Quantitative remote sensing of soil properties

The remote-sensing approach, using satellite and airborne sensors, is rapidly entering the field of environmental sciences as a complementary tool for studying natural processes. This is mainly because the approach enables an overview of large areas simultaneously, using multiple spectral information that correlates with most of the common land cover compositions, on a temporal basis and in a cost-effective way. In soil science, this technique has shown a potential for determining soil groups, the soil genesis process, and soil degradation, and reflects some soil environment interactions as well. Apparently, the limited spectral information provided by the former sensor did not allow the quantitative remote sensing of soils, and thus it could not be used to benefit the future of such endeavors as "precision agriculture". Recent technological developments using remote sensing for monitoring the environment have produced a new approach that is able to provide quantitative rather than qualitative information regarding soil status. This approach, namely, hyper spectroscopy imaging (HSR), is characterized by many spectral channels, which expand the spectral information of the sensed material to be analyzed under quantitative approaches. This technique uses a image spectrometer that has been mounted onboard an aircraft and is able to receive discrete information regarding a sensed target from orbit. It has been successfully used in many disciplines, including geology and marine and vegetative studies. Because this technique holds new capabilities, it opens new frontiers in soil applications as well. The capability of soil spectral information to predict several important soil properties has already been demonstrated under laboratory conditions. Under noncontrolled (field) conditions, difficulties associated with the far-distant position of the sensors relative to the target and with the limited ability to sense only the upper soil crust currently prevent the HSR approach from being simply applied to soils. Only a well-designed HSR approach will be able to provide quantitative soil property maps from such far distances. This paper provides a detailed description of the quantitative (spectral-based)approach for assessing soil properties, using the reflectance radiation across the sun 's illumination range along with an extensive discussion of the obstacles (and their possible solutions)preventing this approach from being a pure laboratory equivalent. Also provided is a detailed review of recent work that has concentrated on quantitative soil remote sensing along with a discussion of the future availability of this technology in terms of cost, physical specifications, and possible applications.