The application and potential of remote sensing in the Great Barrier Reef

Water movements in the form of currents, internal waves, eddies and moving boundaries between water masses (oceanic fronts) are primary elements driving the Great Barrier Reef (GBR) system. The physical and chemical characteristics of the water column, as major factors in the short and long term development of the GBR biological system, subdivide the physical system into its component water masses. The material carried by the physical system consists of biota and suspended solids of natural (eg phytoplankton) and man induced (eg pollution) composition. Existing remote sensing devices provide an opportunity to gather valuable data on these dynamic physical and biological systems, and the complex of inter-reef communications they provide. Remote sensing by Landsat is already established as a tool for the establishment of a basic fixed-reef data base for the GBR. This (static) data base is effective for current inventory and many planning needs. However, future management within the GBR system must use an information base which does not neglect the essentially dynamic interdependency between the reef environments and the communities which exist within and between them. In the dynamic GBR physical system, events at whole GBR level may be as significant as events at within reef level. The problem of encompassing the wide range of time and space scales involved is one which only aircraft and satellite remote sensing in combination with ship and reef based studies can solve. This report addresses the way in which remote sensing opportunities exist to provide such integration and identifies a program of research and development which may achieve it

Three-dimensional mapping of light transmittance and foliage distribution using lidar

The horizontal and vertical distributions of light transmittance were evaluated as a function of foliage distribution using lidar (light detection and ranging) observations for a sugar maple (Acer saccharum) stand in the Turkey Lakes Watershed. Along the vertical profile of vegetation, horizontal slices of probability of light transmittance were derived from an Optech ALTM 1225 instrument's return pulses (two discrete, 15-cm diameter returns) using indicator kriging. These predictions were compared with (i) below canopy (1-cm spatial resolution) transect measurements of the fraction of photosynthetically active radiation (FPAR) and (ii) measurements of tree height. A first-order trend was initially removed from the lidar returns. The vertical distribution of vegetation height was then sliced into nine percentiles and indicator variograms were fitted to them. Variogram parameters were found to vary as a function of foliage height above ground. In this paper, we show that the relationship between ground measurements of FPAR and kriged estimates of vegetation cover becomes stronger and tighter at coarser spatial resolutions. Three-dimensional maps of foliage distribution were computed as stacks of the percentile probability surfaces. These probability surfaces showed correspondence with individual tree-based observations and provided a much more detailed characterization of quasi-continuous foliage distribution. These results suggest that discrete-return lidar provides a promising technology to capture variations of foliage characteristics in forests to support the development of functional linkages between biophysical and ecological studies