Fig 1.
Spatial distribution map of sampling points in the study area and landscape photos.
(a) Spatial distribution of sampling points; (b) Arable land; (c) Garden land; (d–e) Unused land. Note: The Sentinel-2 image used in Fig 1a was obtained from the Copernicus Data Space Ecosystem website (https://browser.dataspace.copernicus.eu/). The sample point data were derived from field surveys, and the county-level point data were determined based on the GPS coordinates of the county centers. Figs 1b-e are field photos taken by Professor Xuemei Wang at representative sampling sites in the Weigan-Kuqa River Oasis in 2022.
Table 1.
The values of each model parameter(s).
Fig 2.
Technical route.
Fig 3.
Sample point proportions, salt distribution, and spectral characteristics of different salinization grades.
Fig 4.
Correlation between mathematically transformed Spectra and SSC.
Fig 5.
Correlation between wavelet coefficients at various scales and SSC under different wavelet transformations.
Fig 6.
Feature band distributions under various spectral transformations.
Fig 7.
Descriptive statistics of SSC in each sample set.
Fig 8.
Accuracy metrics of the SSC estimation model in training and testing Phases.
Note: M1 corresponds to the SVM; M2 to the RF; M3 to the GBDT; M4 to the DF.
Fig 9.
The relative percentage change in performance of the DF model compared to SVM, RF and GBDT on the test set.
Fig 10.
Scatter plot of estimated vs. measured SSC values.
Fig 11.
Number of significantly and extremely significantly correlated bands and the mean |r|.
Note: T1 denotes (1/R)′; T2 denotes R-CWT-27; T3 denotes (1/R)′-CWT-27; T4 denotes R-DWT-H7; T5 denotes (1/R)′-DWT-H8.
Fig 12.
Estimation results of RF models for significantly correlated and extremely significantly correlated bands.
Note: T1 denotes (1/R)′; T2 denotes R-CWT-27; T3 denotes (1/R)′-CWT-27; T4 denotes R-DWT-H7; T5 denotes (1/R)′-DWT-H8.