Diffuse Reflectance Spectroscopy for High-Resolution Soil Sensing

Diffuse reflectance spectroscopy in the visible near-infrared (vis-NIR) and mid-infrared (mid-IR) is a practical analytical technique that can be used for both laboratory and in situ soil analysis. The techniques are sensitive to both organic and mineral soil composition. They are particularly well suited to situations where the primary (conventional) analytical method is laborious and costly or where a large number of analyses and samples are required, e.g. for high-resolution digital soil mapping or precision agriculture. This chapter will describe diffuse reflectance spectroscopy of soil in the vis-NIR (400-700-2,500 nm) and mid-IR (2,500 25,000 nm) portions of the electromagnetic spectrum. The theory of the mechanisms of absorbance in soil will be explained briefly, followed by aspects of data pretreatments, chemometrics, and multivariate calibrations. Finally, both laboratory and in situ applications are discussed and the focus of future research suggested.