Mapping of soil surface crusts using airborne hyperspectral HyMap imagery in a Mediterranean environment

Abstract. Soil surface crusting is a common but unfavorable process in Mediterranean environments. Soil surface crusts hamper infiltration of water into the soil and stimulate surface runoff, erosion and flooding downstream. Furthermore, crusts hinder germination of seeds and settlement of plants. Surface crusts develop within minutes during high intensity rainfall typical for arid and semi-arid environments. The raindrops destroy the soil aggregates and the aggregates disintegrate into the basic particles clay, silt and sand. Crusts are formed at the surface by compaction or by infilling of the inter-aggregate pore space. The objective of this study was to determine the spectral and physical properties of surface crusts in the field and to investigate the possibilities of hyperspectral airborne imagery to map soil crusts and to identify crusts types. Results show that the differences in some physical properties between crusted and non-crusted surfaces are significant while others show only marginal variation. Infiltration capacity is largely reduced by crusting. Spectral differences are small. Crusted versus non-crusted spectra differ mainly in albedo values (8 to 40%). No consistent changes are found in absorption features in the spectra of crusts and non-crusted surfaces. Some of the crusts show stronger absorption features in the clay mineral absorption bands at 2200nm. Spectral feature fitting and linear spectral unmixing algorithms were applied to HyMap images to evaluate the mapping of surface crusts. The presence of crusts could be mapped for fallow, agricultural lots but in case of natural badland areas the spectral response of the fragmented landscape was too complex to map the presence of crusts