Using hyperspectral remote sensing to monitor the properties of
salt-affected soils
Abstract
The aim of the study was to estimate the properties of the salt-affected
soils (SAS) using hyperspectral remote sensing. The study was carried
out on typical SAS from 372 locations covering 17 coastal districts from
west coast region of India. The spectral reflectance of processed soil
samples was recorded in the wavelength range of 350-2500 nm. The full
data set (n=372) was split into two as calibration dataset (n=260, 70%)
to develop the model and validation dataset (n=112, 30%) to evaluate
the performance of the model independently. The spectral data were
calibrated using the laboratory estimated soil properties with five
different multivariate techniques: (a) linear – partial component
regression (PCR) and partial least square regression (PLSR) and (b)
non-linear– multivariate adaptive regression spline (MARS), random
forest (RF) and support vector regression (SVR). In general, the
spectral reflectance from the soils decreased with increasing levels of
salinity (electrical conductivity, EC). The wavelengths, 494, 673, 800,
1415, 1748, 1915, 2207 and 2385 nm showed peculiar absorption
characteristics. The study showed significant achievement in predicting
soil properties like soil pH, salinity (EC), bulk density (BD), soil
available nitrogen (N), exchangeable magnesium (Mg), soil available zinc
(Zn) and boron (B) with acceptable to excellent predictions (ratio of
performance to deviation (RPD) ranged 1.48-2.06). Amongst predicted
models, SVR, PLSR and PCR were found to be more robust than MARS and RF.
The results of the study indicated that the visible near-infrared
spectroscopy has the potential predict properties of the SAS.