A semi-empirical approach to quantify and handle the effect of moisture on spectral unmixing

Abstract

Spectral unmixing techniques aim to retrieve the abundances of the materials contributing to a spectral measurement by inverting the underlying spectral mixture occurring at the surface level. In environment and Earth sciences, the darkening effect of moisture on soils and rocks is a common challenge that may lead to major errors when neglected. In this study, a linear function was calibrated to relate a single moisture index to its spectral effect. The function was then combined with the Neighbor-Band Ratio Unmixing (NBRU) and the Linear Spectral Unmixing (LSU) approaches and applied on spectra of a crafted mixture and a rock sample acquired in laboratory conditions, and on a WorldView-3 (WV3) superspectral image of the Canadian Malartic open pit mine. In laboratory conditions, the addition of the moisture function led to a higher stability and a lower deviation of the abundances retrieved with varying water contents (WC). The combined method also obtained a moisture map of the Mine Canadian Malartic consistent with the known systematic watering performed by the mining company.