Abstract
The ability of thermal and shortwave infrared spectroscopy to characterise composition and texture was evaluated using both particle size separated soil samples and natural soils. Particle size analysis and separation into clay, silt, and sand-sized soil fractions was undertaken to examine possible relationships between quartz and clay mineral spectral signatures and soil texture. Spectral indices, based on thermal infrared specular and volume scattering features, were found to discriminate clay mineral-rich soil from mostly coarser quartz-rich sandy soil and to a lesser extent from the silty quartz-rich soil. Further investigations were undertaken using spectra and information on 51 USDA and other soils within the ASTER spectral library to test the application of shortwave, mid- and thermal infrared spectral indices for the derivation of clay mineral, quartz, and organic carbon content. A nonlinear correlation between quartz content and a TIR spectral index based on the 8.62 μm was observed. Preliminary efforts at deriving a spectral index for the soil organic carbon content, based on 3.4–3.5 μm fundamental H–C stretching vibration bands, were also undertaken with limited results.
Highlights
Mapping and analysing soils for their composition and textural characteristics typically involves extensive field work and laboratory techniques that are traditionally time consuming
MicroFTIR emissivity signatures of raw soil samples confirmed the predominance of quartz and clay minerals
The study of the particle size fractions derived from Tick Hill soil samples show the intimate connection between mineralogy and texture when examining thermal Infrared (TIR) spectra
Summary
Mapping and analysing soils for their composition and textural characteristics typically involves extensive field work and laboratory techniques that are traditionally time consuming. Preliminary results of the TIR spectroscopy investigations undertaken for these Tick Hill soils were presented at the 19th World Congress of Soil Science [25] This publication describes these results in greater detail, and in combination with more results from DHR measurements of USDA (United States Department of Agriculture) soil samples, available via the ASTER Spectral Library (ASL) [26] (http://speclib.jpl.nasa.gov/search-1/soil). Previous investigations of these USDA ASL spectra had found them useful for direct comparisons with field measurements when convolved to ASTER’s 5 band TIR emissivity spectral resolution [27]. This investigation incorporates further interpretation of short wavelength infrared (SWIR) spectroscopy for clay mineral content of all the examined Tick Hill samples
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