The Creation of High Resolution Bathymetry Grids for Cocos (Keeling) Island

The grids are derived from data in Geoscience Australia databases and recent sources which will eventually be entered into those databases. Satellite derived bathymetry was used in shallow waters. Two swath datasets acquired between 2003 and 2008 were used. Both surveys supply extensive regional coverage. A high quality coastline, as well as topography data of Cocos and its islands were obtained from the GEMD GIS. Eleven singlebeam surveys from the GA MARDAT database. These data range in vintage from 1965 to 2000 and were edited to remove suspect datapoints, but were left uncorrected with regards speed of sound issues. Chart data from the AHS was used in both deep and shallow water. One singlebeam survey commissioned by DoTaRS that was previously unknown to GA was used.Cocos (Keeling) Island is located approximately 3,685km almost due west of Darwin. It is a mid-ocean atoll with a coral reef, and a very shallow (1 - 20 m) shelf surrounds the island. Bathymetry data are required in this area to help identify major seabed processes and habitats. The data are also required to enable modelling of tsunami as they interact with the shelf around the island and the coast. This report describes the methodology employed in creating detailed bathymetry data grids of the Cocos (Keeling) Island region. It covers data collection, quality control and gridding. Descriptions are provided of each dataset employed, the methods used to integrate the different datasets and the attributes of the new bathymetry models. Four new bathymetry grids are presented, including grids that integrate bathymetry with the island's topography