Soil degradation monitoring by remote sensing: Examples with three degradation processes

Recent developments in the monitoring of soil degradation processes have used passive remote sensing (diffuse reflectance spectroscopy) and active remote-sensing tools such as ground-penetrating radar (GPR) and frequency domain electromagnetic induction (FDEM). We have limited our review to three important degradation processes: structural crust, salinity, and soil mineral deformation and alterations caused by fire. These degradation processes, leading to declines in soil fertility and productivity, are commonly viewed in terms of their spatial and temporal distribution and variability, making spatial monitoring tools such as remote sensing the preferred choice. Recent work has shown that a hyperspectral (narrow-bands) approach combined with active remote sensing (FDEM and GPR) can be used to provide detailed, three-dimensional maps of soil salinity status in croplands. Such a map could improve our understanding of salinization mechanisms and salt sources, leading to improved drainagesystem planning and management. Another pronounced hazard is structural crust formation following rainstorm events, which decreases soil infiltration, accelerates water runoff, and increases the potential for soil erosion. The spatial distribution of soil infiltration can be assessed using spectral information. Finally, recent studies have shown the potential of hyperspectral spectroscopy to assess and monitor mineralogical, chemical, and physical changes, some irreversible, in post-fire soils. The irreversible changes may serve as a footprint of fire intensity but may also affect the burned ecosystem's recovery. This review should serve as a precursor for future innovative studies of soil degradation processes as well as to open up a new frontier for soil preservation using hyperspectral technology.