Estimation of Microaggregates of Arid and Semiarid Soils Using Spectral Reflectance in the VNIR-SWIR Region

This paper investigates the relationship between six soil micro aggregate fractions and 74 soil attributes to establish a spectral means for surface-aggregation assessment. The data used in this study were based on the heritage soil spectral library (SSL) of Israel over both semi-arid and arid regions representing seven global soil orders from the USDA list. The database is composed of chemical, physical and spectral measurements. The spectral data consist of reflectance measurements using the IEEE standard protocol across the VIS-NIR-SWIR spectral region, as well as XRF analyses of microelements and XRD determinations, wet chemistry analysis and quantitative assessment of soil mineralogy. The correlation matrix between all attributes enabled isolating four cementation agents (CAs) for soil micro aggregation: clay content, clay mineral species (smectite), organic matter, and free iron oxides. Generating a pedotransfer function (PTF) using these CAs revealed equations that well predict four aggregate size fractions of all soils. A separate spectral-based analysis to evaluate the fraction sizes directly from reflectance measurements without any prior information on the CAs was also generated and revealed highly significant correlations with spectral assignments that belonged to the four selected CAs and their derivatives. We conclude that the micro aggregation stage of soil can be assessed directly or indirectly via PTF, and also by using spectral analysis and data-mining approaches. Assuming that the reflectance information from hyperspectral remote-sensing means such as EMIT (NASA), PRISMA (ASI) and EnMAP (DLR) will soon become readily available, this approach may contribute greatly to the NASA mission's aim to investigate soils as potential dust sources.