Soil moisture sensor calibration method

Abstract

The present invention relates to a method for calibrating a soil moisture sensor. According to the present invention, a soil moisture sensor calibration method comprises the steps of: acquiring one or more soil moisture data at a predetermined range of wavelengths; converting the acquired one or more soil moisture data into a proxy permittivity of a predetermined single wavelength; and using the converted permittivity proxy as input data to an inverse permittivity model that considers organic matter to calculate soil moisture with the bias error caused by organic matter removed. As such, according to the present invention, soil moisture data obtained from one or more wavelengths can be efficiently and accurately calibrated in organic soil without developing a separate calibration algorithm for each wavelength, thereby enabling accurate soil moisture measurement even in soils rich in organic matter.

Description

Technology Field

[0001] The present invention relates to a soil moisture sensor calibration method, and more specifically, to a soil moisture sensor calibration method that converts soil moisture data obtained at one or more wavelengths into a single proxy permittivity at a predefined wavelength and calibrates the soil moisture sensor in organic soil using an organic soil inverse permittivity model at the corresponding wavelength. Background Technology

[0002] In smart farms, sensors that measure soil moisture are used to establish automatic irrigation and monitoring systems.

[0003] Methods for measuring soil moisture using these sensors include the soil moisture tension method, gravimetric method, gypsum block method, neutron moisture measurement method, permittivity measurement method, and electrical resistance measurement method.

[0004] Among these, the dielectric constant measurement method is the most commonly used method for measuring soil moisture. It involves transmitting a signal from the main unit of the measuring equipment, analyzing the characteristics of the reflected waves to determine the soil's dielectric constant, and then measuring the soil moisture content using the correlation between the dielectric constant and the moisture content. This method is based on the principle that the dielectric properties of the soil are determined by the amount of water within the soil.

[0005] However, existing permittivity measurement methods have limitations in that calibration is difficult and calibration accuracy is low at one or more wavelengths, particularly in wavelength ranges more sensitive to organic matter, requiring the development of separate calibration algorithms for each wavelength of soil moisture data.

[0006] Furthermore, existing models determine the maximum permittivity of bound and free water by considering only soil clay content, whereas the actual permittivity of soil is also significantly influenced by organic matter content.

[0007] Therefore, existing models have a limitation in that they cannot reflect organic matter in setting the maximum permittivity, which can lead to reduced accuracy in soil moisture estimation in soils with very high or very low organic matter content. Prior art literature

[0008] Korean Registered Patent No. 10-1911210 The problem to be solved

[0009] According to the present invention, the purpose is to provide a soil moisture sensor calibration method that converts soil moisture data obtained at one or more wavelengths into a single proxy permittivity at a predefined wavelength and calibrates a soil moisture sensor in organic soil using an inverse permittivity model of organic soil at the corresponding wavelength. means of solving the problem

[0010] According to one embodiment of the present invention for achieving such technical challenges, a soil moisture sensor calibration method comprises: a step of acquiring one or more soil moisture data at a predetermined range of wavelengths; a step of converting the acquired one or more soil moisture data into a proxy permittivity of a predetermined single wavelength; and a step of using the converted permittivity proxy as input data to an inverse permittivity model that considers organic matter to calculate soil moisture with the bias error caused by organic matter removed. Effects of the invention

[0011] As such, according to the present invention, soil moisture data obtained from one or more wavelengths can be efficiently and accurately calibrated in organic soil without developing a separate calibration algorithm for each wavelength, thereby enabling accurate soil moisture measurement even in soils rich in organic matter. Brief explanation of the drawing

[0012] Figure 1 is a diagram illustrating a method for estimating soil moisture. FIG. 2 is a diagram illustrating the flow of a soil moisture sensor calibration method according to one embodiment of the present invention. FIG. 3 is a diagram illustrating the step of acquiring soil moisture data according to one embodiment of the present invention. FIG. 4 is a diagram illustrating the step of generating a dielectric constant proxy according to one embodiment of the present invention. FIG. 5 is a drawing illustrating the step of correcting soil moisture according to one embodiment of the present invention. FIG. 6 is a diagram illustrating an example comparing a permittivity proxy-based correction and a general correction at a wavelength of 100 MHz according to one embodiment of the present invention. Specific details for implementing the invention

[0013] Preferred embodiments according to the present invention will be described in detail below with reference to the attached drawings. In this process, the thickness of lines or the size of components shown in the drawings may be exaggerated for clarity and convenience of explanation.

[0014] Furthermore, the terms described below are defined in consideration of their functions within the present invention, and these may vary depending on the intent or practice of the user or operator. Therefore, the definitions of these terms should be based on the content throughout this specification.

[0015] Figure 1 is a diagram illustrating a method for estimating soil moisture.

[0016] First, with reference to FIG. 1, a method for estimating soil moisture using a permittivity model in the present invention will be described.

[0017] First, calculate the effective permittivity of completely dry organic soil using the following mathematical formula 1.

[0018]

[0019] At this time, is the effective dielectric constant of dry organic soil, and is the permittivity of clay, and is the volume ratio of clay, and is the permittivity of sand, and is the volume ratio of sand.

[0020] also, is the silt permittivity, and is the volume ratio of silt, and is the organic permittivity, and is the volume ratio of organic matter.

[0021] At this time, It is calculated as shown in mathematical formula 2 below.

[0022]

[0023] In this case, SOM is the weight ratio of organic matter, and is the volume density of organic matter, and is the volumetric density of inorganic soil.

[0024] In addition, organic matter weight ratio It can be converted into an organic carbon weight ratio OC as shown in mathematical formula 3 below.

[0025]

[0026] At this time, is the conversion coefficient.

[0027] In addition, wilting point for estimating soil moisture (SM) is calculated as in the following mathematical formula 4, and the saturation point p is calculated as in the following mathematical formula 5.

[0028]

[0029]

[0030] When soil moisture is below the wilting point, bound water acts predominantly due to the charge of soil particles, attracting water molecules to the surface of the particles and forming a thin layer of moisture around mineral particles and organic tissue.

[0031] As the amount of water in the soil increases, this moisture layer becomes thicker, and the van der Waals force becomes dominant over the charge on the particle surface.

[0032] In the case where only such bound water exists, the soil moisture when the soil moisture is less than the wilting point (through the following mathematical formula 6) Estimates )

[0033]

[0034] In addition, when soil moisture is greater than the wilting point and less than the saturation point, the permittivity of water in the soil appears as a complex of the permittivity of bound water and free water, and through the following Equation 7, the soil moisture when it is between the wilting point and the saturation point ( Estimates )

[0035]

[0036] In addition, when soil moisture is above the saturation point, bound water no longer exists and all moisture becomes free water, and through the following mathematical formula 8, the soil moisture when soil moisture is above the saturation point ( Estimates )

[0037]

[0038] Since soil moisture is the subject of estimation, a model based on the range of soil moisture cannot be applied. However, soil moisture is estimated using all three models based on the observed permittivity, and then soil moisture in the discontinuous model is estimated by selecting the model with the second largest soil moisture value among them, as shown in Equation 9 below.

[0039]

[0040] Hereinafter, a soil moisture sensor calibration method according to an embodiment of the present invention will be described in detail with reference to FIGS. 2 to 5.

[0041] FIG. 2 is a diagram illustrating the flow of a soil moisture sensor calibration method according to an embodiment of the present invention, FIG. 3 is a diagram explaining the step of acquiring soil moisture data according to an embodiment of the present invention, FIG. 4 is a diagram explaining the step of generating a dielectric constant proxy according to an embodiment of the present invention, and FIG. 5 is a diagram explaining the step of calibrating soil moisture according to an embodiment of the present invention.

[0042] As illustrated in FIGS. 2 and 3, a soil moisture sensor calibration method according to one embodiment of the present invention first acquires one or more soil moisture data at a wavelength within a preset range (e.g., 50 MHz to 18 GHz) (S110).

[0043] In this case, it is assumed that the bias error due to the applied organic matter uncertainty is equally reflected within the error range pre-set for soil moisture.

[0044] In other words, soil moisture data is obtained without considering variables caused by organic matter.

[0045] In this case, soil moisture data can be measured using sensors including TDR (Time Domain Reflectometry) or FDR (Frequency Domain Reflectometry).

[0046] Next, as shown in FIG. 4, one or more acquired soil moisture data are converted into a preset single wavelength (e.g., 50 MHz) proxy permittivity (S120).

[0047] More specifically, one or more acquired soil moisture data are subjected to a permittivity proxy calculation using the following mathematical formula 10 for additional correction by organic matter.

[0048]

[0049] At this time, represents the soil moisture value observed by a soil moisture sensor in a wavelength range of a preset range (e.g., 50 MHz to 18 GHz), and is a permittivity proxy.

[0050] In this case, the soil moisture value observed by the soil moisture sensor is the parameter of the regression model between the observed soil moisture and permittivity values, which is obtained using a second-order polynomial-based regression model (e.g., the Seyfried model) so that the error becomes zero. , and Determines.

[0051] For example, when simulating permittivity after inputting the actually observed soil moisture weight formula into the SM of a second-order polynomial in SMAPVEX12, the parameters of the regression model that have the minimum error with the actual 50MHz permittivity observation are , and am.

[0052] The parameters of the regression model determined in this way will, in the future, use soil moisture values ​​observed at one or more wavelength ranges as a permittivity proxy ( It converts it to ).

[0053] Next, the converted permittivity proxy is used as input data for an inverse permittivity model that considers organic matter to calculate soil moisture with the bias error caused by organic matter removed (S130).

[0054] More specifically, first, dielectric information is obtained by using a dielectric proxy converted into an inverse dielectric model, which is a model of maximum dielectric constant for bound water and free water considering soil clay content and organic matter content as shown in Equation 11 below, as input data.

[0055]

[0056]

[0057]

[0058]

[0059] At this time, is the maximum permittivity of the number of bonds, and ε is the maximum permittivity of free water, OM is the organic matter content, and , , , , , is an empirical constant.

[0060] The empirical constant is determined based on the observational data on which it is based; in the case of SMAPVEX12 observational data, , , , , and It is determined as.

[0061] Next, in Equation 10 and Equation 11 , , After calculating, the calculated , , By applying to mathematical formulas 6 through 8 , , Calculate, , , The second value among them is determined as the final soil moisture.

[0062] FIG. 6 is a diagram illustrating an example comparing a permittivity proxy-based correction and a general correction at a wavelength of 100 MHz according to one embodiment of the present invention.

[0063] As shown in Fig. 6, the soil moisture sensor can be calibrated with a 50 MHz-based dielectric model without developing a dielectric model including organic matter at a 100 MHz wavelength.

[0064] As such, according to the present invention, soil moisture data obtained from one or more wavelengths can be efficiently and accurately calibrated in organic soil without developing a separate calibration algorithm for each wavelength, thereby enabling accurate soil moisture measurement even in soils rich in organic matter.

[0065] The present invention has been described with reference to the embodiments illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the following claims.

Claims

Claim 1 The method comprises: a step of acquiring one or more soil moisture data at a preset range of wavelengths corresponding to the measurement frequency band of a soil moisture measuring sensor; a step of converting the acquired one or more soil moisture data into a preset single-wavelength proxy permittivity corresponding to the reference frequency of an inverse permittivity model considering organic matter; and a step of using the converted permittivity proxy as input data to the inverse permittivity model considering organic matter to calculate soil moisture with the bias error caused by organic matter removed, wherein the step of converting into a single-wavelength proxy permittivity comprises the following mathematical formula for additional correction due to organic matter for the acquired one or more soil moisture data Perform permittivity proxy calculations through, and is a soil moisture value observed by a soil moisture sensor in a preset wavelength range, and is a permittivity proxy, and , and A soil moisture sensor calibration method that is a parameter of a regression model between soil moisture and permittivity observations. Claim 2 In claim 1, the step of acquiring one or more soil moisture data is a soil moisture sensor calibration method for acquiring soil moisture data that does not consider variables caused by organic matter. Claim 3 In claim 1, the soil moisture data is a soil moisture sensor calibration method in which the sensor is measured using a sensor including TDR (Time Domain Reflectometry) or FDR (Frequency Domain Reflectometry). Claim 4 delete Claim 5 In claim 1, the above-mentioned inverse permittivity model is a soil moisture sensor calibration method in which the model is a maximum permittivity model for bound water and free water considering soil clay content and organic matter content as shown in the following mathematical formula: At this time, is the maximum permittivity of the number of bonds, and ε is the maximum permittivity of free water, OM is the organic matter content, and , , , , , is a pre-established empirical constant.

Images