## Appendix A  
```
1 Algorithm: Soil Salinity Prediction
2 Input:
3 Spectral data from Landsat 8 OLI (band data)
4 Region of Interest (ROI)
5 Calibration data (soil salinity measurements)
6 Output:
7 Predicted soil salinity values
8 Visualized salt-alkali distribution map
9
10// Step 1: Data Preprocessing
11 Apply radiometric calibration and atmospheric correction to Landsat 8 OLI Level-1
12 Apply scaling factors to Level-1 and Level-2 data
13 Extract band values (e.g., Band R) from the image data
14
15// Step 2: Data Transformation
16 For each band (B, G, R, NIR, SWIR1, SWIR2):
17 Perform mathematical transformations:
18 LOGE_Band = ln(Band)
19 RECI_Band = 1/Band
20 EXP_Band = exp(Band)
21 SQRT_Band = sqrt(Band)
22 DIFF1_Band = first difference of Band (along columns)
23 DIFF2_Band = second difference of Band (along columns)
24 Compute spectral indicators:
25 SI-T = R/NIR \(\times\) 100
26 NDVI = (NIR \(-\) R)/(NIR + R)
27...(other spectral indicators)
28 Spectral_Variables = Original 7 bands + Transformed bands + Spectral indicators
29
30// Step 3: Feature Selection
31 PLSR_selected_features = []
32 For each column in Spectral_Variables:
33 Calculate Pearson correlation between salinity and the column
34 If absolute correlation > 0.4:
35 Add column to PLSR_selected_features
36
37 RF_selected_features = Spectral_Variables
38 BPNN_selected_features = Spectral_Variables
39
40// Step 4: Model Training and Evaluation
41 Split data into training (75%) and testing (25%) sets
42
43// PLSR
44 Create PLSR model
45 Define parameter grid for n_components (e.g., from 1 to 10)

## References

* _[PERSON] et al. (2016)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Prediction of soil surface salinity in arid region of central Iran using auxiliary variables and genetic programming. _Arid Land Res. Manag._**2016**, _30_, 49-64. * [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Detection model of soil salimization information in the Yellow River Delta based on feature space models with typical surface parameters derived from Landsat8 OLI image. _Geomat. Nat. Hazards Risks_**2020**, _11_, 288-300. [CrossRef]* [PERSON] et al. (2019) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Mapping coastal wetland soil salinity in different seasons using an improved comprehensive land surface factor system. _Ecol. Indic._**2019**, _107_, 105517. [CrossRef]
* [PERSON] et al. (2023) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Clonal integration promotes the growth of _Phragmites australis_ populations in saline wetlands of the Yellow River Delta. _Front. Plant Sci._**2023**, _14_, 1162923. [CrossRef] [PubMed]
* [PERSON] et al. (2022) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Biochar and Nitrification Inhibitor (Dicyandiamide) Combination Had a Double-Win Effect on Saline-Alkali Soil Improvement and Soybean Production in the Yellow River Delta, China. _Agronomy_**2022**, _12_, 3154. [CrossRef]
* [PERSON] et al. (2022) [PERSON]; [PERSON]; [PERSON]; [PERSON] Inversion of soil salinity according to different salinization grades using multi-source remote sensing. _Geocarto Int._**2022**, _37_, 1274-1293. [CrossRef]
* [PERSON] and [PERSON] (2020) [PERSON]; [PERSON] A novel approach to quantify soil salinity by simulating the dielectric loss of SAR in three-dimensional density space. _Remote Sens. Environ._**2020**, _251_, 112059. [CrossRef]
* [PERSON] and [PERSON] (2023) [PERSON]; [PERSON] Current Status and Development Trend of Soil Salinity Monitoring Research in China. _Sustainability_**2023**, _15_, 5874. [CrossRef]
* [PERSON] et al. (2023) [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON] Challenges and Opportunities in Remote Sensing for Soil Salinization Mapping and Monitoring: A Review. _Remote Sens._**2023**, _15_, 2540. [CrossRef]
* [PERSON] et al. (2023) [PERSON]; [PERSON]; [PERSON]; [PERSON] Upscaling remote sensing inversion and dynamic monitoring of soil salinization in the Yellow River Delta, China. _Ecol. Indic._**2023**, _148_, 110087.