LBL Underwater Positioning

Long baseline (LBL) positioning has many applications both commercially and in research, from surveying a ship hull to positioning offshore platforms in deeper waters. The technique consistently provides accuracies in the order of decimetres over large areas, independent of depth. Recent advances include the integration with other acoustic techniques or with inertial navigation systems for greater levels of accuracy. Since navigation by GPS isbased on electromagnetic signals that cannot penetrate water, subsea positioning requires a different approach. As sounds waves travel through the sea they alternately compress and decompress the water molecules; these compressions/decompressions are detected as changes in pressure.... (read more)

2008-01-19 12:00:00

A Note on Fifty Years of Multi-beam

The Early Years

The year 2013 marks the Fiftieth Anniversary of the first installation of a multi-beam sonar sounding system. A review of the early development of multi-beam sonar systems follows. On 1 May 1960, a United States U-2 spy plane flown by Francis Gary Powers was shot down over the USSR by a Russian Dvina surface to air missile. This event, although it would seem not to be related, led directly to the development of multi-beam sonar according to the autobiographical memoir, Lazarus: From Seven to Seventy by Eugene Weisberger, then general manager at General Instrument. The U-2 had flown spy missions over the... (read more)

2013-05-22 04:51:42

The Making of RV Kronprins Haakon

New Norwegian Ice-breaking Research Vessel

Norway is a maritime country with a very long coastline, plus it is very much a polar nation with 80% of its sea territory and 45% of its land mass north of the Arctic circle. It is the only country with territorial claims both in the Arctic and the Antarctic. In spite of this, Norway has not had a purpose-built polar research vessel since Roald Amundsen’s Maud (1917), having instead relied on converted commercial vessels for such purposes. That has all changed, however, now that Kronprins Haakon has come into service. This article provides insight into the making of this new multi-purpose research... (read more)

2018-04-17 10:51:23

What’s Down Below??

Why ROTVs are Useful Tools in Answering This Question

Early in the first quarter of 2007, Noordhoek Survey took delivery of two MacArtney Focus-2 Remotely Operated Towed Vehicles (ROTVs). The expectation was that the new ROTVs would be a valuable addition to the existing fleet of underwater vehicles. Now, half a year and hundreds of survey kilometres later, these expectations have proven to be correct.<P> Over the past 15 years, Noordhoek has gained valuable experience in ROV and towfish surveys. The new Focus-2 ROTVs fill the gap that used to exist between the specific competences of these two survey platforms. The ROTV body (1.25x1.25x1.85m) consists of four carbon-fibre hulls,... (read more)

2007-11-27 12:00:00

Multibeam Mapping of Continental Margin Morphology

Bathymetry in understanding oceanic & continental evolution

A jigsaw puzzle of lithospheric plates comprises the outer shell of the earth. Oceanic plates, formed by ascending magma at mid-ocean ridges and transported towards the continents by internal convective forces, collide with continental plates at convergent margins and are subducted beneath them. This is accompanied by violent geological processes such as earthquakes, volcanic eruptions, submarine landslides and tsunamis. The speed of drift of the plates is in the order of several centimetres per year, too slow to be observed directly. Still, these processes shape the surface of the ocean bottom and submarine morphology records these forces acting on the... (read more)

2008-01-01 01:00:00

USBL in Dam Survey by ROV

An USBL underwater positioning system is the ideal solution for dam survey by ROV, providing easy and fast set-up and accurate 3D measurement for traceability, but not all USBL systems can meet the demands of this environment. PLSM (France) has developed a light and polyvalent system for use in shallow water down to 300 metres. The author describes AQUA-METRE R300 and some typical results. In France, ten-yearly dam inspection is mandatory for medium to large dams. There are about three hundred dams between the Pyrenees and Brittany. The main goal is to survey the submerged concrete wall in order to... (read more)

2008-01-01 01:00:00

Surveying Deep-water Seeps at Convergent Continental Margins

On geological time scales, the floor of the ocean is young compared to the continents, as it is continuously recycled by internal convective forces. Oceanic lithosphere forms by ascending magma at mid-ocean ridges and is consequently transported towards the continents. At convergent margins it is subducted beneath them and ultimately transferred back into the Earth’s interior. During their lifetime the oceanic lithosphere becomes cooler and heavier, and increasingly more sediments are deposited on top of them. During subduction, the oceanic crust with its overlying sediments is brought to great depths and exposed to high pressure and temperature. As a result... (read more)

2008-01-01 01:00:00

Quality Control of Survey Data

A Continuous Process?

Quality control of survey data is an integral part of any hydrographic survey or inspection operation, but the focus is too often concentrated on the wrong sensors, the carrying out of unnecessary comparisons and ultimately burying real issues in a flood of confusing and contradictory error messages, print-outs and alarms. So what is meant by quality control of survey data, why do we need it, how should we measure it and when is the best time to carry it out? ‘Quality’ is a phrase often used and is expected to be highly visible in the literature and mission statements of... (read more)

2013-09-06 04:37:34

Hydrographic Use of Satellite Imagery in South Pacific

The French Hydrographic Office (SHOM) uses remotely sensed visible imagery for the cartography of atolls and reefs. It is considered as an efficient and relatively inexpensive method to collect information where data is sparse. Remotely sensed visible imagery is used in Pacific French Overseas territories for the cartography of atolls, reefs et cetera. All shallow-water areas may be involved, in particular when the cost of usual hydrography would be out of proportion with maritime traffic. Remotely sensed imagery is mixed with all field information available (bathymetry, buoys, seamarks) and a ‘spatiocarte’ (spatio-chart) is produced, which provides information on: Land: coastline,... (read more)

2008-01-01 01:00:00

Successful Delivery of Coastal Survey Data to the Royal Australian Navy

IHO Order 1b Bathymetric Lidar Data

Amongst the largest contracted coastal hydrographic Lidar survey projects awarded in recent years is the Australian Hydrographic Service (AHS) survey of the Torres Strait in Northern Queensland. The intent of this very large survey was to update nautical charting in the region, facilitate safer navigation and enhance the capacity of maritime enforcement vessels to protect and secure Australian waters from incursions by illegal foreign fishing vessels. As it was to be used for international chart products, the survey data had to be of an accordingly high standard. Approximately 850km north from Cairns, the Torres Strait forms the confluence between the... (read more)

2010-05-31 10:44:08