Bathymetry GA 2009 9sec v4

Abstract

This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied.

In 2005 Geoscience Australia and the National Oceans Office undertook a

joint project to produce a consistent, high-quality 9 arc second

(0.0025° or \~250m at the equator) bathymetric grid for Australian waters.

In 2009 there are a number of new datasets that would optimally be

included in the grid to ensure the most up to data is available.

The 2009 bathymetric grid of Australia has been produced to include the

new datasets available, and to provide a grid that fixes issues identified

in the previous version. The revised grid has the same extents as its 2005

counterpart, including the Australian water column jurisdiction lying

between 92° E and 172° E, and 8° S and 60° S. The waters adjacent to the

continent of Australia and Tasmania are included, as are areas surrounding

Macquarie Island, and the Australian Territories of Norfolk Island, Christmas

Island, and Cocos (Keeling) Islands. The area selected does not include

Australia's marine jurisdiction off of the Territory of Heard and McDonald

Islands and the Australian Antarctic Territory.

This report details the datasets and procedures used to produce the 2009

bathymetric grid of Australia. As per the 2005 grid, "the underlying data

from which this grid is derived can only support the 0.0025deciaml degree (dd)

resolution in areas where direct bathymetric observations are sufficiently

dense (e.g. where swath bathymetry data or digitised chart data exist)"

(Webster and Petkovic, 2005). In areas of land the grid is based on the

revised Australian 0.0025dd topography grid, the 0.0025dd NZ topography

grid and the 90m SRTM DEM. In areas where no sounding data are available

(in waters off the Australian shelf), the grid is based on the 2 arc minute

ETOPO satellite derived bathymetry.

The final dataset has been provided in ESRI grid and ER Mapper (ers) formats.

An associated shapefile has been produced so that the user can identify the

input datasets that were used for each part of the final grid.

IMPORTANT INFORMATION

This grid is not suitable for use as an aid to navigation, or to replace any

products produced by the Australian Hydrographic Service. Geoscience Australia

produces the 0.0025dd bathymetric grid of Australia specifically to provide

regional and local broad scale context for scientific and industry projects,

and public education.

The 0.0025dd grid size is, in many regions of this grid, far in excess of the

grid size that is optimal for the data used. In on-shelf areas it may be

possible to produce a higher quality grid. This would be particularly of use

in inshore zones where currently interpolation makes up the majority of data,

and the 0.0025dd grid size means that smaller surveys represent only one or

two pixels in the grid.

There are a number of bathymetric datasets that have not been included in

this grid for numerous reasons. If there are any datasets that are available

and are not in this version, or datasets that could be made available for

subsequent iterations of the bathymetry grid, or for any further comments or

queries, please contact: IDEASRequests@ga.gov.au.

Dataset History

The data came from a variety of systems with differing data densities and levels of accuracy. In the geographic extents 34N - 79S, 90E -180E, GA holds approximately 1400 surveys that collected bathymetric data. For ship-track data the typical spacing of point data along track is 25-200m, the two-dimensional spacing of points covered by swath surveys is of similar order.

The coverage of ship-track surveys is widely variable, such that some points covered by grid lines are many tens of kilometres apart, whereas for swath bathymetry surveys, the areas of coverage are at relatively high density, but of very limited coverage. This product documents the procedures used to construct the bathymetric grid and their associated displays. The input data were derived from a number of sources, were of variable vintages and quality. A number of approaches were required to process, check and edit the data. The availability

of data also varied considerably throughout the region, effectively restricting the maximum useful resolution of the grid in areas where no soundings exist, to

that of the satellite predicted bathymetry that was used as infill.

These data, together with predicted bathymetry from satellite altimetry, have been brought together into a single data and processing system to allow the routine creation of grids with a range of specifications, from which grids and images can be created.

Dataset Citation

Geoscience Australia (2014) Bathymetry GA 2009 9sec v4. Bioregional Assessment Source Dataset. Viewed 22 June 2018, http://data.bioregionalassessments.gov.au/dataset/60fb8bf5-b97d-49c9-b7fb-e7d594d2c75b.