Quantitative Estimation of Soil Salinization in an Arid Region of the Keriya Oasis Based on Multidimensional Modeling

Abstract

Soil salinity is one of the major factors causing land degradation and desertification on earth, especially its important damage to farming activities and land-use management in arid and semiarid regions. The salt-affected land is predominant in the Keriya River area of Northwestern China. Then, there is an urgent need for rapid, accurate, and economical monitoring in the salt-affected land. In this study, we used the electrical conductivity (EC) of 353 ground-truth measurements and predictive capability parameters of WorldView-2 (WV-2), such as satellite band reflectance and newly optimum spectral indices (OSI) based on two dimensional and three-dimensional data. The features of spectral bands were extracted and tested, and different new OSI and soil salinity indices using reflectance of wavebands were built, in which spectral data was pre-processed (based on First Derivative (R-FD), Second Derivative (R-SD), Square data (R-SQ), Reciprocal inverse (1/R), and Reciprocal First Derivative (1/R-FD)), utilizing the partial least-squares regression (PLSR) method to construct estimation models and mapping the regional soil-affected land. The results of this study are the following: (a) the new OSI had a higher relevance to EC than one-dimensional data, and (b) the cross-validation of established PLSR models indicated that the β-PLSR model based on the optimal three-band index with different process algorithm performed the best result with R2V = 0.79, Root Mean Square Errors (RMSEV) = 1.51 dS·m−1, and Relative Percent Deviation (RPD) = 2.01 and was used to map the soil salinity over the study site. The results of the study will be helpful for the study of salt-affected land monitoring and evaluation in similar environmental conditions.

Possibility of Zhuhai-1 Hyperspectral Imagery for Monitoring Salinized Soil Moisture Content Using Fractional Order Differentially Optimized Spectral Indices

“…In some other studies, it was also concluded that optimized spectral indices combined with spectral transformation could achieve better modeling results and had good inversion feasibility [30,31]. Nijat et al used the multi-dimensional modeling method to quantitatively retrieve the SSC on the basis of the WorldView-2 multi-spectral imagery [32], and the results obtained were consistent with the views of Li. that the ANN model was a powerful tool for inversion of SOC in farmland areas [7].…”

“…Partial least squares (PLS) is a mathematical optimization technique that finds the best function match for a set of data by minimizing the sum of squares of errors [32]. PLSR ≈ MLR + canonical correlation analysis (CCA) + principal component analysis (PCA).…”

“…In addition, AIC, as an index to evaluate the efficiency of the model can weigh the complexity of the estimated model and the goodness of the model fitted to the data. The smaller the value of AIC, the better the model can explain the data with the least free parameters, making it better at avoiding overfitting [32].…”

Special Issue “Focus on the Salinization Issue in the Mediterranean Area”

“…The main goal of this Special Issue of Water is to focus on different methodological approaches to improve the understanding of salinization mechanisms of both groundwater and soil water, which may derive from actual seawater intrusion, paleo-seawater intrusion, an increase in atmospheric temperatures that in turn drives evapoconcentration and agricultural return flows. From its first announcement, and after being thoroughly peer reviewed, six papers have been accepted for publication [10][11][12][13][14][15]. To gain an overview of the ideas collected by this Special Issue, a brief summary of each published paper is reported below.…”

“…Another contribution of this Special Issue tackles complex transboundary aquifer management affected by different sources of salinization that threaten the well field of the Lower Yarmouk Gorge (LYG) shared by Israel, Jordan and Syria [13]. In a different line of research, the study presented by Kasim et al [14] analyzed the salt-affected land which is predominant in the Keriya River area of Northwestern China via satellite band reflectance and newly optimum spectral indices (OSIs) based on two-dimensional and three-dimensional data. Finally, a review paper closes this Special Issue discussing the new advances and challenges that still must be faced in the Mediterranean with a special focus on predictions of climate change effects on coastal aquifers, which surely deserve additional research [15].…”