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

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

Near-shore Bathymetry

Geospatial products and ecological applications

Bathymetric data has traditionally been important for producing nautical charts in support of safe navigation. Hazardous environmental conditions and technological restraints have, however, limited the ability to acquire near-shore data. The National Oceanic and Atmospheric Administration (NOAA) has made great strides in bringing together hydrography, geodesy, tides and remote-sensing data to provide essential information for the coastal manager. New technology such as Light Detection and Ranging (Lidar), VDatum (a vertical datum transformation tool) and GPS has given us the capacity to acquire and integrate near-shore bathymetric, shoreline and topographic data. This has in turn allowed us to increase our knowledge... (read more)

2008-01-01 01:00:00

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 1.092.115.678 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

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

UK Seas Bathymetry

SeaZone has announced the availability of detailed water depth data for seas around the UK. It has taken the company 2 years capturing and processing hydrographic survey data to create a database of the underwater terrain. Uses include the creation of surface models, volumetric or rate of change calculations, and as input into hydrodynamic or environmental models often used for site selection, route definition and seabed mobility studies. SeaZone's Digital Survey Bathymetry extends across the majority of the UK continental shelf and represents the most detailed information of water depth available. It is much more accurate and detailed than... (read more)

2009-04-14 03:31:27

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

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

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