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A remote-sensing method of mapping soils and surficial lags from a deeply weathered arid region, near Cobar, NSW, Australia

School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia(e-mail: rdehaan@csu.edu.au and G.Taylor@unsw.edu.au)

The work reported here describes the use of hyperspectral imagery for discriminating and mapping the mineralogy of surface materials at a semi-arid site in New South Wales, Australia. Hyperspectral imagery for the Mrangelli test site near Cobar was acquired by the HyMap instrument, a 126-channel, high spectral and spatial resolution airborne scanner. Ground investigations demonstrate that HyMap is able to acquire spectra of 5 m pixels that have a similar spectral resolution to spectra acquired with a field spectrometer. Unmixing of endmembers from calibrated HyMap imagery allowed outcrops of maghemite-rich pisoid lags, lithic lags, ferrolithic lags, metasediments and soils to be discriminated and mapped. The pisoid lag is shown by field and image spectra to be a mixture of hematite/maghemite Fe oxides and kaolinite. Lithic lags show features that resemble mixtures of hematite and illite. Class maps derived from the visible and near-infrared (VISNIR) part of the spectrum delineate terrain elements distinguished by their Fe mineralogy and content. Class maps derived from the shortwave infrared part (SWIR) of the spectrum delineate terrain elements distinguished by their clay mineralogy, content and crystallinity. Unique combinations of VISNIR- and SWIR-derived terrain elements define geomorphic terrains common within the region. It is proposed that maps of lag distribution and the accompanying terrains derived from HyMap imagery could be used to differentiate in-situ from transported materials and therefore aid in the planning of sample locations for soil and lag geochemistry exploration programmes.

KEYWORDS: regolith, hyperspectral, lags, residual, transported