Scientia Agricultura Sinica ›› 2025, Vol. 58 ›› Issue (6): 1159-1172.doi: 10.3864/j.issn.0578-1752.2025.06.009

• SOIL & FERTILIZER·WATER-SAVING IRRIGATION·AGROECOLOGY & ENVIRONMENT • Previous Articles     Next Articles

A Method for Estimating Water-Salinity Information of Soil Surface Using RGB and Texture Features

SONG Yan1,2(), CHAI MingTang1,2(), LI WangCheng1, SUN LiYing1, Wulianen Saiernu1, DU TianZe1   

  1. 1 School of Civil and Hydraulic Engineering, Ningxia University, Yinchuan 750021
    2 Ningxia Key Laboratory of the Internet of Water and Digital Water Governance of the Yellow River, Yinchuan 750021
  • Received:2024-05-07 Accepted:2024-06-11 Online:2025-03-25 Published:2025-03-25
  • Contact: CHAI MingTang

Abstract:

【Objective】 Saline soil poses a global ecological challenge. The rapid and precise monitoring of surface soil water and salt information was crucial for effective control and remediation of soil salinization. 【Method】 The present study proposed a quantitative estimation method, which combined high-precision optical remote sensing and image digital processing technology at a small scale, to predict soil water content and salt content based on soil apparent color parameters (RGB) and texture feature values. Firstly, the calibration of the soil multi-parameter sensor was based on the relationship between dielectric constant and water content, electrical conductivity, and salt content. Secondly, the image digital processing technology was employed to extract the RGB and texture features of the soil. The most relevant variables were determined through correlation analysis, and an optimal fitting model incorporating RGB, texture features, water content, and salt content was constructed. Finally, the accuracy of the inversion method was verified using the sensor approach.【Result】 The trivariate regression model, which fitted the water content and RGB, exhibited the most optimal fitting effect with an R2 value of 0.97. For the fitting of salt content to RGB and texture features, a one-variable polynomial model incorporating salt content and soil apparent white ratio demonstrated superior fitting performance when the salt content was greater than or equal to 6%, yielding an R2 value of 0.97. Conversely, for salt content below 6%, the autocorrelation (AUT) fitting between salt content and texture feature values was proved to be the most effective approach with an R2 value of 0.93. Upon comparing and calculating the water content and salt content obtained through both multi-parameter sensor calibration method and the inversion method proposed in this paper, it was observed that relative error ranges for water content measurement using these two methods fell within 0.27%-9.48%, while relative error ranges for salt content ranged from 0.07% to 8.64%. In both cases, the absolute errors remained below 1%. 【Conclusion】 The present study presented a methodology for the inversion of soil apparent water and salt information, thereby establishing a theoretical foundation and offering the technical support for the rapid and precise determination of soil surface water and salt.

Key words: image processing, frequency domain reflectometry (FDR), soil apparent color parameters (RGB), texture features, soil water and salt content

Fig. 1

Schematic diagram of soil multi-parameter sensor"

Table 1

The performance of soil multi-parameter sensor"

参数 Parameter 测量范围 Measurement range 分辨率 Resolution ratio 测量精度 Measurement accuracy
介电常数 Dielectric constant 0.88—81.88 0.1 1
电导率 Electrical conductivity 0—20 dS·m-1 0.01 dS·m-1 ±5%
温度 Temperature -40.00—80.00 ℃ 0.1 ℃ ±0.5 ℃

Fig. 2

Soil multi-parameter sensor calibration test process"

Table 2

Experimental design for extraction of soil apparent RGB and texture features under varied water and salt content"

测定项目 Item 质量含水量Moisture content (%) 含盐量Salt content (%)
土壤含水量 T1 0、2、4、6、8、10、12、14、16、18 0、2
土壤含盐量 T2 4、6 0、2、4、6、8、10、12、14、16、18

Table 3

The texture features in this paper"

纹理特征
Texture feature
名称
Name
描述
Description
公式
Formula
MEA 均值
Mean
纹理的平均情况
Average situation of texture
$M E A=\sum_{i=0}^{N-1} \sum_{j=0}^{N-1} i \times p(i, j)$
STD 标准差
Standard deviation
图像中像素值的变化程度
The degree of change of pixel value in the image
$S T D=\sqrt{\sum_{i} \sum_{j} p(i, j) \times(i-M E A)^{2}}$
VAR 方差
Variance
纹理变化的大小
The size of texture change
$V A R=\sum_{i} \sum_{j}(i-M E A)^{2} p(i, j)$
CON 对比度
Contrast
纹理的清晰度
The clarity of texture
$C O N=\sum_{n=0}^{N g-1} n^{2}\left\{\begin{array}{c} \sum_{i=1}^{N g} \sum_{j=1}^{N g} p(i, j) \\ |i-j|=n \end{array}\right\}$
DIS 非相似性
Dissimilarity
图像中灰度级对之间的差异性
The difference between gray level pairs in the image
$D I S=\sum_{i} \sum_{j} p(i, j) \times|i-j|$
HOM 均一性
Homogeneity
局部纹理同质性
Local texture homogeneity
$H O M=\sum_{i} \sum_{j} \frac{1}{1+|i-j|} p(i, j)$
ASM 角二阶矩
Angle two matrix
图像中纹理的均匀性和清晰度
The uniformity and clarity of the texture in the image
$A S M=\sum_{i} \sum_{j}\{p(i, j)\}^{2}$
ENR 能量
Energy
图像灰度分布均匀程度和纹理粗细度
Image gray distribution uniformity and texture thickness
$E N R=\sum_{i} \sum_{j}\{p(i, j)\}^{2}$
MAX 最大值
Maximum value
图像中最明显或最突出的纹理元素的强度或尺度 The intensity or scale of the most obvious or prominent texture element in the image $M A X=\max \{p(i, j)\}$
ENT
Entropy
图像中纹理的非均匀程度或复杂程度
The non-uniformity or complexity of the texture in the image
$E N T=-\sum_{i} \sum_{j} p(i, j) \log (p(i, j))$
COR 相关性
Correlation
纹理的一致性
Texture consistency
$C O R=\frac{\sum_{i} \sum_{j}(i, j) p(i, j)-\mu_{x} \mu_{y}}{\sigma_{x} \sigma_{y}}$
IDM 逆差矩
Inverse difference moment
图像纹理的同质性,度量图像纹理局部变化的多少
The homogeneity of image texture measures the local change of image texture
$I D M=\sum_{i} \sum_{j} \frac{1}{1+(i-j)^{2}} p(i, j)$
AUT 自相关
Autocorrelation
纹理的粗细度及方向性等特征参数
Feature parameters such as texture thickness and directionality
$A U T=\sum_{i} \sum_{j} i \times j \times p(i, j)$

Table 4

Experimental design for accuracy verification of water-salt information inversion under varied water and salt content"

编号
Numbering
含水量
Water content (%)
含盐量
Salt content (%)
1 2 4、6、8
2 4
3 6
4 8

Fig. 3

The relationship between volumetric water content and dielectric constant of different sensors"

Table 5

Calibration parameters of conductivity and salt content of different sensors"

探头序号
Probe serial number
参数a
Parameter a
决定系数
Coefficient of determination (R2)
1 4.3305 0.90
2 0.6691
3 4.0943
4 0.8464
5 -6.5299
6 -14.9267

Fig. 4

The relationship between salt content and conductivity of different sensors"

Fig. 5

Partial texture features of 0 water content and 0 salt content (a) and 4% water content and 6% salt content (b)"

Fig. 6

The R2 between water content (a), salt content (b) and texture features"

Table 6

Pearson correlation analysis between RGB features and soil water content"

样本数
Number of samples
参数
Parameter
R2 Sig.
10 R -0.93 <0.01
G -0.94
B -0.91

Fig. 7

Apparent photographic images of soil sample barrels with different water contents"

Table 7

Evaluation metrics of principal component analysis for soil water content and apparent color parameters (R, G, B)"

名称Name 意义Meaning 结果Result
KMO检验
KMO test
测量变量之间的共同度,即共享的统计变异量
The commonality between the measured variables, that is, the shared
statistical variation
KMO=0.82,适合进行因子分析
KMO=0.82, which is suitable for factor analysis
巴特利特检验
Bartlett test
评估变量之间的相关性是否足够支持进行主成分分析
To assess whether the correlation between variables is sufficient to support principal component analysis
Sig.值(显著性概率)小于0.001
The Sig. value (probability of significance) is less than 0.001
总方差解释
Total variance explanation
衡量各主成分对原始数据信息的解释的重要指标
An important indicator to measure the interpretation of the original data information by each principal component
R、G、B三者的总方差解释为99.71%
The total variance of R, G and B is 99.71%
Durbin-Waston检验
Durbin-Waston test
检验回归分析中残差的一阶自相关
Test the first-order autocorrelation of residuals in regression analysis
Durbin-Waston=2.13, 不存在自相关性
Durbin-Waston=2.13,no autocorrelation exists

Table 8

The correlation model of soil water content inversion based on RGB and texture features"

自变量
Independent variable
线性回归方程
Equation of linear regression
模型检验 Model calibration
R2 RMSE
AUT y=6817.6×AUT2-204398×AUT+5×106 0.89 3.1801×1011
R y=-0.2599×R+48.1690 0.96 1.17
G y=-0.2620×G+39.3632 0.95 1.21
B y=-0.2690×B+32.2558 0.96 1.16
R、G、B y=-0.097×R-0.052×G-0.118×B+39.874 0.97 0.85

Fig. 8

Apparent photographic images of soil sample barrels with different salt contents"

Table 9

The correlation model of salt content inversion based on RGB and texture features"

含盐量
Salt content
自变量
Independent variable x
模型方程
Model equation
R2 RMSE
≥6% 含盐量白色占比
Salt content of white proportion
y=2.8720x+2.7696 0.91 1.62
y=3.2606lnx+8.6280 0.88 5.96
y=-0.3396x2+4.7752x+1.3118 0.97 0.85
<6% 纹理特征
Texture features
y=1.919×10-17AUT3-2.522×10-10AUT2+0.001AUT-1602.839 0.93 9.18
y=-42720.899MAX3+28956.138MAX2-623.716MAX+5.737 0.71 39.13
y=6.35×1013COR3-1.27×1014COR2+6.351×1013COR+81.921 0.77 38.26

Fig. 9

Comparison of soil volumetric water content and salt content based on RGB and texture feature inversion with multi- parameter sensor values"

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