AEM Bathymetry

Using geophysical exploration techniques to map shallow seawater depths
Airborne Electro Magnetic Bathymetric (AEMB) mapping is useful in turbid and surf-zone waters where lidar systems are not fully effective. Coastal areas of hydrographic importance containing turbidity, shoals and channels have been surveyed. This article describes AEM systems, gives highlights from surveys in Sydney Harbour and mentions refinements that would improve bathymetric accuracy. For several decades geophysicists have been using a transmitter loop fixed to an aircraft or towed by a helicopter to emit a magnetic field into the ground to search for mineral deposits. Currents thus induced in the ground generate a return magnetic field that can be detected... (read more)
2008-01-01 01:00:00

The Science Ice Exercise Program

History, achievements and the future of SCICEX
With the end of the Cold War in 1989, the military significance of the Arctic Ocean, where submarines of the superpowers had played ‘cat and mouse’ for decades, dramatically decreased. The lessening of the classified naval operations in the Arctic prompted a small group of Arctic Ocean researchers to approach the US Navy’s submarine force and ultimately convince the service that it should (and could) provide to the civilian science community the services of a dedicated nuclear submarine for a series of research cruises to the Arctic Ocean with scientists onboard. What resulted was a unique and successful co-operative programme... (read more)
2008-01-01 01:00:00

HSA Systems

Building on hydrographic data
HSA Systems Pty Ltd was founded in Sydney Australia in 1991 as Hydrographic Sciences Australia, the founding shareholders being Brian O’Neil and Jon Dean and initial business the provision of hydrographic software and data services to the Royal Australian Navy Hydrographic Office (AHO). Paper charts in Australia in the early 1990s were largely produced using a system known as AutoChart that had its origins in the Australian Army map-making system, AutoMap. HSA provided technical and user support for this system on site at the AHO offices in North Sydney until eventually developing and implementing replacement technologies in co-operation with the... (read more)
2008-01-01 01:00:00

AUV-based 3D Chirp Sub-bottom Profiling

Offshore Diamond Mining Applications
During the 1990s De Beers Marine identified a major business opportunity in radically improving its geological modelling capability. It set up a project to deliver the necessary geophysical systems and the team soon saw potential in integrating the company’s future development ideas for Chirp sub-bottom profiling sonar and sediment characterisation with the stability and accuracy of AUVs. The result was an ultra-high-resolution, 3D-volume imaging sub-bottom profiling system capable of low-cost, large-scale, deep-water (600m) mapping from a low-specification survey support vessel. Since 2001 De Beers Marine (DBM) has been routinely operating an Autonomous Underwater Vehicle (AUV) as its principle, ultra-high-resolution geosurvey... (read more)
2008-01-01 01:00:00

Gathering Data Once, for Multiple Purposes

A Layered Approach
‘Gather once, use many times’ has applied to bathymetric data gathering for many years, particularly in public bodies and organisations. Whilst understandable and desirable to have one infinitely adaptable dataset appealing to all users, it is mainly driven by the desire to achieve cost savings. There is nothing wrong with that, it just has not made it beyond being a tag line. The reasons for this are not clear but maybe aspiration does not match reality in the bathymetric market, environment, industry or clients. Why has ‘gather once’ not been widely implemented? What concept could replace it and actually progress... (read more)
2013-12-04 11:30:00

Marine 3D Full Tensor Gravity Gradiometry

The first five years
3D Full Tensor Gradiometry (FTG) or high-precision moving platform gravity gradiometry measures the full gravity field in all directions. The technology was initially commercialised for the petroleum exploration industry to assist with defining complex salt structure/geometry, sub-salt play definition and the re-imaging of seismic data using techniques such as Pre and Post-Stack Depth Migration (PSDM). The scope of gradient data utility further ranges from prospect level to regional reconnaissance project evaluation. Integration with other geophysical datasets produces added value in the form of improved interpretation accuracy and risk reduction. FTG data contains critical directional information and greater resolution than does... (read more)
2008-01-01 01:00:00

3D Web-mapping

Integrating Marine Data into Google Earth
Google Earth has become a popular 3D web-mapping viewer, mainly due to the richness of satellite imagery in its primary database. However, the database contains very limited marine data. While the addition of marine data would be welcome, this article explores the use of Web Map Service (WMS) and Keyhole Markup Language (KML) to overlay large-scale multi-beam imagery datasets from the Irish National Seabed Survey into the Google Earth viewer. Over the last seven years the Irish National Seabed Survey (INSS) has returned many terabytes of multi-beam sonar and ancillary data, providing detailed bathymetry data and knowledge of seabed characteristics.... (read more)
2008-01-01 01:00:00

Benthic Habitat Mapping

Utilisation of Multi-beam Backscatter for Ecological Study of the Seafloor
The establishment of multi-beam echo sounders (MBES) as a mainstream tool in ocean mapping has revolutionised approaches towards nautical charting, seafloor geotechnical/geological surveys and benthic habitat mapping. The resolution of bathymetric and backscatter data collected by MBES has improved significantly in recent years through technological improvements of these acoustic systems. Furthermore, developments in data collection and processing of MBES backscatter have resulted in the increasing preferential use of multi-beam technology over conventional side-scan sonar or single beam sonar for these applications. This article explores some recent developments in the methods used to generate benthic habitat maps using multi-beam sonar systems.... (read more)
2012-07-26 02:55:45

GIS Analysis Tools in Submarine Cable Planning

While the advantages of Geographic Information Systems (GIS) for storing and displaying spatial data are widely recognised, the analytic capabilities are less well known outside the GIS community. Extensions to core GIS software make possible new information, insights and better understanding of spatial relationships. GIS analysis functions can identify locations that meet a set of criteria, reclassify data to a common class-scale, weight datasets and combine these to analyse suitability or adherence to a given set of rules. GIS provides the framework for solving complicated problems. The output can be displayed on a map, where relationships are apparent and solutions... (read more)
2008-01-01 01:00:00

GPS for Global Tidal Measurements

Recent data analysis heralds applications for hydrography
Hydrographers require accurate three-dimensional positions of the survey vessel and typically use differing methods for resolving the horizontal and vertical components. GNSS, such as the Navstar Global Positioning System (GPS), have become the dominant horizontal positioning system for hydrographic operations, whereas tidal estimation is the foremost method used in determining vertical positioning. The tidal estimation method integrates a water level measurement at a remote location with a predicted propagation of the tidal wave, to establish a sea surface level at the desired location. This paper investigates a new method using GNSS as an aid in improving these water level estimates... (read more)
2008-01-01 01:00:00
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