Mapping Soil indicators of Dryland Salinity Using Hymap Hyperspectral Imagery

要旨

Salinisation is a worldwide problem and the cause of major soil degradation in many parts of Australia. The objective of this research is to evaluate the use of hyperspectral imagery for mapping the spatial distribution of soil indicators of dryland salinisation at Dicks Creek, a site in the Yass River catchment of New South Wales. Strategies for mapping image-derived terrain-type spectra from HyMap imagery are assessed and a mixture-tuned matched filter approach adopted. Terrains of exposed soils, weathered rock, colluvium, clay and lag materials occurring around saline scalds can be differentiated on the basis of iron and clay-related spectral features. The colluvium and clay profiles were identified as the most saline, indicating that these particular units are crucial to accurately mapping dryland salinisation. No diagnostic evaporite minerals can be recognised but the high spectral resolution of HyMap allows colluvium and clay soil outcrops to be differentiated from one another. Mineral analysis using field spectrometry and X-Ray Diffraction (XRD) techniques confirm the likely presence of an aeolian, smectite clay component. The soils within the region are considered to be combinations of the normal weathering products of the basement rocks and a salt-enhanced windblown dust that accumulated during cold and arid glacial periods. The soils have subsequently been redistributed from the valley sides to the valley floors as debris-flows. Integration of the digital elevation model and hyperspectral data is useful for visualising the spectral and spatial relationships of the key terrain types and for mapping areas affected by dryland salinisation.