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

Crowdsourced Bathymetry

From Concept to Practice
There is definite appeal to the concept of crowdsourced bathymetric data. But from where I sit as a National Hydrographer and nautical chart producer, the issues around using crowdsourced data are complex. Data quality, data processing and liability are at the top of this list. Looking into the future, we need to take a measured approach to accepting third party data for use in nautical charting to help fill in the blanks. Crowdsourcing seems to be a great solution to the problem of nearly every national hydrographic office: too much water and not enough mapping resources to survey comprehensively. Maxim... (read more)
2013-12-03 04:43:48

Satellite Derived Bathymetry Migration

From Laboratories to Chart Production Routine
Much has been said about Satellite Derived Bathymetry (SDB), but with the exception of SHOM, which led to the introduction of a number of SDB charts into the French chart series, next to nothing has been implemented within the international hydrographic community. This article aims to update readers as SDB, thanks to new generation satellites and modelling, seeing the light after going through a thirty years’ tunnel. In 2014, detailed tests and analysis conducted by government hydrographers, cartographers and recognised satellite scientists operating for a number of projects initiated by the European Space Agency, the WWF and other stakeholders, were completed,... (read more)
2015-10-12 04:09:41

EMODnet Bathymetry New Release

A new version of the EMODnet Digital Bathymetry (DTM) has recently been published which now covers all of Europe's seas. The resolution of the EMODnet DTM has been increased from 1/4 x 1/4 arc minutes to a grid with 1/8 x 1/8 arc minutes (circa 230 metres). The new DTM is based upon approx. 6,000 gathered survey datasets and composite DTMs as provided by 29 data providers from 16 countries. The new release contains data points (28.799 rows x 37.922 columns) which are divided over 16 tiles which can be downloaded freely in various formats. In addition, several upgrades... (read more)
2015-02-10 08:45:00

Google Bathymetry Improved

Google Earth now has a better zest of bathymetry. Some people comment that however (importantly) improved, the new ocean floor is not yet true 3D.   The ocean floor is colored to reflect the terrain features of the sub-sea surface. The new rendering is a bit higher resolution (much higher in places) and is more accurate than the previous version. According to the copyright messages the new ocean floor is coming from "SIO, NOAA, US Navy, NGA, GEBCO", known as good sources for bathymetry. You can see the new ocean floor by opening up Google Earth.   (read more)
2009-01-22 11:25:26

Worldwide High-resolution Bathymetry

GOMaP, the Global Ocean Mapping Project, was a plan to methodically map all the world's oceans by multi-beam sonar. It may be stalled, but swath mapping of the oceans is certainly proceeding at a brisk pace, together with efforts to fill in unmapped and poorly mapped areas. I have chosen this 'bully pulpit' to promote the goals of GOMaP. In 1999 US Navy civilian scientists calculated that an US$8-16 billion programme lasting twenty to thirty years could methodically map all the oceans deeper than 500m using multi-beam. This deep GOMaP would require 225 years of ship-time and another 600 ship/launch-years... (read more)
2008-01-01 01:00:00

Very Shallow-water Bathymetry

The River Murray Operations Unit (RMOU) of the South Australian Water Corporation surveys very shallow waters, a type of surveying that has its own specific problems overcome by non-conventional solutions. This article was submitted by a surveyor from the above survey unit. I attended the Shallow Water Survey conference in Sydney in 2003 because that is what I was doing: shallow-water bathymetry - in fact, I was even doing it out of the water. To my surprise, shallow water seemed to be considered as something at about the 10 metre mark or a bit less; 10 metres, to me, was... (read more)
2008-01-01 01:00:00

Bathymetry From Space

Global grids of synthetic bathymetry make it a simple matter to portray generalised ocean depths in all parts of the world, except the central Arctic Ocean. Derived from measurements of satellite height above the sea surface, synthetic bathymetry lacks the resolution and accuracy of acoustic soundings, plus it contains flaws that arise from measurement and computational processes. Users must therefore exercise care in the analysis and presentation of such information. In Part II of his satirical account Gulliver’s Travels into Several Remote Nations of the World, Jonathan Swift described his protagonist’s thoughts after a close-up observation of the flawed complexions... (read more)
2008-01-19 12:00:00

Southern Ocean Bathymetry

The Scientific Committee on Antarctic Research (SCAR) expert group for the compilation of the new International Bathymetric Chart of the Southern Ocean (IBCSO) proposes to build a consistent bathymetric database for digital ocean mapping of the Southern Ocean together with additional data that covers the ice shields of Antarctica, for example, radar satellite imagery, digital elevation models and free-air gravity from satellite altimetry. Acquisition, storage, compilation, and modelling of the heterogeneous data sets will be realised in a high-end GIS environment with server-GIS capabilities. Digital data processing throughout the work will facilitate the production of traditional printed maps and digital... (read more)
2007-10-27 12:00:00

Imagery-derived Bathymetry Validated

Imagery-derived Bathymetry Validated Dear Sir, I was startled by an article in the January/February 2013 issue entitled ‘Imagery-derived Bathymetry and Seabed ­Classification Validated’, which took me back to 25 years ago when I was busy validating our first official satellite chart following the launch of SPOT 1. Our ground survey had been preceded even earlier by a push-broom scanner simulation performed with a Navy P2 aircraft. What disturbs me in this remarkable display of hydrographic excellence is that the authors are attempting to cajole readers into thinking that Satellite Derived Bathymetry (SDB) is a revolution, whilst it has been in... (read more)
2013-04-02 03:09:03
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