Hyperspectral linear mixing based on in situ measurements in a coral reef environment

With the benthic complexity common on a coral reef, there will always be subpixel mixing given the spatial resolution of contemporary satellite imagery. It therefore becomes important to determine how spectral components of a pixel combine to result in one integrated pixel value. To address this issue, pure endmember high spectral resolution measurements were taken in Buck Island Marine Park, off St. Croix, U.S. Virgin Islands. Linear spectral mixing was used with these endmember spectra (coral, sand, grass, bleached coral, and benthic algae) to examine the integrated pixel signals. Results indicate that when the sand component of the mixed spectra is only 25%, there is a notable increase in magnitude of reflectance. Cluster analyses of end member spectra and mixed spectra indicate that a relatively small sand component within a mixed pixel will effectively dominate the pixel's spectral signal. The spectral signal of a pixel with only 25% sand cover lacks similarity to other endmembers present, retaining spectral characteristics specific to sand, with significant implications for image analysis.