Bathymetric grid of Macquarie Island Region (2004)
Entry ID:
AADC_Macquarie_bathy_grid
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Summary
Abstract:
This metadata record is a modified child record of an original parent record originating from custodians of data associated with Geoscience Australia (The identifier of the parent record is ANZCW0703006701, and can be found on the Australian Spatial Data Directory website - see the URL given below). A bathymetric grid of the Macquarie Island Region (Longitudes 151 E and 167 E, Latitudes 48 S and ... 62 S) is produced. In doing so, the individual datasets used have been closely examined and any deficiencies noted for further follow up or have been rectified immediately and the changes documented. These datasets include modern multibeam data, coastline data obtained from georeferenced SPOT imagery, hydrographic quality data, echosounder data from research and fishing vessels and satellite derived bathymetric data. A hierarchical system was employed whereby the best and most extensive datasets were gridded first and applied as a mask to the next best dataset. A new masking grid would be formed from these datasets to pass non-overlapping data in the next best dataset. This procedure was employed until finally the satellite data were masked. All the various levels of masked data were then brought together by the gridding algorithm (Intrepid and Desmond Fitzgerald Associates) and an ERMapper format grid produced. A grid cell size of 0.00225 (nominal 250m) was used with many iterations of minimum curvature gridding and several passes of smoothing. The final grid is available in ArcInfo interchange, ArcInfo ascii and xyz text formats. A detailed report of the work completed is also available.
Related URL
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Description:
Details on how to access the bathymetric data as an ArcInfo interchange file
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Geographic Coverage
(Click for Interactive Map)
Spatial coordinates
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N: -48.0
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S: -62.0
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E: 167.0
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W: 151.0
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Temporal Coverage
Start Date:
2004-03-01
Stop Date:
2004-06-01
Start Date:
1994-01-01
Stop Date:
2003-12-31
Quality
Lineage: The grid is derived from data in Geoscience Australia databases and recent sources which will eventually be entered into those databases. Eight swath datasets acquired between 1994 and 2003 were used. Two of the surveys supply extensive areal coverage, whilst the others are basically multibeam transits of the area. Detailed hydrographic data (including a 1999 ... LADS dataset near the northern tip of Macquarie Island) exists around the island. A high quality coastline of Macquarie Island from the National Mapping Division of G.A. (1994) and a coastline of the New Zealand islands obtained from the NOAA website were used . High quality bathymetric data (post 1997) from Austral Fisheries Pty Ltd were made available via the AAD. Twenty-five surveys from the G.A. MARDAT database. These data range in vintage from 1965 to 1998 and were edited to remove suspect datapoints, but were left uncorrected with regards speed of sound issues. All available data in the area from the AAD voyages in the region. Extensive editing and a weighting scheme were employed to discriminate between closely spaced data of varying vintages. Other trackline data on NGDC and CSIRO websites that were not in MARDAT were also utilised. Satellite derived bathymetry from the SIO website was used to infill areas that had no higher quality observations within a nominal 10 kilometres. Positional accuracy: The grid incorporates data from surveys acquired since 1965. 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 satellite data to provide infill between sparse ship track data of lower positional and bathymetric accuracy. The grid cell size is 0.00225 (nominal 250m). If displayed at 300dpi, nominal scale is 1:3,000,000 giving a plot size of (60cm x 53 cm) 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. Some transit swath data also have speed of sound corrections applied and are assumed to be highly accurate. Other transit swath surveys have utilized a nominal speed of sound of 1500 m/s and are not as accurate (problems were encountered trying to apply correction). Most other data assume a nominal speed of sound of 1500 m/s, although some 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. Some transit swath data also have speed of sound corrections applied and are assumed to be highly accurate. Other transit swath surveys have utilized a nominal speed of sound of 1500 m/s and are not as accurate (problems were encountered trying to apply correction). Most other data assume a nominal speed of sound of 1500 m/s, although some have had corrections applied. 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 in a regional sense only. 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 were gridded first and applied as a mask to the next best dataset. A new masking grid would be formed from these datasets to pass non-overlapping data in the next best dataset. This procedure was employed until finally the satellite data were masked. All the various levels of masked data were then brought together by the gridding algorithm (Intrepid and Desmond Fitzgerald Associates) and an ERMapper format grid produced. Completeness: All of the known, available data (to 2004) were used in the production of the grid. The only data known to not be included are some surveys within the New Zealand EEZ, but these proved impossible to obtain. The G.A. databases which underpin this grid will be updated as new surveys are completed and older surveys have corrections applied to them. It is planned to be somewhat proactive and asking regular visitors to the region to vary their transits slightly to extend the coverage over time. A data density grid 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. 
Access Constraints
Data are stored in digital format - ER Mapper raster dataset Geographic WGS84. Data are available in digital format - ArcInfo interchange Geographic WGS84 ArcInfo ascii Geographic WGS84 text file in x,y,z format Geographic WGS84. Australian Antarctic Division staff are able to access these data, and a copy of the report, from the URLs given below. Note that the bathymetry data are not available for online download as they are too large - see the URLs below, and contact the Australian Antarctic Data Centre for access.
Use Constraints
This data set conforms to the PICCCBY Attribution License (http://creativecommons.org/licenses/by/3.0/). When using these data, Geoscience Australia must be acknowledged. If the data were obtained from the Australian Antarctic Data Centre, that must also be acknowledged. Please follow instructions listed in the citation reference provided at the URL below when using these data.
Data Set Progress
COMPLETE
Distribution
Distribution Media:
FTP or CD
Distribution Size:
223 MB
Distribution Format:
ArcInfo interchange file
Fees:
free
Distribution Media:
FTP or CD
Distribution Size:
213 Mb
Distribution Format:
ArcInfo ascii file
Fees:
free
Distribution Media:
FTP or CD
Distribution Size:
434 Mb
Distribution Format:
x,y,z text file
Fees:
free
Distribution Media:
HTTP
Distribution Size:
2 MB
Distribution Format:
pdf
Fees:
free
Personnel
Role:
INVESTIGATOR
Role:
TECHNICAL CONTACT
Email:
mike.sexton at ga.gov.au
Contact Address:
Geoscience Australia
GPO Box 378
City:
Canberra
Province or State:
Australian Capital Territory
Postal Code:
2601
Country:
Australia
Role:
INVESTIGATOR
Role:
TECHNICAL CONTACT
Email:
morgan.tully at ga.gov.au
Contact Address:
Geoscience Australia
GPO Box 378
City:
Canberra
Province or State:
Australian Capital Territory
Postal Code:
2601
Country:
Australia
Role:
TECHNICAL CONTACT
Phone:
+61 3 6232 3528
Fax:
+61 3 6232 3351
Email:
mapping at aad.gov.au
Contact Address:
Australian Antarctic Division
203 Channel Highway
City:
Kingston
Province or State:
Tasmania
Postal Code:
7050
Country:
Australia
Role:
DIF AUTHOR
Phone:
+61 3 6232 3244
Fax:
+61 3 6232 3351
Email:
dave.connell at aad.gov.au
Contact Address:
Australian Antarctic Division
203 Channel Highway
City:
Kingston
Province or State:
Tasmania
Postal Code:
7050
Country:
Australia
Creation and Review Dates
DIF Creation Date:
2007-02-20
Last DIF Revision Date:
2009-05-11
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