Irrigation area soil salt deposit property exploration method based on cooperation of unmanned aerial vehicle and ground penetrating radar

Abstract

The invention discloses an irrigated area soil salt deposit property exploration method based on cooperation of an unmanned aerial vehicle and a ground penetrating radar, and relates to the field of metrology soil science, and the method comprises the steps: inputting the surface temperature data of a target field into a seasonal frozen soil area soil freezing depth prediction model, outputting the soil freezing depth, and determining a freezing depth change curve; according to the freezing depth change curve, the maximum freezing depth period of the soil in the irrigation area is selected as the optimal exploration time of the ground penetrating radar GPR, and GPR related parameters are determined in combination with the average depth of the local salt deposit layer where the target field parcel is located; the unmanned aerial vehicle is used for conducting topographic survey on the target field within the GPR optimal survey time, and a GPR wiring scheme is determined according to topographic data; on the basis of the wiring scheme and the parameters, performing salt deposit layer character exploration on the target field parcel by using a GPR, and constructing a visual model; the visual model is used for displaying the properties of the salt deposit layer; the properties of the salinized layer comprise the burial depth of the salinized layer and the salt content of the salinized layer. According to the method, the properties of the salinized layer can be accurately analyzed and quantitatively represented.

Description

Technical Field

[0001] The present application relates to the field of quantitative soil science, and in particular to a method for surveying the properties of salt accumulation layers in irrigated areas based on the collaboration of unmanned aerial vehicles and ground penetrating radar. Background Art

[0002] The salt layer refers to a salt-rich area formed by the gradual accumulation of soluble salts in the shallow soil layer due to the combined effects of groundwater evaporation and winter irrigation salt pressure. The existence of the salt layer will not only significantly change the physical and chemical environment of the crop root zone, inhibit crop growth and reduce yields, but may also cause secondary problems such as soil structure degradation and deterioration of tillage performance. In severe cases, it may even lead to land desertification. Due to the strong variability of the salt layer, accurately grasping the high-precision spatial distribution characteristics, thickness and salt content of the salt layer is of great significance for characterizing the regional soil hydrological balance, formulating scientific salt regulation strategies and implementing soil improvement measures. At present, the detection of salt layers mainly relies on traditional drilling survey methods. Although this method can directly obtain soil samples, it has the limitations of low efficiency, strong destructiveness and high uncertainty in practical applications. In the practice of salinized soil control and saline-alkali land improvement, traditional drilling methods often fail to meet the needs of fine characterization of the spatial distribution characteristics of salt layer properties.

[0003] In recent years, with the continuous advancement of geophysical exploration technology, ground-penetrating radar (GPR) technology has gradually been introduced into the field of soil structure detection due to its non-invasive, high efficiency and real-time continuous imaging. Compared with traditional methods, GPR has the technical advantages of high efficiency, non-destructiveness and simple operation, providing a new technical means for soil layer survey. Existing GPR surveys are usually carried out under conventional conditions. However, the high salt content of the soil in the irrigation area will cause strong energy attenuation of the electromagnetic wave during the propagation process, making it difficult for the reflected signal to be effectively captured by the detection system, which seriously restricts the ability of GPR to survey the structure of the salt layer in the irrigation area. As a result, it is often difficult to obtain sufficiently clear and high signal-to-noise ratio reflected signals in GPR surveys under normal temperature conditions, thus affecting the accurate analysis and quantitative characterization of the properties of the salt layer. Summary of the invention

[0004] The purpose of this application is to provide a method for surveying the properties of salt layers in irrigated areas based on the collaboration of UAVs and ground penetrating radars, so as to solve the problem that the existing GPR survey cannot obtain salt layer signals and thus cannot analyze and quantitatively characterize the properties of salt layers.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a method for surveying the properties of salt accumulation layers in irrigated soil, comprising:

[0007] The surface temperature data, average soil moisture content and soil bulk density of the target field are input into the soil freezing depth prediction model in seasonal frozen soil areas, and the freezing depth change curve is output;

[0008] According to the freezing depth variation curve, the maximum freezing depth period of the irrigated soil is selected as the GPR optimal survey time of the GPR, and the GPR parameters are determined in combination with the average depth of the salt accumulation layer in the target field area;

[0009] Using drones to conduct topographic surveys of target fields within the GPR optimal survey time, and determining GPR wiring plans based on topographic data;

[0010] Based on the GPR parameters and wiring scheme, the GPR is used to survey the properties of the salt layer on the target field to determine a visualization model; the visualization model is used to display the properties of the salt layer; the properties of the salt layer include the burial depth of the salt layer and the salt content of the salt layer.

[0011] According to the specific embodiments provided in the present application, the present application discloses the following technical effects: when soil is frozen, the salt content and apparent dielectric constant of the soil body will be significantly reduced, thereby weakening the energy attenuation during the propagation of electromagnetic waves, enabling them to propagate farther distances and obtain stronger reflection signals. In the soil distribution area of ​​the irrigation area, seasonal freezing is common. Based on this, the present invention innovatively utilizes the special physical conditions during soil freezing, and optimizes the survey timing and parameter configuration of the ground penetrating radar to achieve non-invasive detection of salt layers below the freezing depth.

[0012] Specifically, we first collect surface temperature data and determine the freezing depth change curve based on the freezing depth prediction model to ensure that the detection work is carried out under the best freezing conditions, so as to accurately determine the depth and salt content of the salt layer. We use the freezing period for detection to overcome the attenuation of electromagnetic waves, avoiding the problem of GPR surveys under normal temperature conditions that are difficult to obtain sufficiently clear reflection signals with a high signal-to-noise ratio, thereby enabling accurate analysis and quantitative characterization of the properties of the salt layer.

[0013] In addition, this application combines terrain data obtained by drones to determine the GPR wiring plan, providing comprehensive, intuitive and scientific data support for water and salt regulation and soil improvement in local saline-alkali land. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 Flow chart of the method for surveying the properties of the salt layer in the irrigated area soil provided for this application;

[0016] Figure 2 A schematic diagram of the relative elevation of the ground surface corresponding to the target field provided for this application;

[0017] Figure 3 An example diagram of the reflection signal of the salt layer obtained by the ground penetrating radar provided in this application under freezing conditions;

[0018] Figure 4 Schematic diagram of the visualization model provided for this application. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0021] The embodiment of the present application provides a method for surveying the properties of salt accumulation layers in irrigated areas. The method uses the cooperation of drones and ground-penetrating radars to accurately survey the properties of salt accumulation layers in irrigated areas. The method uses the seasonal soil freezing conditions in irrigated areas to conduct ground-penetrating radar detection, which overcomes the difficulty that the electromagnetic waves of ground-penetrating radars cannot identify the salt accumulation layers in salinized farmland soils due to rapid attenuation under conventional non-freezing conditions. The method also combines drilling information to accurately obtain the buried depth (i.e., burial depth) and salt content of the salt accumulation layer. The method is executed by a computer device, which can be executed by a computer device such as a terminal or a server alone, or by a terminal and a server together. In the embodiment of the present application, Figure 1 As shown, the method includes the following steps.

[0022] S1: Input the surface temperature data, average soil moisture content and soil bulk density of the target field into the soil freezing depth prediction model in seasonal frozen soil areas, and output the freezing depth change curve.

[0023] S2: According to the freezing depth variation curve, the maximum freezing depth period of the soil in the irrigation area is selected as the GPR optimal survey time of the GPR, and the GPR parameters are determined in combination with the average depth of the salt accumulation layer in the area where the target field is located.

[0024] The optimal GPR survey time should meet the following requirements: the freezing depth reaches a relatively deep level and is not too close to the average depth of the local salt layer, which is the salt layer in the area where the target field is located.

[0025] S3: Use the UAV to conduct terrain survey on the target field within the GPR optimal survey time, and determine the GPR wiring plan based on the terrain data.

[0026] S4: Based on the GPR parameters and wiring scheme, the GPR is used to survey the properties of the salt layer on the target field to determine a visualization model; the visualization model is used to display the properties of the salt layer; the properties of the salt layer include the burial depth of the salt layer and the salt content of the salt layer.

[0027] In an exemplary embodiment, before S1, the step further includes: constructing a soil freezing depth prediction model in a seasonal frozen soil area; the specific implementation steps of the soil freezing depth prediction model in a seasonal frozen soil area are as follows:

[0028] S11: Calculate the freezing index (F) cumulatively through real-time monitoring of the daily average temperature data.

[0029] F=∑|T i |

[0030] Where T i The average daily temperature is below zero degrees.

[0031] S12: Establish soil parameter model and calculate soil volume latent heat (Q) using water freezing latent heat (L), average soil moisture content (θ) and soil bulk density (ρ). L ).

[0032] Q L =Lθρ

[0033] S13: Calculate the freezing depth (d) by calculating the soil thermal conductivity using the freezing index, soil volume latent heat and soil thermal conductivity (k) f ), the specific relationship is as follows:

[0034]

[0035] In an exemplary embodiment, S2 selects appropriate GPR parameters according to the average depth of the salt layer, and the GPR parameters include a center frequency and a time window.

[0036] In an exemplary embodiment, S3 may be replaced by the following steps.

[0037] S31: Using a drone to conduct a terrain survey on the target field within the GPR optimal survey time to generate a digital elevation model.

[0038] S32: Determine the target field terrain data according to the digital elevation model.

[0039] S33: Based on the terrain data, the direction with the largest change in overall surface slope is selected as the GPR wiring measurement direction, and a plurality of parallel GPR survey lines are set to cover the target field, thereby generating a GPR wiring plan.

[0040] In an exemplary embodiment, S4 may be replaced by the following steps.

[0041] S41: Select a drilling location in the GPR wiring scheme, collect soil profile samples, and use the GPR parameters to obtain a salt layer reflection signal at the drilling location.

[0042] In practical applications, 3 to 5 representative drilling locations are set in a typical GPR survey line in a GPR wiring plan.

[0043] In practical applications, soil profile samples are collected at selected borehole locations and tested for salt content.

[0044] S42: Determine the buried depth of the salt layer of each GPR survey line in the GPR wiring scheme according to the salt layer reflection signal.

[0045] S43: Fitting the salt content of the salt layer of the soil profile sample and the burial depth of the salt layer corresponding to the drilling position to generate a relationship between the burial depth of the salt layer and the salt content.

[0046] S44: Determine the salt content of the salt layer at all measurement positions on all GPR survey lines according to the relationship between the buried depth of the salt layer and the salt content and the buried depth of the salt layer of each GPR survey line.

[0047] S45: Determine a visualization model based on the buried depth of the salt layer of each GPR survey line and the salt content of the salt layer at all measurement locations.

[0048] In an exemplary embodiment, S42 may be replaced by the following steps.

[0049] S421: Based on the common offset method, a first GPR signal is collected, and a first salt layer reflection signal and a propagation time corresponding to the first GPR signal are extracted.

[0050] S422: Based on the wide-angle reflection-refraction method fitting model, a second GPR signal is collected, a second salt accumulation layer reflection signal corresponding to the second GPR signal is extracted, and an average wave velocity is fitted according to the second salt accumulation layer reflection signal.

[0051] S423: Calculate the buried depth of the salt layer of each GPR survey line in the GPR wiring scheme according to the average wave velocity and the propagation time corresponding to the reflection signal of the first salt layer.

[0052] In practical applications, the common offset method is used to collect the first GPR signal along the determined GPR survey line to obtain the propagation time corresponding to the reflection signal of the first salt layer. At the same time, wide-angle reflection and refraction method tests are carried out at both ends of each GPR survey line to fit the average wave velocity, and the buried depth of the salt layer is calculated based on the signal propagation time.

[0053] In practical applications, the collected GPR signals (i.e., the original GPR time domain signals) are subjected to low-frequency noise reduction processing to extract the precise reflection signal and propagation time of the salt layer. The wide-angle reflection and refraction method is used to obtain the electromagnetic wave propagation velocity of the target field, and the burial depth of the salt layer is calculated by combining the propagation time of the reflection signal with the electromagnetic wave propagation velocity.

[0054] In an exemplary embodiment, S423 may be replaced by the following steps.

[0055] The propagation time of the first salt layer reflection signal corresponding to the first GPR signal measured by the common offset method is combined with Calculate the burial depth of the salt layer; where d is the burial depth of the salt layer; t CO is the reflection time of the salt layer reflection signal obtained by the common offset method; v is the average wave velocity. The average wave velocity is obtained by fitting the model of the wide-angle reflection and refraction method, and the model is expressed as The different antenna spacings (x i ) and the corresponding wide-angle reflection-refraction method salt layer reflection signal propagation time (t i ) is the fitting variable; the theoretical propagation time of the reflected signal from the salt layer when the antenna spacing is zero (t 0 ) and average velocity (v) are fitting parameters.

[0056] In an exemplary embodiment, S45 may be replaced by the following steps.

[0057] The depth and salt content of the salt layer are spatially reconstructed by using smoothing filtering and three-dimensional linear interpolation methods to determine the reconstructed model; the reconstructed model only shows the depth of the salt layer.

[0058] The salt content of the salt layer is superimposed on the reconstructed model as a soil attribute layer through three-dimensional relief technology, generating a visualization model that simultaneously displays the burial depth and salt content of the salt layer.

[0059] Take the salt layer survey of a certain field (30m×38m) as an example:

[0060] Step 1: Prediction of freezing depth, determination of ground-penetrating GPR parameters and determination of survey time: By collecting data, it is known that the thickness of the salt layer in the target field is about 1.0m. After collecting the parameters of the target field, it is calculated that the freezing depth of the target field in mid-January is 0.55-0.65m, so the survey date is determined to be mid-January. According to the burial depth of the salt layer and the best survey time, the test selected a 400MHz GPR antenna, a survey time window of 50ns, and a sampling interval of 0.025m.

[0061] Step 2: Surface elevation acquisition, GPR survey wiring design and borehole sampling: Use drones to conduct high-precision terrain surveys of target fields and generate digital elevation models, such as Figure 2 As shown. It was found that the overall slope of the target field was toward the north, so the north-south direction was selected as the GPR survey line setting direction. A total of 20 parallel survey lines were set up in the experiment, with a survey line spacing of 2m. Further, three drilling points were selected on the sixth typical survey line, located at 6m, 17m, and 24m of the survey line, and the salt content of the salt layer was obtained by indoor measurement.

[0062] Step 3: GPR data collection: GPR signals are collected along the preset survey line in step 2 using the common offset method, such as Figure 3 As shown, a wide-angle reflection-refraction method test is set up at both ends of the measuring line.

[0063] Step 4: Signal preprocessing and calculation of salt layer burial depth: After noise reduction processing of the original GPR signal, the average electromagnetic wave propagation velocity of the target field is obtained by fitting the wide-angle reflection and refraction method data, which is 0.115m / ns. The propagation time of the salt layer reflection signal is extracted from the common offset method data, and the salt layer burial depth is calculated in combination with the electromagnetic wave propagation velocity.

[0064] Step five, obtaining the salt content of the salt layer based on data fusion: using the soil salt content obtained in step four as the characteristic vector of the three-dimensional distribution of the salt layer, and the burial depth data of the salt layer at the corresponding position as the corresponding feature in the salt layer data set for data fusion, generalizing the salt content of the salt layer with a linear relationship, and using this correlation to obtain the salt content of the salt layer in the target field with the same data structure as the burial depth of the salt layer.

[0065] Step 6: 3D construction of salt layer: Use smoothing filtering and 3D linear interpolation methods to reconstruct the burial depth space of the salt layer. Finally, the salt content information of the salt layer is superimposed on the burial depth of the 3D salt layer as a soil attribute layer through 3D relief technology to form a 3D salt layer shape visualization model, such as Figure 4 shown.

[0066] This application innovatively uses seasonal soil freezing conditions in irrigation areas for ground penetrating radar detection, breaking through the difficulty that GPR electromagnetic waves cannot identify salt accumulation layers in salinized farmland soil due to rapid attenuation under conventional non-freezing conditions. The soil salt layer properties and drilling information are superimposed on the surface elevation data obtained by drones through three-dimensional relief technology, thereby achieving accurate acquisition and comprehensive display of spatial distribution information on the burial depth and salt content of the salt layer.

[0067] Specifically include: Step A, freezing depth estimation and survey timing determination: According to the surface temperature data of the target field and the soil freezing depth prediction model in the seasonal frozen soil area, the soil freezing depth is estimated and a suitable date is selected as the survey timing.

[0068] Step B, surface elevation acquisition, GPR survey wiring design and drilling planning: Use drones to obtain high-precision digital elevation models, set the ground-penetrating GPR wiring direction to the surface slope direction, and select 3 to 5 representative boreholes on the survey line.

[0069] Step C, ground penetrating GPR parameter setting and data acquisition: select the appropriate center frequency and time window for the ground penetrating radar, use the common offset method to collect the salt layer reflection signal along the survey line, and perform wide-angle reflection and refraction method tests at both ends of the survey line. Furthermore, collect borehole samples at the selected locations in step B.

[0070] Step D, signal processing, calculation of salt layer burial depth and indoor testing of borehole samples: noise reduction processing of the original salt layer reflection signal, and the wide-angle reflection refraction method in step C is used to test the signal propagation speed. The data obtained by the common offset method is subjected to Hilbert transform to obtain the envelope, and the propagation time corresponding to the peak of the salt layer reflection signal envelope is extracted, and the depth is calculated by the salt layer signal propagation time. At the same time, the salt content of the borehole profile sample obtained in step C is tested in the laboratory.

[0071] Step E, obtaining salt content data of the salt layer based on data fusion: using the soil salt content data obtained in step D as the characteristic vector of the three-dimensional distribution of the salt layer, and the burial depth data of the salt layer at the corresponding position as the corresponding feature in the salt layer data set for data fusion, generalizing the salt content data of the salt layer with a linear relationship, and using this correlation relationship to obtain the salt content data of the salt layer in the target field with the same structure as the burial depth data of the salt layer.

[0072] Step F, three-dimensional construction of salt layer: spatially reconstruct the burial depth and salt content data of the salt layer using smoothing filtering and three-dimensional linear interpolation methods. Furthermore, the salt content of the salt layer is superimposed as a soil attribute layer on the burial depth information of the salt layer using three-dimensional relief technology.

[0073] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for surveying the properties of salt layers in irrigated soil, characterized in that: The method for surveying the properties of the salt layer in the irrigation area soil comprises: The surface temperature data, average soil moisture content and soil bulk density of the target field are input into the soil freezing depth prediction model in seasonal frozen soil areas, and the freezing depth change curve is output; According to the freezing depth variation curve, the maximum freezing depth period of the irrigated soil is selected as the GPR optimal survey time of the GPR, and the GPR parameters are determined in combination with the average depth of the salt accumulation layer in the target field area; Using drones to conduct topographic surveys of target fields within the GPR optimal survey time, and determining GPR wiring plans based on topographic data; Based on the GPR parameters and wiring scheme, the GPR is used to survey the properties of the salt layer on the target field to determine a visualization model; the visualization model is used to display the properties of the salt layer; the properties of the salt layer include the burial depth of the salt layer and the salt content of the salt layer.

2. The method for surveying the properties of the salt layer in the irrigated area soil according to claim 1 is characterized in that: The surface temperature data, average soil moisture content and soil bulk density of the target field are input into the soil freezing depth prediction model in seasonal frozen soil areas, and the freezing depth change curve is output, including: Real-time monitoring of daily average temperature data, cumulative calculation of freezing index F, combined with soil volume latent heat Q L , using the soil freezing depth prediction model in seasonal frozen soil areas, calculate the freezing depth curve d f ; Where F = ∑|T i |, T i is the surface temperature data, which is the daily average temperature below zero degrees; Q L =L·θ·ρ, L is the latent heat of freezing of water, θ is the average soil water content, and ρ is the soil bulk density; k is the thermal conductivity of soil; A freezing depth variation curve is determined according to the soil freezing depth.

3. The method for surveying the properties of salt layers in irrigated areas according to claim 1, characterized in that: Use drones to conduct terrain surveys on target fields within the optimal GPR survey time, and determine the GPR wiring plan based on the terrain data, including: Using drones to conduct topographic surveys of target fields within the GPR optimal survey time to generate digital elevation models; determining terrain data according to the digital elevation model; Based on the terrain data, the direction with the largest change in overall surface slope is selected as the GPR survey line measurement direction, and multiple parallel GPR survey lines are set to cover the target field to generate a GPR wiring plan.

4. The method for surveying the properties of salt accumulation layers in irrigation areas according to claim 1, characterized in that: Based on the GPR parameters and wiring scheme, the GPR is used to survey the properties of the salt layer on the target field and determine the visualization model, which specifically includes: Selecting a drilling location in the GPR wiring scheme, collecting soil profile samples, and obtaining a salt layer reflection signal at the drilling location using the GPR parameters; Determine the buried depth of the salt accumulation layer of each GPR survey line in the GPR wiring scheme according to the reflection signal of the salt accumulation layer; Fitting the salt content of the salt layer of the soil profile sample and the burial depth of the salt layer corresponding to the drilling position to generate a salt layer burial depth-salt content relationship model; Determine the salt content of the salt layer at all measurement locations on all GPR survey lines according to the salt layer burial depth-salt content relationship model and the salt layer burial depth of each GPR survey line; A visualization model is constructed based on the burial depth of the salt layer of each GPR survey line and the salt content of the salt layer at all measurement locations.

5. The method for surveying the properties of salt layers in irrigated soil according to claim 4 is characterized in that: Determining the buried depth of the salt accumulation layer of each GPR survey line in the GPR wiring scheme according to the salt accumulation layer reflection signal specifically includes: Based on the common offset method, a first GPR signal is collected, and a first salt accumulation layer reflection signal and a propagation time corresponding to the first GPR signal are extracted; Based on the wide-angle reflection-refraction method fitting model, a second GPR signal is collected, a second salt accumulation layer reflection signal corresponding to the second GPR signal is extracted, and an average wave velocity is fitted according to the second salt accumulation layer reflection signal; The buried depth of the salt accumulation layer of each GPR survey line in the GPR wiring scheme is calculated according to the average wave velocity and the propagation time corresponding to the reflection signal of the first salt accumulation layer.

6. The method for surveying the properties of salt layers in irrigated soil according to claim 5, characterized in that: According to the average wave velocity and the propagation time corresponding to the reflection signal of the first salt accumulation layer, the buried depth of the salt accumulation layer of each GPR survey line in the GPR wiring scheme is calculated, specifically including: According to the propagation time of the reflected signal of the first salt accumulation layer, combined with Calculate the depth of the salt layer buried in each GPR survey line in the GPR wiring scheme; where d is the depth of the salt layer buried; t CO is the propagation time of the reflection signal of the first salt accumulation layer; v is the average wave velocity, which is obtained by fitting the model of the wide-angle reflection and refraction method. The fitting model of the wide-angle reflection and refraction method is Among them, different antenna spacing x i and the corresponding propagation time t of the reflected signal from the salt layer i are fitting variables; when the antenna spacing is zero, the theoretical propagation time (t0) and average velocity (v) of the reflected signal from the salt layer are fitting parameters.

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