Spectral Characterization of Parent Soils From Globally Important Dust Aerosol Entrainment Regions

We investigated the variation in the mineralogical composition of surface soil samples from a wide range of atmospheric dust aerosol generating regions. These soils likely have mineral compositions similar to dust aerosols. We measured the visible, shortwave infrared (VSWIR) and long wave infrared (LWIR) reflectance spectra, as well as LWIR transmission spectra and carried out linear spectral mixture modeling on the transmission data. The spectroscopically identified minerals were compared with the mineralogy previously obtained using X-ray diffraction (XRD) and optical microscopy (OM). The results showed that VSWIR is very sensitive to iron-bearing minerals and better identifies their presence and type compared to XRD and OM. Clay minerals and carbonates have multiple distinct absorptions features in SWIR but are often overlapping, limiting our ability to uniquely assign spectral features. LWIR reflectance easily distinguishes carbonates, even in trace amounts that were not identified with other techniques. LWIR reflectance spectra for silicates were more complicated to interpret. In some samples, we were able to identify Si-O features diagnostic of common silicates; however, in most cases these features were absent, and an unusual new peak (similar to 7.4-7.9 mu m) was observed. LWIR transmission is characterized by strong absorption that arises from overlapping features from multiple silicate minerals, but carbonates are readily identifiable. Spectroscopy is complementary to XRD and can help identify additional minerals in these soil samples. Our results can help improve global soil atlases and can be used to support interpretation and validation of data acquired by current and future remote sensing instruments. Plain Language Summary We measured global surface soils, whose composition is likely similar to atmospheric dust aerosols, in visible, shortwave and longwave infrared reflectance and transmission to determine their mineralogy. Spectroscopy is complementary to other techniques and often better identified specific minerals in these samples. These measurements can be used to improve global soil atlases and to support interpretation of data from current and future remote sensing instruments.

Automated summary

We investigated the mineralogy of global surface soils, which are likely similar to atmospheric dust aerosols, using reflectance and transmission measurements in visible, shortwave, and longwave infrared regions. Spectroscopy proved to be complementary to other techniques and exhibited better identification of specific minerals in these samples. Our findings can contribute to the enhancement of global soil atlases and the interpretation of data obtained from remote sensing instruments.