From 1 - 10 / 501
  • The definition of Australia?s marine jurisdiction, under the 1982 United Nations Convention on the Law of the Sea (LOS), may need to take into account the location of the 2500m seafloor contour. A large amount of water depth data from a variety of sources have been used to produce bathymetric grids and contours around the Australian region by the LOS Study Group at Geoscience Australia. It is well known that the data are far from perfect, containing problems in depth soundings as well as navigation. The LOS Group wished to determine a quantitative measure for the accuracy of the data they have used. This study took the data used in the Naturaliste Plateau area and determined the intersection points of all the survey tracks. From this it computed interpolated water depths at the intersections and calculated mistie values between the intersecting surveys. In all 12411 intersections were found. Not all were useable, mainly due to the long intervals between soundings. Some surveys contained numerous intersections in very shallow water (~ 40 m) with excellent mistie statistics (+/- 1 m), but it was felt that these could unfairly bias the derived statistics. Taking these considerations into account reduced the number of intersecting points and mistie values that went into the statistical analysis to 5606. The procedures and programs employed in this report can easily be extended to all the other areas investigated by the LOS Group. This will be done in due course, with a future report summarising the statistics for each of the LOS study areas and making recommendations for the improvement of the bathymetric data held by Geoscience Australia.

  • This record is a report of the operations carried out during Geoscience Australia Survey 229 off the Australian Antarctic Territory from January-April 2002. The survey acquired deep-seismic and potential field data along 8600 km of profiles as a part of the Australian Antarctic and Southern Ocean Profiling Project.

  • This Record contains a shipboard interpretation of the data acquired on Geoscience Australia Survey 229 off the Australian Antarctic Territory from January-April 2002. The survey acquired deep-seismic and potential field data along 8600 km of profiles as part of the Australian Antarctic and Southern Profiling Project.

  • The Eltanin Geophysical datasets are a major resource for examining the geology of the Southern Ocean. Unfortunately, the data have been loaded into Geoscience Australia databases in a rather piecemeal fashion over two decades leading to a number of inconsistencies and duplication. This report documents what Geoscience Australia?s data holdings are, the nature of the problems found and their solution. The report hopes to provide a level of confidence to previous and future users of the data by showing that the status of the data is well understood and documented. This report is intended to be the first of a series of reports examing the various datasets that make up the Geoscience Australia marine, geophysical database OZMARII.

  • The Australian National Marine Data Group was formed by the Heads of Marine Agencies (HOMA) to promote improved interchange of marine data in Australia. The ANMDG held a workshop of practitioners in May 2002 with the intention of identifying major areas of interest and tasks for working groups to address in order to make progress with development of marine data interchange in Australia. This Proceedings CD contains the presentations by speakers in the form of PowerPoint slides and a few Acrobat documents. It was distributed to participants in the workshop.

  • Flythrough movie showing the bathymetry of the continental shelf within the Oceanic Shoals Commonwealth Marine Reserve (Timor Sea), highlighting carbonate banks and pinnacles as benthic habitats. The bathymetric image is derived from multibeam sonar collected in 2012 using a 300 kHz Simrad EM3002 system on RV Solander and gridded at 2 m resolution. The Oceanic Shoals Reserve is a study site for the Marine Biodiversity Research Hub, funded through the National Environmental Research Program. Survey work was carried out as a collaboration between Geoscience Australia, the Australian Institute of Marine Science and University of Western Australia. Further information is provided in GA Record 2013/38.

  • In the past two decades, multibeam sonar systems have become the preferred seabed mapping tool. Many users have assumed that multibeam bathymetry data is highly accurate in spatial position. In reality, both vertical and horizontal uncertainties exist in every data point. These uncertainties are often represented as one single measure of Total Propagated Uncertainty (TPU). TPU is important to understand because it affects the quality of products generated from multibeam bathymetry data. To account for the magnitude and spatial distribution of this influence, an objective uncertainty analysis is required. Randomisation is the key process in such an uncertainty analysis. This study compared two randomisation methods, restricted spatial randomness (RSR) and complete spatial randomness (CSR), in an uncertainty analysis of a slope gradient dataset derived from multibeam bathymetry data. CSR regards data error in every grid cell as independent and assumes that the data error varies within a known statistical distribution without any neighbourhood effect. RSR assumes spatial structure and thus spatial auto-correlation in the data. We present a case study from a survey of the Oceanic Shoals Commonwealth Marine Reserve in the Timor Sea, conducted in 2012 by the Marine Biodiversity Hub through the Australian Government National Environmental Research Program. The survey area is characterised by steep-sided carbonate banks and terraces with abrupt breaks in slope of limited spatial extent. As habitats, the carbonate banks and terraces are important because they provide hardground for diverse epibenthic assemblages of sponges and corals, with their steep sides marking the environmental transition to deeper water, soft sediment habitats. In this analysis, the data errors in the multibeam bathymetry data were assumed to follow a Gaussian distribution with a mean of zero and a standard deviation represented by the TPU. The CSR and RSR methods were each implemented using a Monte Carlo procedure with 500 iterations. After about 300 iterations, the Monte Carlo procedure converged for both methods. Results for the study area are compared against pre-processed slope data (Figure 1a). The averaged slope gradient from the CSR method is 4.5 degree greater than the original slope layer, whereas for the RSR method this value is 0.03 degree. Moreover, the slope layer from the CSR method resolves noticeably less detail than the original slope layer and is an over-simplification of the true bathymetry (Figure 1b). In contrast, the RSR method maintained the spatial pattern and detail observed in the original slope layer (Figure 1c). This study demonstrates that although the uncertainty in multibeam bathymetry data should not be ignored, its impact on the subsequent derivative analysis may be limited. The selection of appropriate randomisation method is important for the uncertainty analysis. When the data errors exhibit spatial structure, we recommend using the RSR method.

  • As part of Geoscience Australia's Southwest Margin Project, two major marine surveys were undertaken (from October 2008 to February 2009) to investigate the resource potential of deep-water frontier areas on the southwest Australian continental margin. 1. Southwest Australian Margin Regional Marine 2D Seismic Survey (S310) - Areas covered by the seismic survey include the Mentelle Basin, North Perth Basin (Zeewyck and Houtman Sub-basins), Southern Carnarvon Basin and the Wallaby Plateau. Data acquired: 7300 kilometres of 2D seismic (12 second record length, 8 km solid streamer), gravity and magnetic data. In addition to the new seismic reflection data, Geoscience Australia has reprocessed selected open-file industry seismic lines in the offshore Northern Perth Basin (11,700 line km) that provides ties to most wells in the Abrolhos and Houtman sub-basins. 2. Southwest Australian Margin Marine Reconnaissance Survey - The marine reconnaissance survey investigated the geology and marine environments of the offshore North Perth and Southern Carnarvon Basins and the Wallaby Plateau. Data acquired: multibeam swath bathymetry (230,000 km2), gravity and magnetics (25,000 line km), sub-bottom profiler (25,000 line km), geological samples (190 rocks from 53 dredge sites)