Authors: Beaman, R. J.
Publication: Ecotone. Cairns and Far North Environment Centre, Cairns, Australia, 36(4), 10.
It is often said, we know more about the surface of Mars than we do about Earth’s oceans. While all of Mars has now been mapped using satellite technology, less than 15% of the Earth’s oceans deeper than about 200 metres have been mapped using modern bathymetric surveying techniques.
Beside the difficulty of mapping the deep oceans, another major challenge is to sufficiently map the reefs and hazards of the shallower continental shelves to enable the safe transit of shipping traffic and the protection and management of sensitive marine areas, issues of vital importance to Australia as a maritime nation.
In the Great Barrier Reef Marine Park, with over 9000 ship voyages in 2012-13, the task of surveying the maze of reefs that make up the largest coral ecosystem on Earth, fell to the Australian Hydrographic Service (AHS) and the fleet of Royal Australian Navy hydrographic survey vessels and aircraft, mostly based in Cairns.
To overcome the problem of traditional vessel surveys over dangerous reefs, an aircraft-mounted Laser Airborne Depth Sounder (LADS) uses red and green LiDAR technology to rapidly scan the seafloor to depths of about 50 metres, generating a dense grid of depth data points. The bathymetry data are then used by the AHS to revise the nautical charts used by mariners.
Several years ago, we approached the AHS for the raw LiDAR data from the northern Great Barrier Reef to develop 3D depth models for marine geology research. The results were simply astounding. Aside from the shallow coral reefs revealed by their detailed 3D shapes of reef flats, lagoons and pinnacles, it was the deeper inter-reef seafloor behind the familiar coral reefs that amazed us.
The new high-resolution seafloor data revealed great fields of unusual donut-shaped circular mounds, each 200-300 metres across and up to 10 metres deep at the centre. These geological structures have been known about in the northern Great Barrier Reef since the 1970s and ‘80s, but never before has the true nature of their shape, size and vast scale been revealed.