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

Note: This metadata describes the dataset in accordance with the ANZLIC (Australia New Zealand Land Information Council) Core Metadata Guidelines Version 2.


Dataset citation

ANZLIC unique identifier: ANZCW0703013943

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


Custodian

Custodian: Geoscience Australia

Jurisdiction: Australia


Description

Abstract:

Cocos (Keeling) Island is located approximately 3,685 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.

Four new bathymetry grids have been created, including grids that integrate bathymetry with the island's topography.

ANZLIC search words:

  • GEOSCIENCES Geomorphology
  • GEOSCIENCES Geophysics
  • MARINE
  • MARINE Reefs
  • OCEANOGRAPHY Physical

Spatial domain:

locality map

Geographic extent name: COCOS (KEELING) ISLAND - COI - External Territories - Australia

Geographic extent polygon: 95.5 -11.0, 98.0 -11.0, 98.0 -13.0, 95.5 -13.0, 95.5 -11.0,

Note: The format for each Geographic extent name is: Name - Identifier - Category - Jurisdiction (as appropriate) See GEN Register

Geographic bounding box:
North bounding latitude: -11 °
South bounding latitude: -13 °
East bounding longitude: 98 °
West bounding longitude: 95.5 °

Data currency

Beginning date: 2009-07-01

Ending date: 2010-06-30


Dataset status

Progress: Complete

Maintenance and update frequency: Not Known


Access

Stored data format:
DIGITAL - ers ER Mapper raster dataset ER Mapper Geographic WGS84
DIGITAL - XYZ ascii XYZ ascii grid ArcGIS Geographic WGS84
Available format type:
DIGITAL - XYZ ascii XYZ ascii grid ArcGIS Geographic WGS84
DIGITAL - ers ER Mapper raster dataset ER Mapper Geographic WGS84

Access constraints:

Only the 250 m grid is publicaly available.

Free Data Download

Data quality

Lineage:

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.

Positional accuracy:

The grid incorporates data from surveys acquired since 1959. Modern surveys which used GPS have a positional accuracy of 5 - 30 m depending on several factors, while earlier surveys which used dead reckoning and Transit satellite fixes had positions accurate to 50- 2000 m depending upon the water depth and strength of currents. These surveys overlap in an irregular distribution and the more extensive, higher quality swath datasets were used to mask data of lower quality and extent. Effectively there are two regions in the grid. One covered by multibeam data of high positional and bathymetric accuracy and the other heavily reliant on chart data and singlebeam surveys which are of lower positional and bathymetric accuracy. The grid cell sizes are 0.00225 deg (nominal 250m), 0.0009 deg (nominal 100m), 0.00045 deg (nominal 50m) and 0.00009 deg (nominal 10m).

Attribute accuracy:

The attribute accuracy varies depending upon the predominant data source in an area. Where modern, high quality swath bathymetric data that form an areal coverage exists, overlapping swaths and speed of sound corrections show that the data are quite accurate. For a significant portion of the region, predicted bathymetry from satellite data are the only source of data and the accuracy of these data are known to be good. No attempts have been made to compare bathymetry from high quality datasets to that which would be obtained from lesser data sets, although all the data exist to perform such a task.

Logical Consistency:

Each of the input datasets was examined in detail and edited where necessary. Areas of poor navigation and obviously bad bathymetry were discarded. A hierarchical system was employed whereby the best and most extensive datasets replaced data of lesser datasets. All the various datasets were then brought together by the gridding algorithm (Intrepid : Desmond Fitzgerald Associates) and an ERMapper format grid produced.

Completeness:

All of the known, available data (to 2010) were used in the production of the grids. The GA databases which underpin this grid will be updated as new surveys are completed and older surveys have corrections applied to them. A data density map was produced as a means of assessing the completeness of coverage and it could possibly be used as a variably opaque overlay of the bathymetric grid to highlight good quality areas and darken lesser quality areas.


Contact information

Contact organisation: Commonwealth of Australia (Geoscience Australia) (GA)
Contact position: Manager Client Services
Mail address: Cnr Jerrabomberra Ave and Hindmarsh Dr
Mail address: GPO Box 378
Locality: Canberra
State: ACT
Country: Australia
Postcode: 2601
Telephone: 02 6249 9966
Facsimile: 02 6249 9960
Electronic mail address: sales@ga.gov.au

Metadata information

Metadata date: 2013-03-08


Additional metadata

Metadata reference XHTML: http://www.ga.gov.au/meta/ANZCW0703013943.html

Metadata reference XML: http://www.ga.gov.au/meta/ANZCW0703013943.xml

Mleczko, R., and Sagar, S., 2010. High Resolution Bathymetry Grids for Cocos (Keeling) Island. Geoscience Australia Record 2010/38.

Authors:Mleczko, R. Sagar, S.
SPATIAL INFORMATION FOR THE NATION