Invited Speakers

John Hedley received his BSc in Zoology from the University of Newcastle in 1995 and was awarded a PhD at Exeter University in 2004 for his work on new methods and modelling approaches for remote sensing of coral reefs. John is currently funded by the UKs Natural Environmental Research Council (NERC) as a Research Fellow at Exeter University and is also a member of the Remote Sensing Working Group of the World Bank/GEF Targeted Research Program for Coral Reefs. John's primary research interest is radiative modelling in shallow water ecosystems, in particular, three-dimensional canopy modeling of coral reefs. Applications of his work have two distinct strands 1) to establish the fundamental limits of what can be achieved in remote sensing of coral reefs and to produce optimal inversion algorithms and objective-orientated sensor designs, and 2) to investigate the interaction between the morphology of coral reef organisms, light and photobiology, with one aim being to understand the role of light-stress as causal factor in coral bleaching (loss of zooxanthellae) and mortality.

Abstract

Many shallow water ecosystems such as coral reefs or kelp forests exhibit complex three-dimensional structures within the water column. In addition, the water surface typically contains wave structure across a range of scales from mm's to meters. Taken as a whole, the water column and benthos therefore comprise a complex three-dimensional canopy that is an extremely challenging environment for radiative transfer modelling of visible light. Plane-parallel modelling approaches cannot be applied where vertical structure in the benthos can approach the height of the water column itself, whereas Monte-Carlo techniques rapidly become computationally infeasible due to the potential for multiple scattering between natural structures, the water column and surface. In this presentation I will describe a solution method capable of handling arbitrary arrangements of surfaces and scattering media in three-dimensions and its application to shallow water environments. The method is similar to radiosity methods developed for computer graphics applications, but has been substantially augmented to include directional scattering from surfaces and volumetric media, and to provide comparable accuracy to existing plane parallel methods. Applications of the model include canopy modelling for remote sensing and photobiology, in which the modelled radiance distribution includes processes such as multiple scattering and shading within benthic structures, wave-focusing on substrates and spatial patterns of above-surface sun-glint.