Fig. 1. Distribution of soil samples in sampling area

Fig. 2. Average reflectance spectra of dry soil samples with different salt contents

Fig. 3. Average reflectance spectra of salinity soil samples with different moisture contents (soil salt content approaching 35 g·kg^-1)

Fig. 4. Estimation models for soil salt content under the condition of moisture interfered
(a): PLSR modeling result; (b): PLSR validation result; (c): PDS-PLSR modeling result;(d): PDS-PLSR validation result; (e): OSC-PLSR modeling result; (f): OSC-PLSR validation result

Fig. 5. The variable importance in the projection (VIP) of the (a) PLSR; (b) PDS-PLSR; and (c) OSC-PLSR modeling and the Spearman correlation between the soil salt content and the soil spectral reflectance by (a) First derivative spectral curve; (b) PDS transferring and (c) OSC filtering based on the first derivative spectral data