The 2005 coral-bleaching event Roatan (Honduras): Use of pseudo-invariant features (PIFs) in satellite assessments

Radiometric normalisation is a necessary precursor to detecting coral-bleaching from a time series of imagery. Using IKONOS and QuickBird, the pseudo-invariant-feature (PIF) approach was assessed, and found that small subsets and land-based PIFs lead to erroneous normalisation. In comparison, favourable results were achieved by using benthic sand and deep water subsets, coupled to a sun-deglint process. Furthermore, it was found the more traditional strategy of 'difference imaging' to be compromised by slight spatial alignment errors between image sets. Our alternative approach, based on spectral radiance, ably discerned significant brightening of areas of seafloor populated by dense stands of Acropora, corroborating the Occurrence of a documented bleaching event.