Coral reefs: a multi-scale approach to monitoring their composition and dynamics

Effective use of remotely sensed data requires a conceptual understanding or model of the attributes of that environment that control the reflection, absorption and transmission of electromagnetic radiation (EMR). This model needs to be developed at a number of spatial scales and for imagery acquired from various regions of the electromagnetic spectrum. Coral reefs have, as yet, not been studied in this way. A complicating factor is that spatial variations of water depth and water quality prevent normalisation of image data to allow accurate mapping, estimation of biophysical properties and change detection. Another factor is the geometry and scale of reef feature variation, especially in relation to the vertical orientation and location of photosynthetic and productive components. The aim of this paper is to present a conceptual model for extracting multi-temporal biophysical information from remotely sensed data of coral reefs. The model is applicable from the scale of micro-algae and polyps, to individual coral heads, reefs and reef ecosystems, and is intended to provide a basis for ´scaling-up´ fine scale measurements to cover larger areas and longer time periods. Model development and testing involved reviews of relevant literature coupled with field spectrometer and pulse amplitude modulated (PAM) fluorometer data, airborne multispectral and hyperspectral image data, and satellite multispectral data from the Great Barrier Reef (GBR), Australia