Inversion of soil salinization at the branch canal scale in the Hetao Irrigation District based on improved spectral indices

The Hetao Irrigation District in Inner Mongolia is a typical arid and semi-arid irrigation district, and the prevention and control of soil salinization has always been a major task in this area. To explore the dynamic changes of soil salinization at the scale of branch canals in the Hetao Irrigation District, a field experiment was conducted in the Zuo Er Branch Canal downstream of the Hetao Irrigation District. The red-edge band and short-wave infrared band are innovatively integrated into the traditional spectral indices for systematic improvement, and the optimal total soil salinity inversion model is constructed through the optimization strategy of different combinations of multiple bands, which effectively enhances the accuracy of soil salinity inversion. The results showed that (1) the remote sensing reflectance spectral curve showed an overall increasing trend with the increase of soil salinization. (2) Compared with the exponential and logarithmic inversion models, the polynomial model for total soil salinity showed a 7.58 % and 34.27 % increase in R², a 15.92 % and 27.68 % increase in RPIQ, a 10.26 % and 23.46 % decrease in MAE, and a 13.56 % and 21.40 % decrease in RMSE, respectively. (3) The improvement spectral indices can improve the accuracy of soil salinity inversion. The polynomial soil total salinity inversion model with the highest accuracy, GSIb model, improved R² and RPIQ by 41.36 % and 42.23 %, and reduced MAE and RMSE by 21.87 % and 29.67 % compared with SI model, which is the optimal soil total salinity inversion model. (4) Compared with the traditional spectral indices, the model constructed by the improved spectral indices was more sensitive to the extreme value of total soil salinity. The study provides an important theoretical basis and reference for the prevention and control of soil salinization in arid and semi-arid regions.