Great Barrier Reef Bathymetry. Image Credit: EOMAP GmbH & Co. KG (2013).
Taken collectively, the corals and other life forms that make up the Great Barrier Reef of Australia comprise one of the largest living structures on Earth. This natural wonder provides habitat for a teeming multitude of species and stands as a protective break for a portion of Australia’s coastline. It also has long sparked the curiosity of explorers, divers, and marine biologists and in recent years has drawn attention in a less cheerful light as a potential casualty of rising ocean temperatures. In spite of its allure, however, the Great Barrier Reef had never been comprehensively mapped until now.
“Paul Reef and Surrounding.” Image Credit: EOMAP GmbH & Co. KG (2013).
On Nov. 20, German and Australian scientists announced the successful creation of high-resolution, digital maps for the entire of the Great Barrier Reef. These maps were created using satellite measurements to derive sea floor reflectance and shallow water bathymetry, or submarine topography, of the region.
The mapping project was enabled by a German-based company known as EOMAP (Earth Observations and Mapping), which focuses on aquatic remote sensing, in partnership with the Cooperative Research Centre for Spatial Information, and the Centre for Spatial Environmental Research of the University of Queensland and James Cook University in Australia.
Difficulty mapping the Great Barrier Reef arises from its size and nature. It is in fact not one reef, but a series of reefs. It is so large that it stretches for more than a thousand miles from end-to-end and can be seen from space. Previous to this project, modern digital surveys had only been completed for portions of the reef. Remote locations, combined with the navigational danger of sharp edges in shallow water, had posed challenges to surveying by traditional shop-based methods. It is estimated that over half of the topography of shallow water sections of the Great Barrier Reef had remained uncharted.
To avoid challenges of surveying these remote or perilous sites, EOMAP made use of images taken by the Landsat 7 and Landsat 8 satellites. Satellite images and data were analyzed to complete their charts of the Great Barrier Reef, primarily making use of satellite derived bathymetry.
Satellite derived bathymetry (SDB) works by measuring the amount of sunlight reflected from the sea floor. The readings from these sensors can be plugged into algorithms that calculate the depth of the water column. Sunlight reflectance is only useful up to depths of approximately 30 meters, but these shallow depths are the most difficult to measure by ship-based surveys, and for areas where the water column depth is greater than 30 meters, surveys can be taken by ships using traditional methods.
Gathering the data is only the beginning of the process. Pre-processing involves selecting data and organizing them into identified areas of interests.
Images must then be processed to correct for cloud cover, sun glare, or and other conditions that might impact measurements.åÊ The data are then processed by EOMAP’s Modular Inversion Processor, which retrieves sea floor reflectance and water column depth. Post processing includes making corrections based on tides and turbidity.
Schematic illustrating the path of the sunlight signal, interacting with the atmosphere, water column and seafloor, and finally being measured by a space-borne or airborne sensor. Image Credit: Centre for Spatial Environmental Research, University of Queensland.
Matching the scope of its subject, the Great Barrier Reef, the scope of the EOMAP project is one of the largest in Australia’s history.
The water depth maps that have been created using this process are available online in 3D format, and there are maps with 30-meter horizontal resolution for more than 350,000 square kilometers of the reef. The project aims to offer options for both detailed data of specific locations and a comprehensive overall picture of this vast ecosystem. åÊProject participants hope the information provided by these maps will lead to deeper understanding of the nature and function of the Great Barrier Reef, thereby assisting in the preservation of a delicate and iconic hot spot of biodiversity.
Individuals interested in viewing the maps may purchase high-resolution versions on the EOMAP website. Requests also can be made to receive sample high-resolution or lower-resolution (500 meter) maps free of charge.åÊ A summary of the project and its assessment by Dr. Robin Beaman of James Cook University and Dr. Chris Roelfsema of the University of Queensland can be found at EOMAP.