We wish to estimate the amount of
carbon (C) stored in the soil
at high altitudes, for which there is little information. Collecting
and transporting large numbers of soil samples from such terrain are
difficult, and we have therefore evaluated the feasibility of scanning
with visible near-infrared (vis-NIR) spectroscopy in situ for the
rapid measurement of the soil in the field. We took 28 cores (≈1 m depth and 5 cm diameter)
of soil at altitudes from 2900 to 4500 m in the Sygera Mountains on
the Qinghai–Tibet Plateau, China. Spectra were acquired from
fresh, vertical faces 5 × 5 cm in area from the centers of the
cores to give 413 spectra in all. The raw spectra were pretreated
by several methods to remove noise, and statistical models were built
to predict of the organic C in the samples from the spectra by partial
least-squares regression (PLSR) and least-squares support vector machine
(LS-SVM). The bootstrap was used to assess the uncertainty of the
predictions by the several combinations of pretreatment and models.
The predictions by LS-SVM from the field spectra, for which <i>R</i><sup>2</sup> = 0.81, the root-mean-square error RMSE =
8.40, and the ratio of the interquartile distance RPIQ = 2.66, were
comparable to the PLSR predictions from the laboratory spectra (<i>R</i><sup>2</sup> = 0.85, RMSE = 7.28, RPIQ = 3.09). We conclude
that vis-NIR scanning in situ in the field is a sufficiently accurate
rapid means of estimating the concentration of organic C in soil profiles
in this high region and perhaps elsewhere
