Conventional procedures to determine soil characteristics are time and labor intensive, typically involving multiple processing, extraction and analysis steps. Soil spectroscopy offers a safe and rapid alternative (Figure 1).
Figure 1. Schematic of soil spectroscopy
Soil spectroscopy is the measurement of light absorption when light in the visible, near infrared or mid infrared (Vis–NIR–MIR) regions of the electromagnetic spectrum is applied to a soil surface. The proportion of the incident radiation reflected by soil is sensed through Vis–NIR–MIR reflectance spectroscopy. These characteristic spectra (Figure 2) can then be used to estimate numerous soil attributes including: minerals, organic compounds and water.
Over the last three decades, soil spectroscopy has proven to be a cost- and time-effective, reproducible, nondestructive, and environmental-friendly technique that can be a viable alternative to conventional soil analysis methods. The technique has mainly been used in the laboratory; however, its application in-situ, from air, and from spaceborne sensors is also increasing. Nonetheless there remain challenges, Vis–NIR–MIR spectra include weak, wide, and overlapping absorption bands, which makes identifying specific soil parameters challenging.