Process-based Mapping Using Spectral Indicators in an Image Template Matching Approach

In geologic imaging spectroscopy studies, typical end products are often mineral maps. These maps are usually ambiguous and form a limited method of representing geological information that is potentially contained in spectroscopic images. This situation can be improved by mapping the spatial configuration of the effects of geological processes instead of the solely individual minerals in a non-spatial context. This so-called process-based mapping opens the way for a truly contextual mapping approach since the spectrally detectable expressions of processes occur in specific spatial arrangements. The contextual approach will solve the ambiguity problem occurring in mineral maps and will facilitate targeting of geologic processes. End products of this approach are not mineral maps but a map of the geological process. A typical geologic process that is suitable for mapping using airborne imaging spectroscopy is submarine hydrothermal fluid circulation. Fluid pathways in fossil hydrothermal systems mark the start, the course, and the end fluid circulation from sites of recharge to sites of discharge. Boundaries between alteration facies along fluid pathways are zones where physico-chemical conditions change and these are required for reconstruction of the affects of hydrothermal processes and fluid pathways. In this paper, we demonstrate that we are able to map the various boundary zones in a fossil hydrothermal system using HyMap hyperspectral imagery in a contextual image processing approach using the RTM algorithm. The boundary zones between specific neighboring alteration assemblages were identified from spectral indicator images derived form airborne HyMap data. The supervised detection of boundary zones using this method is unbiased and selective to user-defined settings. Results in this study are useful for studies on hydrothermal systems and in particular in the search for early life on earth and other planets and in the exploration for hydrothermally formed mineralizations.