A method and device for measuring soil physical and chemical properties for desert steppe restoration

Abstract

The present application relates to the technical field of soil monitoring, in particular to a method and device for measuring soil physical and chemical properties for desert steppe restoration. The method comprises: obtaining the vegetation coverage, salt content index and temperature of the soil at the sampling points in different geographical locations in the desert steppe restoration area; determining the true dielectric constant based on the mass change of the soil before and after drying; obtaining the apparent dielectric constant at different oscillation frequencies; determining the optimal measurement frequency by combining the difference between the apparent dielectric constant and the true dielectric constant; determining the salt consistency coefficient according to the geographical location difference, vegetation coverage difference and salt content index difference between the current point and other sampling points; selecting similar points to determine the target frequency of the current point at the real-time temperature; performing FDR measurement based on the target frequency to obtain the current dielectric constant, and determining the water content based on the current dielectric constant. The present application can improve the accuracy of water content analysis.

Description

Technical Field

[0001] This invention relates to the field of soil monitoring technology, specifically to a method and apparatus for determining the physicochemical properties of soil used in desert steppe restoration. Background Technology

[0002] Most existing methods for determining soil moisture content involve accurately measuring the apparent dielectric constant of the soil and then calculating the moisture content using empirical formulas (such as the Topp formula). Since the dielectric constant is typically expressed as a complex number, with its real part representing the soil's ability to store electromagnetic energy and its imaginary part representing its ability to dissipate electromagnetic energy, traditional calculations using empirical formulas often neglect the imaginary part of the dielectric constant, using only the real part. However, in reality, desertified grassland soils have high salinity, and the imaginary part of the dielectric constant usually cannot be ignored. Furthermore, the large diurnal temperature range in desertified grasslands means that temperature has a very strong effect on the imaginary part, which also cannot be simply ignored.

[0003] When using existing sensors based on frequency domain reflection / capacitance method (FDR) to determine the dielectric constant, the actual effect of salt on the dielectric constant and the performance of different salt concentrations at different temperatures are not measured. Only the effect of temperature on the dielectric constant at standard salt concentrations is considered, and the optimal active detection oscillation frequency cannot be determined. This usually results in errors in the dielectric constant reading, ultimately leading to low accuracy in the calculated moisture content. Summary of the Invention

[0004] To address the technical problem of low accuracy in calculating moisture content in related technologies, this invention provides a method and apparatus for determining the physicochemical properties of soil for desert steppe restoration. The specific technical solution adopted is as follows:

[0005] This invention proposes a method for determining the physicochemical properties of soil used in desert steppe restoration, the method comprising:

[0006] To obtain soil samples from different geographical locations in the desert steppe restoration area, including vegetation cover, salinity, and temperature.

[0007] Under a fixed temperature at the sampling point, the true dielectric constant is determined based on the change in soil mass before and after drying; the apparent dielectric constant of the soil at different oscillation frequencies is obtained by adjusting the FDR oscillation frequency; the optimal measurement frequency is determined by combining the difference between the apparent dielectric constant and the true dielectric constant; and the optimal measurement frequency at different temperatures at the sampling point is obtained.

[0008] Based on the differences in geographical location and vegetation coverage between the current point and other sampling points, the similarity of salt ion types is determined; combining the similarity of salt ion types and the differences in salt content indicators, the salt consistency coefficient between the current point and other sampling points is determined; similar points are selected from other sampling points based on the salt consistency coefficient; and the target frequency of the current point at the real-time temperature is determined by combining the optimal measurement frequencies of all similar points at different temperatures.

[0009] FDR measurement is performed based on the target frequency to obtain the current dielectric constant, and the water content is determined based on the current dielectric constant.

[0010] Furthermore, determining the true dielectric constant based on the change in soil mass before and after drying includes:

[0011] The soil at the same sampling point was divided into different sampling groups. Soil drying was performed on each sampling group. The true moisture content was determined based on the change in soil quality before and after drying.

[0012] Based on the Topp formula, the true moisture content is converted into the true dielectric constant.

[0013] Furthermore, the adjustment of the FDR oscillation frequency to obtain the apparent dielectric constant of the soil at different oscillation frequencies includes:

[0014] The oscillation frequencies are selected according to the preset step size to obtain the measurement frequencies; based on the measurement frequencies, the resonant frequencies of each measurement frequency are obtained by using FDR detection.

[0015] Based on the resonant frequency and the dielectric constant calculation formula used during instrument factory calibration, the apparent dielectric constant is calculated.

[0016] Furthermore, determining the optimal measurement frequency by combining the difference between the apparent dielectric constant and the true dielectric constant includes:

[0017] The difference between the true dielectric constant and the apparent dielectric constant at different measurement frequencies is calculated to obtain the dielectric difference index.

[0018] A two-dimensional rectangular coordinate system is constructed with the dielectric difference index as the vertical axis and the measurement frequency as the horizontal axis. The coordinate points corresponding to the dielectric difference index at different measurement frequencies in the coordinate system are determined.

[0019] Curve fitting is performed on all coordinate points using the multi-term least squares fitting method, and the fitting is extended until the extended curve intersects the axis with a vertical coordinate of 0. The measurement frequency under the intersection condition is taken as the optimal measurement frequency.

[0020] Furthermore, the geographical location includes the elevation data of the current point and other sampling points, as well as the elevation data of the surrounding terrain. The determination of salt ion similarity based on the geographical location differences and vegetation cover differences between the current point and other sampling points includes:

[0021] Based on the topographic elevation map of the desert grassland restoration area obtained from the geographic information system, the topographic coordinates of the current point and other sampling points on the topographic elevation map are determined.

[0022] Determine the terrain similarity between the current point and other sampling points based on the terrain coordinates and the surrounding terrain distribution;

[0023] The absolute value of the difference in vegetation coverage between the current point and other sampling points is calculated as the coverage difference, and the absolute value of the difference in terrain height is calculated as the terrain difference.

[0024] The similarity of salt ion species was determined by combining topographic similarity, cover difference, and terrain difference.

[0025] Further, determining the terrain similarity between the current point and other sampling points based on the terrain coordinates and the surrounding terrain distribution includes:

[0026] Based on the topographic elevation map of the desert grassland restoration area obtained from the geographic information system, the topographic coordinates of the current point and other sampling points on the topographic elevation map are determined.

[0027] Centered on the terrain coordinates, interval points are determined by a preset distance in a preset direction. The elevation difference between the terrain coordinates and the interval points is obtained, and the elevation differences in all preset directions are sorted in a fixed order to obtain the terrain matrix.

[0028] The similarity between the terrain matrix of the current point and other sampling points is determined as the terrain similarity.

[0029] Furthermore, the determination of the salt content consistency coefficient between the current point and other sampling points by combining the similarity of salt ion types and the difference in salt content indicators includes:

[0030] The salt content index of the current point and other sampling points is obtained based on the conductivity meter, and the absolute value of the difference between the salt content indexes is used as the salt content index difference.

[0031] The negative number of the difference in salt content index was normalized to obtain the content similarity.

[0032] The salt content similarity and the salt type similarity are weighted and fused to obtain the salt content consistency coefficient. The values ​​of the salt ion type similarity and the salt content consistency coefficient are normalized values.

[0033] Furthermore, the step of selecting similar points from other sampling points based on the salt consistency coefficient includes:

[0034] Sampling points whose salt consistency coefficient is greater than a preset consistency threshold are taken as similar points of the current point.

[0035] Furthermore, determining the target frequency at the current point at the real-time temperature by combining the optimal measurement frequencies at different temperatures for all similar points includes:

[0036] The average of the best measurement frequencies of all similar points at the current point's real-time temperature is taken as the target frequency for the current point.

[0037] On the other hand, it also includes a soil physicochemical property measurement system for desert steppe restoration, the system including a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the steps of the method as described in any of the foregoing.

[0038] The present invention has the following beneficial effects:

[0039] In this embodiment of the invention, addressing the issue of low accuracy in existing moisture content monitoring due to high salinity in desertified land, the invention employs a method that, under a fixed temperature, combines the true dielectric constant obtained from changes in soil moisture content before and after drying with the apparent dielectric constant of the soil at different oscillation frequencies of an FDR (Frequency Direct Reflectometer). This analysis determines the optimal measurement frequency for each sampling point at different temperatures. Based on the salinity distribution characteristics of desertified grasslands, and considering the geographical differences and vegetation cover differences between the current point and other sampling points, a similarity analysis of salt ion types is performed. This, combined with differences in salinity content indicators, determines a salinity consistency coefficient, effectively analyzing and further eliminating the influence of desertified land salinity, and determining the target frequency for the current point at the real-time temperature. Finally, FDR measurement is performed based on the target frequency to obtain the current dielectric constant, and the moisture content is determined based on this current dielectric constant. This invention integrates the objective characteristics obtained from two different dielectric constants, combined with specific analysis of desertified land salinity content, thereby effectively eliminating the influence of desertified land salinity and improving the accuracy of moisture content monitoring. Attached Figure Description

[0040] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a flowchart of a method for determining the physicochemical properties of soil for desert grassland restoration, provided in one embodiment of the present invention.

[0042] Figure 2 This is a schematic diagram of the dielectric difference index-measurement frequency curve provided in one embodiment of the present invention. Detailed Implementation

[0043] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a method and apparatus for determining the physicochemical properties of soil for desert steppe restoration proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] The following description, in conjunction with the accompanying drawings, details the specific scheme of a method for determining the physicochemical properties of soil for desert grassland restoration provided by this invention.

[0046] Please see Figure 1 The diagram illustrates a flowchart of a method for determining the physicochemical properties of soil for desert steppe restoration, provided by an embodiment of the present invention. The method includes:

[0047] S101: Obtain the vegetation coverage, salinity, and temperature of soil samples taken at different geographical locations in the desert steppe restoration area.

[0048] Most existing methods for measuring soil moisture content involve accurately measuring the apparent dielectric constant of the soil and then calculating the moisture content using empirical formulas (such as the Topp formula). Since the dielectric constant is typically represented by a complex number, its real part represents the soil's ability to store electromagnetic energy, while its imaginary part represents its ability to dissipate electromagnetic energy. Traditional methods for calculating moisture content often neglect the imaginary part of the dielectric constant, using only the real part. However, under ideal conditions (such as pure fresh water), the imaginary part of the dielectric constant is very small, and the sensor reading is almost entirely determined by the real part. Therefore, traditional methods can accurately reflect the soil moisture content.

[0049] However, in reality, desert grassland soils have high salinity, and the imaginary part of the dielectric constant is usually not negligible. When the sensor uses vibration frequency for measurement, a significant amount of electromagnetic energy is dissipated, leading to an overestimation of the final reading. Furthermore, desert grasslands experience large diurnal temperature variations, and under high moisture content, temperature has a significant impact on the imaginary part of the dielectric constant, causing reading deviations. This is especially true under high salinity conditions, where temperature's effect on the imaginary part is very strong, even stronger than its effect on the real part, resulting in higher readings due to increased temperature.

[0050] When using existing sensors based on frequency domain reflection / capacitance method (FDR) to determine the dielectric constant, the actual effect of salt on the dielectric constant and the performance of different salt concentrations at different temperatures are not measured. Only the effect of temperature on the dielectric constant at standard salt concentrations is considered, and the optimal active detection oscillation frequency cannot be determined. This usually results in errors in the dielectric constant reading, ultimately leading to low accuracy in the calculated moisture content.

[0051] Laboratory calibration data acquisition. Based on the soil area of ​​the desert steppe restoration area, multiple different sampling points were evenly set up, and the geographical coordinate parameters of the sampling points and the sealed soil samples were collected.

[0052] Measurement process and data acquisition. At the actual measurement location, the soil salinity index is determined using a conductivity meter, and soil temperature, geographical location information, and remote sensing images are obtained.

[0053] In this embodiment of the invention, vegetation coverage is determined using a 1m x 1m radius around the sampling point. This can be achieved through remote sensing inversion, using remote sensing images. Alternatively, a field quadrat estimation method can be used. The appropriate vegetation coverage analysis method is selected based on the detection requirements and conditions to obtain the vegetation coverage. Alternatively, vegetation pixels can be identified and marked using a 1m x 1m remote sensing image of the measurement location, and the percentage of vegetation pixels can be calculated as the vegetation coverage rate.

[0054] S102: Under a fixed temperature at the sampling point, determine the true dielectric constant based on the change in soil mass before and after drying; adjust the FDR oscillation frequency to obtain the apparent dielectric constant of the soil at different oscillation frequencies; combine the difference between the apparent dielectric constant and the true dielectric constant to determine the optimal measurement frequency; obtain the optimal measurement frequency at different temperatures at the sampling point.

[0055] Changes in salinity increase resistance loss during dielectric constant measurement, leading to measurement errors. Since the dielectric constant is a key parameter in the formula for calculating the final moisture content, this error can cause measurement inaccuracies. Furthermore, because moisture content can typically be calculated in laboratory conditions based on the difference in soil mass before and after drying, and this value is usually the true value, the dielectric constant to be measured can be derived by using the moisture content and dielectric constant formulas. This allows us to understand the effect of different salinities on the dielectric constant.

[0056] Furthermore, in some embodiments of the present invention, determining the true dielectric constant based on the change in soil mass before and after drying includes: dividing the soil at the same sampling point into different sampling groups on an average basis, performing soil drying treatment on each sampling group, determining the true moisture content based on the change in soil mass before and after drying, and converting the true moisture content into the true dielectric constant based on the Topp formula.

[0057] Under laboratory conditions, a small amount of raw soil was sealed and dried at a temperature not lower than 105 degrees Celsius (e.g., 120 degrees Celsius) for at least 24 hours or until the soil mass remained unchanged. The mass of the dried soil was then obtained. Next, the electrodes of the FDR device were inserted into the soil, and an equal amount of deionized water was added to all soil samples. The humidity was kept stable until the mass stabilized again before drying, at which point the soil was sealed.

[0058] The actual moisture content in the experimental scenario is calculated as follows:

[0059] ;

[0060] In the formula, This indicates the true moisture content of the sampled soil in a real-world scenario; This indicates the mass of the soil sample after adding deionized water, inserting electrodes, and sealing it in a laboratory environment (i.e., the mass after reabsorption of water). It can be understood that the experimental sample has a certain baseline mass, and the added deionized water also has a certain mass. The value must be non-zero; otherwise, the experiment cannot be conducted. This indicates the quality after drying.

[0061] In this embodiment of the invention, the true moisture content is the moisture content index obtained under the experimental scenario (drying experiment, fixed temperature, and the added water is deionized water). Its accuracy is high. After determining the true moisture content, the true dielectric constant that should be measured is obtained by reverse calculation using the Topp formula. The Topp formula is a traditional empirical conversion formula between the empirical dielectric constant and moisture content, which will not be elaborated further.

[0062] The reason for adding deionized water is to prevent salt-related ions from affecting the FDR analysis during the experiment.

[0063] During the measurement process, the FDR device can set different oscillation frequencies to excite the resonant frequency of the capacitor. Generally, the higher the preset oscillation frequency, the lower the resistance loss caused by the imaginary part of the dielectric constant. The measured dielectric constant is closer to the real part of the true value. Therefore, the difference between the measured dielectric constant curve (the value measured by the FDR device) at different preset oscillation frequencies and the actual dielectric constant value that should be measured (the value obtained by back-calculation from the moisture content formula) can be obtained by gradually fitting the difference curve until the oscillation frequency represented by the difference value is closest to 0. This indicates that the dielectric constant value measured at the preset oscillation frequency is more consistent with the actual value that needs to be measured.

[0064] Furthermore, in some embodiments of the present invention, adjusting the FDR oscillation frequency to obtain the apparent dielectric constant of the soil at different oscillation frequencies includes: selecting oscillation frequencies according to a preset step size to obtain the measurement frequency; using the FDR to detect the resonant frequency of each measurement frequency based on the measurement frequency; and calculating the apparent dielectric constant based on the resonant frequency and the dielectric constant calculation formula used during instrument factory calibration.

[0065] The preset step size can be, for example, 5MHz. Within the oscillation frequency range of 70MHz-150MHz, a measurement frequency is determined every 5MHz. Based on these measurement frequencies, FDR detection is performed to obtain the corresponding resonant frequency. Then, using the dielectric constant calculation formula from the instrument's factory calibration, the apparent dielectric constant is calculated.

[0066] The most commonly used formula for calculating the dielectric constant during measurement is: Ka represents the apparent dielectric constant of the soil, f represents the resonant frequency measured by the sensor (the resonant frequency cannot be 0 due to the existence of oscillation frequency during the measurement process, otherwise the experimental process would be meaningless), A and B are the calibration coefficients of the sensor, which are determined by the calibration at the time of instrument delivery (such as testing and calibration in air, deionized water, standard solution, etc.), which will not be elaborated further.

[0067] Furthermore, in some embodiments of the present invention, determining the optimal measurement frequency by combining the difference between the apparent dielectric constant and the true dielectric constant includes: calculating the numerical difference between the true dielectric constant and the apparent dielectric constant at different measurement frequencies to obtain a dielectric difference index; constructing a two-dimensional rectangular coordinate system with the dielectric difference index as the vertical axis and the measurement frequency as the horizontal axis, and determining the coordinate points corresponding to the dielectric difference index at different measurement frequencies in the coordinate system; performing curve fitting on all coordinate points based on the least squares fitting method of multiple terms, and extending the fitting until the extended curve intersects the axis with a vertical axis of 0, and taking the measurement frequency under the intersection condition as the optimal measurement frequency.

[0068] Understandably, as the oscillation frequency increases, the resistive loss caused by the imaginary part of the dielectric constant decreases, and the measured apparent dielectric constant gets closer to the real part of the true value. In other words, the apparent dielectric constant is closer to the true dielectric constant value. Therefore, the fitted curve is a curve that gradually decreases. See also... Figure 2 , Figure 2 This is a schematic diagram of the dielectric difference index-measurement frequency curve provided in one embodiment of the present invention.

[0069] In this embodiment of the invention, the preset measurement frequency range is 70MHz-150MHz. However, due to the influence of the imaginary part, the dielectric difference index is still greater than 0 at 150MHz. In order to perform more accurate analysis, this embodiment of the invention can use linear regression to fit and extend the curve, thereby obtaining the measurement frequency (such as 170MHz) corresponding to the dielectric difference index being 0 after fitting. At this time, this measurement frequency is taken as the optimal measurement frequency.

[0070] The optimal measurement frequency characterizes the oscillation frequency with the least influence of the imaginary part under the fitting state at a fixed temperature. Based on the optimal measurement frequency, more accurate and reliable FDR detection results can be obtained at a fixed temperature.

[0071] In this embodiment of the invention, the sealed soil is subjected to heating and cooling treatments with a temperature change step of 1°C. Each time the temperature changes, the optimal measurement frequency at that temperature is re-measured. The temperature variation range can be designed based on the annual limit variation range of the desert steppe surface soil.

[0072] For the same soil sample, the salt content remains constant. Under sealed conditions, the internal water content of the soil does not evaporate with temperature changes. Therefore, the change in the optimal measurement frequency caused by temperature changes is due to salt content.

[0073] S103: Determine the similarity of salt ion types based on the geographical location and vegetation coverage differences between the current point and other sampling points; determine the salt consistency coefficient between the current point and other sampling points by combining the similarity of salt ion types and the differences in salt content indicators; screen similar points from other sampling points based on the salt consistency coefficient; and determine the target frequency of the current point at the real-time temperature by combining the optimal measurement frequencies of all similar points at different temperatures.

[0074] In this embodiment of the invention, the current point is the location where moisture content analysis is to be performed. The current point can be one of the sampling points, or it can be determined within the same desert-steppe restoration area.

[0075] The above steps obtained the optimal measurement frequency of soil samples (which may have different salt contents) at different temperatures under temperature changes. In the actual measurement process, the first step is to determine the consistency between the salt concentration and salt composition of the soil sampled at the current point and other sampling points. The higher the similarity between the two, the more representative the soil measurement properties at the current point can be in the laboratory. Thus, the optimal measurement frequency (i.e., the target frequency) at the current point under the actual temperature can be obtained directly through comprehensive analysis.

[0076] Considering that salt content is determined by measuring the conductivity of the soil solution using a conductivity meter, and that different ions have different compositions (e.g., Ca2+, K+, Na+, SO42-), their conductivity also varies. Therefore, when using conductivity as a comprehensive evaluation index for soil salt content, even if the conductivity index for salt concentration is the same, the types of ions may differ. Furthermore, the salt composition distribution in different desert steppe soils typically exhibits a continuous distribution; in similar areas, the salt composition can generally be considered similar. Therefore, in this embodiment of the invention, the similarity of salt ion types is determined based on the geographical location differences and vegetation cover differences between the current point and other sampling points.

[0077] The geographical location data includes the elevation of the current point and other sampling points, as well as the elevation data of the surrounding terrain. The elevation map of the desert grassland restoration area is obtained from the geographic information system, and the topographic coordinates of the current point and other sampling points on the elevation map are determined. Based on the topographic coordinates and the surrounding terrain distribution, the topographic similarity between the current point and other sampling points is determined. The absolute value of the difference in vegetation coverage between the current point and other sampling points is calculated as the coverage difference, and the absolute value of the difference in elevation is calculated as the terrain difference. Combining the topographic similarity, coverage difference, and terrain difference, the similarity of salt ion species is determined.

[0078] In this embodiment of the invention, terrain similarity represents the degree of similarity in the distribution on the terrain elevation map. It can be understood that the higher the similarity, the higher the consistency of geological influence, that is, the more consistent the content of salt particle types may be.

[0079] Furthermore, in some embodiments of the present invention, determining the terrain similarity between the current point and other sampling points based on the terrain coordinates and the surrounding terrain distribution includes: obtaining a terrain elevation map of the desert grassland restoration area from a geographic information system, determining the terrain coordinates of the current point and other sampling points on the terrain elevation map; determining interval points with a preset distance length in a preset direction centered on the terrain coordinates, obtaining the elevation difference between the terrain coordinates and the interval points, and sorting the elevation differences in all preset directions in a fixed order to obtain a terrain matrix; and determining the similarity of the terrain matrix between the current point and other sampling points as the terrain similarity.

[0080] In this embodiment of the invention, the terrain coordinates are three-dimensional coordinates in a geographic information system, that is, the terrain coordinates are coordinate information in three-dimensional space.

[0081] The preset directions can be due east, due west, due south, due north, due southeast, due northeast, due southwest, and due northwest—eight directions in total. The preset distance can be, for example, 1 meter, or adjusted according to the recognition accuracy of the geographic information system; there are no restrictions on this.

[0082] In this embodiment of the invention, taking the above eight directions as an example, at each preset distance in each direction, a line segment corresponding to the direction is obtained by connecting the line segments, and the other end of the line segment is taken as the interval point. That is, the two ends of the line segment are the interval point and the point corresponding to the terrain coordinates, respectively. The elevation difference between the terrain coordinates and the interval point in the three-dimensional model of the geographic information system is determined, and they are sorted according to a fixed directional order to obtain the terrain matrix.

[0083] The fixed order can be specifically defined as starting with due north and arranging the eight directions clockwise to obtain a fixed direction order.

[0084] In this embodiment of the invention, after obtaining the terrain matrices of the current point and other sampling points, their similarity can be analyzed. Specifically, the Manhattan distance can be used to determine the matrix distance between the terrain matrices of the current point and other sampling points. Then, the negative of the matrix distance is normalized and used as the terrain similarity. Of course, this embodiment of the invention can also use other matrix distances to calculate and normalize the negative of the calculated distance value to obtain the terrain similarity; there is no limitation on this.

[0085] In one embodiment of the present invention, the normalization process can be specifically, for example, maximum and minimum value normalization. Furthermore, the normalization in subsequent steps can all adopt maximum and minimum value normalization. In other embodiments of the present invention, other normalization methods can be selected according to the specific range of the numerical values, which will not be elaborated further.

[0086] Areas with high topographic similarity are generally more likely to have similar salt content and composition due to long-term effects of water flow, etc. However, some vegetation in desert grasslands also has a salt enrichment effect, and salt island effect may occur at plant roots. Therefore, while considering similar topography, it is also necessary to consider the consistency of vegetation coverage. When the surrounding vegetation coverage is closer, the concentration of different types of salts is closer.

[0087] Therefore, in this embodiment of the invention, the absolute value of the difference in vegetation coverage between the current point and other sampling points is calculated as the coverage difference, and the absolute value of the difference in terrain height is calculated as the terrain difference. The larger the values ​​of terrain difference and coverage difference, the greater the geographical difference between the current point and other sampling points, that is, the lower the similarity of salt ion types.

[0088] In summary, by combining topographic similarity, cover difference, and terrain difference, the similarity of salt ion species can be determined. Specifically, this can be achieved by normalizing the topographic similarity, cover difference, and terrain difference to eliminate the influence of dimensions. Then, the product of the normalized cover difference and the normalized terrain difference is calculated, and the difference between the topographic similarity and this product is normalized to obtain the salt ion species similarity.

[0089] Of course, provided that cover difference and terrain difference are negatively correlated with salt ion species similarity, and terrain similarity is positively correlated with salt ion species similarity, other calculation methods can be used. For example, the normalized values ​​of cover difference and terrain difference can be weighted and added together according to actual experimental needs, and the negative of the weighted sum can be normalized to obtain the ecological similarity. Thus, the product of terrain similarity and ecological similarity can be used as the salt ion species similarity. There are no restrictions on this.

[0090] It should be noted that a positive correlation indicates that there is a unidirectional relationship between the independent and dependent variables, where the larger the independent variable is, the larger the dependent variable is; a negative correlation indicates that there is an inverse relationship between the independent and dependent variables, where the smaller the independent variable is, the larger the dependent variable is. The specific manifestation of positive and negative correlations is determined by practical applications, and this application does not impose any special restrictions.

[0091] Furthermore, in some embodiments of the present invention, the salt content consistency coefficient between the current point and other sampling points is determined by combining the similarity of salt ion types and the difference in salt content indicators. This includes: obtaining the salt content indicators of the current point and other sampling points based on a conductivity meter, and taking the absolute value of the difference in salt content indicators as the difference in salt content indicators; calculating the negative number of the difference in salt content indicators and normalizing it as the content similarity; and weighting and fusing the content similarity and type similarity to obtain the salt content consistency coefficient, wherein the values ​​of both the salt ion type similarity and the salt content consistency coefficient are normalized values.

[0092] For the soil dried in the experimental scenario in step S102, a small sample was selected and placed in an open indoor area. After the quality stabilized, five times the mass of deionized water was added at a mass ratio of 1:5. The conductivity was measured using a conductivity meter, and the conductivity was used as a salt content index to characterize the salt ion concentration.

[0093] The salt content index is obtained by conducting experiments on the current point and other sampling points using the same method in the experimental scenario. The absolute value of the difference between the salt content indexes is calculated as the salt content index difference. The larger the value of the salt content index difference, the more inconsistent the salt content of the current point is with that of other sampling points. Therefore, in this embodiment of the invention, the negative number of the salt content index difference is directly calculated and normalized as the content similarity. The content similarity indicates the degree of similarity in salt content between two points.

[0094] In the above process, the similarity of salt ion types has been normalized. By normalizing the similarity of salt ion types, the similarity of content, and the obtained salt consistency coefficient, the data can be standardized, avoiding the result deviation caused by different dimensions.

[0095] The process involves weighted fusion of content similarity and species similarity. Specifically, the weighted fusion can be a weighted sum, where different weights are assigned to content similarity and species similarity in advance according to actual needs (for ease of calculation, the sum of the weights of the two parameters is 1). For example, the weight of content similarity is 0.6 and the weight of species similarity is 0.4. Then, the weighted products are multiplied separately to obtain the corresponding weighted values. Finally, the weighted values ​​of the two parameters are added together to obtain the salinity consistency coefficient.

[0096] The salinity consistency coefficient not only characterizes the consistency of salinity types but also the consistency of salinity content. Therefore, the higher the value, the more similar the salinity influence between the two locations, and similarity points can be screened.

[0097] Similar points are selected from other sampling points based on the salt consistency coefficient, including: sampling points with a salt consistency coefficient greater than a preset consistency threshold are selected as similar points of the current point.

[0098] The preset consistency threshold is a threshold value for the salt consistency coefficient. In this embodiment of the invention, the preset consistency threshold can be, for example, 0.75. This value is obtained by experimental analysis in a specific scenario and can be adjusted according to the actual situation.

[0099] After identifying similar points, the optimal measurement frequency of the current point can be analyzed based on all similar points. The optimal measurement frequency of the current point can be referred to as the target frequency.

[0100] Furthermore, in some embodiments of the present invention, determining the target frequency of the current point at the real-time temperature by combining the optimal measurement frequencies of all similar points at different temperatures includes: taking the average of the optimal measurement frequencies of all similar points at the real-time temperature of the current point as the target frequency of the current point.

[0101] It should be noted that the temperature of the current point is determined, and then the optimal measurement frequency of the pixel at the same temperature is determined. The target frequency is then calculated by combining the optimal measurement frequency at the same temperature.

[0102] In this invention, the target frequency is calculated by averaging. Alternatively, in other embodiments, all similar points can be weighted based on the salt consistency coefficient. First, the salt consistency coefficient of all similar points is processed using the normalized softmax function to obtain the normalized weight. Then, the optimal measurement frequencies of all similar points are weighted and summed based on the normalized weight to obtain the target frequency of the current point.

[0103] S104: Perform FDR measurement based on the target frequency to obtain the current dielectric constant, and determine the water content based on the current dielectric constant.

[0104] The above steps yield the optimal measurement frequency (i.e., target frequency) for the dielectric constant during the measurement process at the current point. At the target frequency, the measured dielectric constant is consistent with the actual requirements.

[0105] Determine whether the target frequency is within the measurement frequency range of the device. If it is within the range, directly select the corresponding target frequency for measurement to obtain the true current dielectric constant. If it is not within the measurement range, perform multiple measurements from the minimum frequency to the maximum frequency according to the device, and perform curve fitting and extension with the frequency as the horizontal axis and the dielectric constant value as the vertical axis (see the above embodiment for the specific fitting and extension process) until the current dielectric constant corresponding to the optimal measurement frequency is reached.

[0106] Then, the local soil moisture content is obtained according to the Topp formula. The Topp formula is described as follows:

[0107] ;

[0108] In the formula, the p-th position is taken as the current point. This represents the actual moisture content at position p during actual measurement; represents the true dielectric constant at position p during actual measurement; a, b, c, and d are empirical fitting parameters of the Top formula, with values ​​of 4.3 × 10⁻⁶. -6 5.5×10 -4 2.92×10 -2 5.3×10 -2 It should be noted that the specific values ​​of the empirical fitting parameters a, b, c, and d are common knowledge. This concludes the determination of the true moisture content for continuous monitoring of actual desertified soils.

[0109] In this embodiment of the invention, addressing the issue of low accuracy in existing moisture content monitoring due to high salinity in desertified land, the invention employs a method that, under a fixed temperature, combines the true dielectric constant obtained from changes in soil moisture content before and after drying with the apparent dielectric constant of the soil at different oscillation frequencies of an FDR (Frequency Direct Reflectometer). This analysis determines the optimal measurement frequency for each sampling point at different temperatures. Based on the salinity distribution characteristics of desertified grasslands, and considering the geographical differences and vegetation cover differences between the current point and other sampling points, a similarity analysis of salt ion types is performed. This, combined with differences in salinity content indicators, determines a salinity consistency coefficient, effectively analyzing and further eliminating the influence of desertified land salinity, and determining the target frequency for the current point at the real-time temperature. Finally, FDR measurement is performed based on the target frequency to obtain the current dielectric constant, and the moisture content is determined based on this current dielectric constant. This invention integrates the objective characteristics obtained from two different dielectric constants, combined with specific analysis of desertified land salinity content, thereby effectively eliminating the influence of desertified land salinity and improving the accuracy of moisture content monitoring.

[0110] On the other hand, a soil physicochemical property determination system for desert steppe restoration is also provided. The system includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of the method as described in any of the foregoing.

[0111] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0112] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A method for determining the physicochemical properties of soil used in desert steppe restoration, characterized in that, The method includes: To obtain soil samples from different geographical locations in the desert steppe restoration area, including vegetation cover, salinity, and temperature. Under a fixed temperature at the sampling point, the true dielectric constant is determined based on the change in soil mass before and after drying; the apparent dielectric constant of the soil at different oscillation frequencies is obtained by adjusting the FDR oscillation frequency; the optimal measurement frequency is determined by combining the difference between the apparent dielectric constant and the true dielectric constant; and the optimal measurement frequency at different temperatures at the sampling point is obtained. Based on the differences in geographical location and vegetation coverage between the current point and other sampling points, the similarity of salt ion types is determined; combining the similarity of salt ion types and the differences in salt content indicators, the salt consistency coefficient between the current point and other sampling points is determined; similar points are selected from other sampling points based on the salt consistency coefficient; and the target frequency of the current point at the real-time temperature is determined by combining the optimal measurement frequencies of all similar points at different temperatures. FDR measurement is performed based on the target frequency to obtain the current dielectric constant, and the water content is determined based on the current dielectric constant. Methods for determining the apparent dielectric constant include: The oscillation frequencies are selected according to the preset step size to obtain the measurement frequencies; based on the measurement frequencies, the resonant frequencies of each measurement frequency are obtained by using FDR detection. Based on the resonant frequency and the dielectric constant calculation formula used during instrument factory calibration, the apparent dielectric constant is calculated. Methods for determining the optimal measurement frequency include: The difference between the true dielectric constant and the apparent dielectric constant at different measurement frequencies is calculated to obtain the dielectric difference index. A two-dimensional rectangular coordinate system is constructed with the dielectric difference index as the vertical axis and the measurement frequency as the horizontal axis. The coordinate points corresponding to the dielectric difference index at different measurement frequencies in the coordinate system are determined. Curve fitting is performed on all coordinate points using the multi-term least squares fitting method, and the fitting is extended until the extended curve intersects the axis with a vertical coordinate of 0. The measurement frequency under the intersection condition is taken as the optimal measurement frequency. The method for determining the salinity consistency coefficient between the current point and other sampling points includes: The salt content index of the current point and other sampling points is obtained based on the conductivity meter, and the absolute value of the difference between the salt content indexes is used as the salt content index difference. The negative number of the difference in salt content index was normalized to obtain the content similarity. The salt content similarity and the salt type similarity are weighted and fused to obtain the salt content consistency coefficient. The values ​​of the salt ion type similarity and the salt content consistency coefficient are normalized values.

2. The method for determining the physicochemical properties of soil for desert steppe restoration as described in claim 1, characterized in that, The determination of the true dielectric constant based on the change in soil mass before and after drying includes: The soil at the same sampling point was divided into different sampling groups. Soil drying was performed on each sampling group. The true moisture content was determined based on the change in soil quality before and after drying. Based on the Topp formula, the true moisture content is converted into the true dielectric constant.

3. The method for determining the physicochemical properties of soil for desert steppe restoration as described in claim 1, characterized in that, The geographical location includes the elevation data of the current point and other sampling points, as well as the elevation data of the surrounding terrain. The determination of salt ion similarity based on the geographical location differences and vegetation coverage differences between the current point and other sampling points includes: Based on the topographic elevation map of the desert grassland restoration area obtained from the geographic information system, the topographic coordinates of the current point and other sampling points on the topographic elevation map are determined. Determine the terrain similarity between the current point and other sampling points based on the terrain coordinates and the surrounding terrain distribution; The absolute value of the difference in vegetation coverage between the current point and other sampling points is calculated as the coverage difference, and the absolute value of the difference in terrain height is calculated as the terrain difference. The similarity of salt ion species was determined by combining topographic similarity, cover difference, and terrain difference.

4. The method for determining the physicochemical properties of soil for desert steppe restoration as described in claim 3, characterized in that, The step of determining the terrain similarity between the current point and other sampling points based on terrain coordinates and the surrounding terrain distribution includes: Based on the topographic elevation map of the desert grassland restoration area obtained from the geographic information system, the topographic coordinates of the current point and other sampling points on the topographic elevation map are determined. Centered on the terrain coordinates, interval points are determined by a preset distance in a preset direction. The elevation difference between the terrain coordinates and the interval points is obtained, and the elevation differences in all preset directions are sorted in a fixed order to obtain the terrain matrix. The similarity between the terrain matrix of the current point and other sampling points is determined as the terrain similarity.

5. The method for determining the physicochemical properties of soil for desert steppe restoration as described in claim 1, characterized in that, The step of selecting similar points from other sampling points based on the salt consistency coefficient includes: Sampling points whose salt consistency coefficient is greater than a preset consistency threshold are taken as similar points of the current point.

6. The method for determining the physicochemical properties of soil for desert steppe restoration as described in claim 1, characterized in that, The process of determining the target frequency at the current point at the real-time temperature by combining the optimal measurement frequencies at different temperatures for all similar points includes: The average of the best measurement frequencies of all similar points at the current point's real-time temperature is taken as the target frequency for the current point.

7. A soil physicochemical property determination system for desert steppe restoration, the system comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1 to 6.

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