the optical fiber can be accurately calculated. There is usually a linear relationship between , is the elastic modulus, so OFDR can further sense the stress distribution applied to the optical fiber.

[0036] like Figure 3 As shown, since the spatial resolution of OFDR is determined by the modulation bandwidth of the laser source, the wider the modulation bandwidth, the smaller the fiber length unit that the system can resolve. The OFDR of the present invention adopts a modulation bandwidth of GHz level, which can achieve sub-millimeter spatial resolution. At the same time, the positioning accuracy of OFDR is affected by many factors, including the optical parameters of the optical fiber material, the linearity of the frequency modulation, the signal-to-noise ratio of the system, and the stability of the ambient temperature. In order to achieve high-precision positioning, the OFDR of the present invention combines coherent detection technology to improve the signal quality, and adopts a precise calibration method to eliminate errors. The high-precision positioning characteristics of OFDR enable it to perform distributed perception of the strain or temperature distribution in the optical fiber and locate the physical state changes of each scattering point. In the present invention, OFDR is used to monitor the stress distribution of the optical fiber along the length direction in real time, and locate the interface position of the soil and the air by identifying the mutation position of the stress. The stress change of the soil on the optical fiber directly reflects the state of the soil and the dynamic process of soil erosion. OFDR can accurately capture millimeter-level interface changes, quantify the amount of soil erosion, and realize early warning of soil erosion risks in combination with soil moisture change monitoring.

[0037] Furthermore, in the present invention, the position of the soil-air interface corresponds to the mutation point in the optical fiber stress distribution, and its position satisfies the extreme value condition of the stress change rate: (4); in, is the stress change rate, is stress, is the position variable of the soil-air interface, is the position of the soil-air interface, is the set interface mutation judgment threshold.

[0038] Through continuous monitoring The change in the depth of soil erosion can be quantitatively evaluated. , and then calculate the amount of soil and water loss.

[0039] Furthermore, the data processing unit of the present invention has a humidity distribution measurement module, which can calculate the humidity distribution and humidity gradient of the soil to be tested based on the stress distribution data monitored by the distributed optical fiber and the soil humidity relationship model. In addition to the direct monitoring of the amount of soil erosion, the present invention also infers the distribution and gradient of humidity along the depth through the relationship between stress and soil humidity.

[0040] Since soil moisture has a significant effect on the bonding force between soil particles, the greater the moisture, the looser the soil, and the smaller the force on the probe. Through experimental calibration, a relationship model between soil moisture and stress is established: (5); in, is the moisture distribution of the soil to be tested, is the stress in dry soil state, is the soil moisture distribution, is the humidity influencing factor.

[0041] The moisture gradient of the soil to be tested is expressed as the following formula (6): (6); in, is the moisture gradient of the soil to be tested, For external stress.

[0042] Humidity gradient is an important assessment indicator of soil erosion risk. When the soil moisture gradient exceeds the preset threshold, the humidity distribution measurement module can generate a soil erosion risk warning signal based on the following formula (7): (7); in, is a risk factor, and is an empirical coefficient related to soil type and environmental conditions, is the humidity gradient; when >Risk Threshold R th When the humidity distribution measurement module triggers the soil and water loss risk warning signal.

[0043] The present invention also discloses an online monitoring method for soil and water loss based on optical frequency domain reflection, comprising the following steps: First, insert the metal probe into the soil in the monitoring area, and adjust the burial depth and layout density. Then, collect the optical fiber stress distribution data through the optical frequency domain reflectometer, and analyze the dynamic position of the soil-air interface in real time. Next, calculate the amount of soil and water loss based on the stress distribution data, and infer the soil moisture and its gradient based on the humidity distribution model. Finally, evaluate the potential risk of soil and water loss through humidity gradient and risk factors, and generate early warning signals according to preset thresholds.

[0044] The present invention utilizes the high-resolution characteristics of OFDR technology to achieve millimeter-level spatial resolution and high-sensitivity stress monitoring, and can grasp the dynamic changes of soil erosion in real time; at the same time, combined with humidity distribution and gradient analysis, it predicts the potential risk of soil erosion and provides early warning. The system can be widely used in the fields of soil and water conservation, agricultural irrigation management, ecological disaster early warning, etc., providing technical support for land resource management and ecological environment protection.

[0045] The present invention is further described in detail below through specific examples.

[0046] The buried depth of the measuring rod of the present invention can be adjusted according to the soil type and monitoring requirements. A plurality of metal measuring rods are arranged in the monitoring area to form a monitoring network, and wide-area monitoring is achieved through distributed perception of the entire area.

[0047] The OFDR in the present invention is composed of a frequency modulated laser source, an interference coupler, a photodetector and a signal processing unit. The laser light source outputs a linearly modulated optical signal and injects it into the optical fiber. Rayleigh scattering occurs inside the optical fiber due to the microscopic inhomogeneity of the material, where the back Rayleigh scattered signal returns to the OFDR module and interferes with the reference beam in the coupler. The interference signal contains information about the internal state change of the optical fiber, which is converted into an electrical signal by a photodetector and analyzed. OFDR converts the frequency domain characteristics of the interference signal into spatial domain information through Fourier transform, thereby realizing the precise positioning of any position in the optical fiber and the distributed perception of strain changes.

[0048] In actual use, metal probes are first arranged in a predetermined grid in the monitoring area, such as a nine-square grid, to ensure full coverage of the target area. Each probe is connected to the OFDR to form a continuous monitoring link. The Rayleigh scattering signal of the optical fiber along the length direction is obtained in real time by OFDR, and the stress distribution of the optical fiber is obtained by demodulating the signal. The mutation point of stress corresponds to the position of the soil-air interface. By analyzing the changes in the mutation point, the amount of soil and water loss can be determined.

[0049] In order to improve the monitoring accuracy, the present invention further analyzes the change of humidity distribution and gradient by establishing a stress-soil humidity relationship model. Humidity has a significant effect on the cohesion of soil particles. The higher the humidity, the smaller the force of the soil on the measuring rod. By experimentally calibrating the stress changes under different humidity conditions, the humidity influence factor is obtained. and dry soil base stress Based on the soil moisture relationship model, the distribution function of soil moisture can be inferred by solving the fiber stress distribution. At the same time, the risk of soil erosion in local areas can be identified through humidity gradient calculation.

[0050] Based on the above, in the experimental verification of the present invention, the system was deployed in a slope erosion area, the optical fiber spatial resolution was set to 500 microns, and the monitoring period was 10 minutes. The experimental results show that the present invention can capture millimeter-level soil interface changes, quantify soil and water loss, and accurately evaluate high-risk areas through dynamic changes in humidity gradients and distributions. By combining direct monitoring of soil and water loss with the indirect impact of humidity changes, accurate management of soil and water conservation and disaster warning are achieved.

[0051] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the specification and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. An online monitoring system for soil and water loss based on optical frequency domain reflection, characterized in that: It includes an optical fiber detection unit, an optical frequency domain reflection demodulation unit and a data processing unit, wherein: The optical fiber detection unit includes an optical fiber detection part, which includes a measuring rod and a distributed optical fiber located on the outer wall of the measuring rod, and the outer side of the distributed optical fiber has a protective layer; at least a part of the optical fiber detection unit can be placed in the soil to be tested so as to measure the soil to be tested; The optical frequency domain reflection demodulation unit is connected to the distributed optical fiber; the optical frequency domain reflection demodulation unit is used to obtain the Rayleigh scattering signal in the distributed optical fiber, and obtain the stress distribution data of the distributed optical fiber through frequency domain demodulation; The data processing unit is used to determine the position of the interface stress mutation between the soil to be tested and the air according to the stress distribution data, and calculate the amount of soil and water loss of the soil to be tested by the change of the interface stress mutation position; The data processing unit is also used to calculate the moisture distribution and moisture gradient of the soil to be tested, generate real-time warning signals based on the moisture distribution and moisture gradient, and evaluate the soil erosion risk of the soil to be tested.

2. The online monitoring system for soil and water loss based on optical frequency domain reflectometry according to claim 1 is characterized in that: In the optical frequency domain reflection demodulation unit, the relationship between the frequency of the optical signal injected into the distributed optical fiber and the length of the optical propagation path in the distributed optical fiber is as follows: （1）； in, is the frequency difference, is the frequency modulation rate of the optical signal, is the geometric position change of the scattering point in the distributed optical fiber; The relative change of the phase change of the scattered signal and the fiber length is as follows (2): (2)； in, is the phase change of the Rayleigh scattering signal, is the effective refractive index of the optical fiber, is the wavelength of the injected optical signal. Combined with the definition of strain, the relationship between the distributed optical fiber strain and the Rayleigh scattering phase change is obtained as follows: (3)； in, is the strain of the distributed optical fiber; The phase change is detected by optical frequency domain reflection and the strain distribution of the optical fiber is calculated.

3. The online soil and water loss monitoring system based on optical frequency domain reflectometry according to claim 1 is characterized in that: The data processing unit determines the position of the sudden change in the interface stress between the soil and the air, and calculates the amount of soil and water loss of the tested soil by the change in the position of the sudden change in the interface stress. Specifically, it includes: The position of the soil-air interface corresponds to the mutation point in the optical fiber stress distribution, and its position satisfies the extreme value condition of the stress change rate: （4）； in, is the stress change rate, is stress, is the position variable of the soil-air interface, is the position of the soil-air interface, is the set interface mutation judgment threshold.

4. The online soil and water loss monitoring system based on optical frequency domain reflectometry according to claim 1 is characterized in that: The data processing unit is provided with a humidity distribution measurement module, which can calculate the humidity distribution and humidity gradient of the soil to be tested based on the stress distribution data monitored by the distributed optical fiber and in combination with the soil humidity relationship model.

5. The online monitoring system for soil and water loss based on optical frequency domain reflection according to claim 4 is characterized in that: The soil moisture relationship model adopts the following formula (5): （5）； in, is the moisture distribution of the soil to be tested, is the stress in dry soil state, is the soil moisture distribution, is the humidity influencing factor.

6. The online monitoring system for soil and water loss based on optical frequency domain reflection according to claim 4 is characterized in that: The moisture gradient of the soil to be tested is expressed as the following formula (6): （6）； in, is the moisture gradient of the soil to be tested, For external stress.

7. The online soil and water loss monitoring system based on optical frequency domain reflectometry according to claim 4 is characterized in that: When the soil moisture gradient exceeds the preset threshold, the humidity distribution measurement module can generate a soil erosion risk warning signal based on the following formula (7): （7）； in, is a risk factor, and is an empirical coefficient related to soil type and environmental conditions, is the humidity gradient; when >Risk Threshold R th When the humidity distribution measurement module triggers the soil and water loss risk warning signal.

8. The online soil and water loss monitoring system based on optical frequency domain reflectometry according to claim 1 is characterized in that: A plurality of optical fiber detectors are provided, and the burial depths of the plurality of optical fiber detectors are adjusted and confirmed according to the soil type and monitoring requirements. The plurality of optical fiber detectors are inserted according to preset positions in the monitoring area so as to form a monitoring network.

9. The online soil and water loss monitoring system based on optical frequency domain reflectometry according to claim 1 is characterized in that: The distributed optical fiber is embedded and fixed to the outer wall of the probe, and the protective layer includes a polymer protective coating located on the distributed optical fiber.

10. An online monitoring method for soil and water loss based on optical frequency domain reflection, characterized in that: The method is based on the online soil and water loss monitoring system based on optical frequency domain reflection according to any one of claims 1 to 9, and comprises the following steps: S1. Insert the optical fiber detector into the soil of the monitoring area and adjust the burial depth and layout density; S2, the optical frequency domain reflection demodulation unit collects the Rayleigh scattering signal in the distributed optical fiber, performs frequency domain demodulation, and obtains the stress distribution data of the optical fiber along the length direction; S3. The data processing unit analyzes the stress distribution data, identifies the location of stress mutation, determines the dynamic position of the interface between the tested soil and the air, calculates the amount of soil erosion, calculates the moisture distribution and moisture gradient of the tested soil, evaluates the potential risk of soil erosion, and generates a warning signal according to a preset threshold.

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