A spectral library for a semi-arid wetland and its application to studies of wetland degradation using hyperspectral and multispectral data

Abstract

Semi-arid wetland areas in Central Spain are especially sensitive ecosystems and are considered to be one of the most important areas for the migration and wintering of waterfowl in Europe. Many of these wetland areas are saline or sub saline and are subjected to natural (seasonal) as well as human induced changes. Factors causing changes that significantly alter or modify the ecological function of these wetlands are considered to be degradation processes. The use of hyperspectral and multispectral data together with ground spectra and field studies has a great potential for monitoring wetland conditions. In this work spectral and analytical information concerning soil, vegetation and land use, contained in a site specific spectral library, is linked with the spectral characteristics of components from an anthropogenic influenced wetland area in La Mancha Alta. This information forms the basis for determining and selecting end members from hyperspectral data (DAIS 7915), which are then extrapolated to lower spatial and spectral resolution multispectral Landsat ETM+ and TM data. A spectral unmixing is carried out to obtain a multitemporal analysis for evaluating wetland degradation. Results show that the approach is successful in determining rapid surface change due to anthropogenic influences. Spectral unmixing results present an increase of salt-affected soil and a redistribution of saline pasture. This is further supported with a post classification change detection assessment and ground data confirm that principal causes are changes in wetland use together with water regulation of the Cigüela river.

Acknowledgments

The authors acknowledge the support of the UK Natural Environment Research Council Equipment Pool for Field Spectroscopy (NERC EPFS), for the loan of the ASD FieldSpec Pro spectroradiometer used in this research. The authors express their gratitude to the German Aerospace Centre (DLR) for provision with the DAIS 7915 data, collected during the HySens Project.