MAPPING THE SPECTRAL AND SPATIAL CHARACTERISTICS OF MOUND SPRING WETLAND VEGETATION IN SOUTH AUSTRALIA: A NOVEL SPECTRALLY SEGMENTED PCA APPROACH

摘要

The Australian Great Artesian Basin mound springs are unique wetland ecosystems of great ecological, scientific, economic importance and culturally significant for indigenous Australians. In recent decades the ecologial sustainability of the springs has become uncertain as demands for this precious water resource increase. Research methods are being developed using hyperspectral remote sensing for mapping and monitoring the sensitivity of spring vegetation to mining and pastoral water allocations and land use. The aim of this paper is to evaluate the use of Spectrally Segmented Principal Component Analysis (SSPCA) with airborne hyperspectral data to map the extent, distribution and diversity of mound spring permanent wetland vegetation. HyMap airborne hyperspectral imagery was acquired in March 2009 coinciding with a field campaign of spectroradiometry measurements and botanical survey. SSPCA was applied to NDVI masked vegetation portions of the HyMap imagery with wavelength regions spectrally segmented for VIS-NIR, 450-1,350 nm, SWIR1, 1,400-1,800 nm, and SWIR2, 1,950-2,480 nm. VIS-NIR PCs 2, 3 and 9 identified key vegetation discrimination wavelength features, i.e., green peak at 555 nm, chlorophyll absorption at 685 nm, and VIS-NIR and red-edge contrasts. SWIR1 PC 3 mapped the invasive species Phragmites australis, with notable loadings at 1,450, 1,645-1,715, 1,815, and 1,825 nm associated with water, lignin, and cellulose absorptions, respectively. PC 3 mapped Phragmites successfully, coinciding with Phragmites in survey field plots verified with 30 cm digital aerial photography. The results suggest that SSPCA is capable of revealing considerable spectral variation within spring wetland vegetation, providing a good basis for discriminating communities.