|To ensure the early interoperability of Europe’s satellite navigation with GPS, the four Galileo satellites have begun broadcasting the ‘offset’ between the parallel navigation systems’ timings, accurate to a few billionths of a second. With satellite navigation based around the highly accurate measurement of signal times, both Galileo and GPS have their own internal reference time systems used to synchronise all system clocks and signals.|
The problem is that these time systems are not quite identical, with Galileo System Time being around 50 nanoseconds or less apart from GPS time.
A nanosecond is only a billionth of a second, corresponding to the time light takes to travel 30cm, explained Jörg Hahn, Galileo System Engineering Manager. But this soon adds up, and anyone attempting to use the two systems together might find this ‘offset’ accounting for up to 15m of error, causing an unacceptable contribution to user performance.
Instead, this time offset needs to be known or estimated by the receiver itself. The dissemination of the GPS to Galileo offset can help in constrained environments such as city centres, where only a few satellites are visible in the sky, added Hahn.
The receiver can then take this offset and align all the observations to a single time scale, reducing the computational burden on the receiver since the amount of unknowns are decreased. Accordingly, disseminating the offset will help enable the user receiver market to start making use of Galileo at this early stage, with only four satellites currently in orbit.
Formally known as the GPS to Galileo time offset, GGTO, the accuracy of the offset is being benchmarked at five nanoseconds or less.
A tale of two times
Galileo runs on Galileo System Time, GST, which is generated on the ground at the Galileo Control Centre in Fucino, Italy, by the Precise Timing Facility, based on averages of different atomic clocks. GPS time is computed by the GPS control segment.
These two internal times are derived independently on one another but are kept close to the world’s reference time, UTC, with the offset between the two being precisely calculated on a continuous basis by the PTF and the resulting GGTO distributed through Galileo’s navigation message.
GPS and Galileo share some frequencies (L1/E1 at 1575.420 MHz and L5/E5a at 1176.450 MHz) with a view to interoperability, and disseminating the GGTO makes using the two systems together more straightforward still.
GGTO determination methods and interface design were agreed on a preliminary basis between the Galileo Project and the US Naval Observatory back in 2003, through a GGTO subgroup of the US and EU Working Group A on Compatibility and Interoperability, Jörg Hahn explained. They have been working together closely since then to make the GGTO a reality.
Friday, May 10, 2013
Wednesday, May 8, 2013
|MMT Group (Sweden) and Reach Subsea AS (Norway) have signed a Letter of Intent for the purpose of establishing a new joint venture within offshore survey operations. The companies have, together with the engineering company Kystdesign, developed a new generation of high-speed survey ROVs called 'Surveyor', with the intention to build the first unit in 2013 and be ready for offshore operations in 2014.|
The new entity will deliver subsea services such as general offshore survey, lay support, seabed mapping and pipeline/structure inspections from a dedicated DP2 vessel to be chartered in by the joint venture.
Together, the two companies employ a total of 300 people who are involved in offshore work and the subsea energy market. The offices are presently in Haugesund (Norway), Gothenburg (Sweden) and Banbury (United Kingdom). The joint fleet consists of 7 vessels, 7 ROVs and 2 ROTVs with further units to be delivered next year.
Friday, May 3, 2013
|Located in Linköping, Sweden, a test tank of 6m deep and 10m in diameter, containing 470 cubic metres of water, will allow new underwater systems technology to be trialled and tested in a controlled environment rather than in a lake or at sea. Saab sees the facility bringing significant savings in time and costs, whilst offering a unique opportunty to develop and trial underwater systems that will future strenghen its product portfolio.|
Saab has a world leading position in the field of unmanned underwater vehicles and is the world's largest manufacturer of electric remotely operated underwater vehicles (ROVs). Typical applications are offshore energy, mine reconnaissance and location of accident victims. With Saab's underwater technologies, these jobs can be performed reliably and cost-effectively.
Friday, April 5, 2013
High resolution, cost effective shallow-water surveys now possible on small boats
Kongsberg Maritime will introduce the new EM 2040 Compact, a sophisticated multibeam echo sounder for high resolution mapping and inspection applications, during Ocean Business 2013. Based on the state-of-the-art EM 2040 multibeam, the EM 2040C is a significant development in acoustic technology that makes highly detailed surveys of shallow water possible using small boats and launches. Kongsberg Maritime will also offer another variant, the EM2040CX for use on AUVs, ROVs and other vessels of opportunity.
Available in single or dual head configurations, the EM 2040C is the natural successor to Kongsberg Maritime's established compact multibeam, the EM 3002. Because the EM 2040C is based on the most sophisticated shallow water multibeam technology platform available today, it offers significantly improved performance over the EM 3002, whilst still being suitable for use aboard small vessels.
The EM 2040C ensures that highly accurate data is available in real-time. This makes it possible to conduct very cost-effective surveys with lower requirements for post-processing, due to the high quality of data available. Application possibilities include port and harbour surveys, post-dredging surveys, shipwreck exploration, habitat mapping, pipeline inspection and hydrographic surveys to a standard that exceeds IHO S44 and LINZ performance requirements.
The EM 2040C features high resolution and a wide frequency range from 200 to 400 kHz, with frequency selection in steps of 10 kHz. It uses Frequency Modulated (FM) chirp to extend range and offers a maximum depth of 490m with a beam width of 1° x 1° at 400 kHz. In dual configuration, with two Sonar Heads tilted to each side, 200º total coverage can be achieved, which enables surveying to the water surface or up to 10 times water depth on flat bottoms.
"The EM 2040 Compact introduces a wealth of new possibilities by providing the same levels of clean & accurate data as the highly acclaimed EM 2040 multibeam whilst being similar in size to our existing compact multibeam, the EM 3002," comments Helge Uhlen, Product Sales Manager, Kongsberg Maritime. "This means that highly detailed data, which requires no, or very little post processing, can be available for a much wider range of survey applications."
KONGSBERG multibeam systems are recognised for high sounding accuracy, dense pattern of soundings to cover the seafloor, excellent build quality and robustness. In addition to the soundings, all KONGSBERG multibeam echo sounders produce water column data and seabed image data similar to a side scan sonar image. The water column data is useful to detect the shallowest depth or for displaying objects and features in the water column such as seeps and tops of masts, etc. The seabed image is useful for characterising the seabed and can detect features not visible in the sounding data.
Kongsberg Maritime has created a straightforward upgrade path from the EM 3002 compact multibeam to the new EM 2040C. For a limited time, EM 3002 owners will also be offered a discount on exchange of EM 3002 components when upgrading to EM 2040C.
Tuesday, March 12, 2013
Europe’s new age of satellite navigation has passed a historic milestone – the very first determination of a ground location using the four Galileo satellites currently in orbit together with their ground facilities.
This fundamental step confirms the Galileo system works as planned.
A minimum of four satellites is required to make a position fix in three dimensions. The first two were launched in October 2011, with two more following a year on.
“Once testing of the latest two satellites was complete, in recent weeks our effort focused on the generation of navigation messages and their dissemination to receivers on the ground,” explained Marco Falcone, ESA’s Galileo System Manager.
This first position fix of longitude, latitude and altitude took place at the Navigation Laboratory at ESA’s technical heart ESTEC, in Noordwijk, the Netherlands on the morning of 12 March, with an accuracy between 10 and 15 metres – which is expected taking into account the limited infrastructure deployed so far.
This fix relies on an entirely new European infrastructure, from the satellites in space to the two control centres in Italy and Germany linked to a global network of ground stations on European territory.
“The test of today has a dual significance: historical and technical, “notes Javier Benedicto, ESA’s Galileo Project Manager.
“The test of today has a dual significance: historical and technical," notes Javier Benedicto, ESA’s Galileo Project Manager.
“From the historical perspective, this is the first time ever that Europe has been able to determine a position on the ground using only its own independent navigation system, Galileo.
“From the technical perspective, generation of the Galileo navigation messages is an essential step for beginning the full validation activities, before starting the full deployment of the system by the end of this year.”
With only four satellites for the time being, the present Galileo constellation is visible at the same time for a maximum two to three hours daily. This frequency will increase as more satellites join them, along with extra ground stations coming online, for Galileo’s early services to start at the end of 2014.
With the validation testing activities under way, users might experience breaks in the content of the navigation messages being broadcast. In the coming months the messages will be further elaborated to define the ‘offset’ between Galileo System Time and Coordinated Universal Time (UTC), enabling Galileo to be relied on for precision timing applications, as well as the Galileo to GPS Time Offset, ensuring interoperability with GPS. In addition, the ionospheric parameters for single frequency users will be broadcast at a later stage.
A European partnership
The definition phase and the development and in-orbit validation phase of the Galileo programme were carried out by ESA and co-funded by ESA and the European Community.
The Full Operational Capability phase is managed and fully funded by the European Commission. The Commission and ESA have signed a delegation agreement by which ESA acts as design and procurement agent on behalf of the Commission.
Thursday, February 28, 2013
UK-based companies NCS Survey and InterMoor have awarded Veripos a new three-year contract for provision of GNSS positioning services. The contract will be in support of their respective activities, particularly in and around the North Sea and Brazilian offshore sectors.
Facilities to be supplied include a full range of proprietary satellite positioning capabilities, including the company’s latest Apex2 service utilising Precise Point Positioning (PPP) methods in conjunction with both GPS and Glonass constellations. A range of modular hardware comprising versatile integrated mobile units which can be configured to accommodate a wide range of positioning solutions will also be provided, together with suites of processing software for determining and validating quality control data.
Wednesday, February 6, 2013
|Unique System FZE, a Unique Maritime Group Company, UAE, along with The Geodesy and Hydrographic Survey Section of Dubai Municipality have established a permanent tidal station at Al Mamzaar. The purpose of the project is to collect precise Tide Data continuously for a period of 19 years for mean sea level calculation, annual sea level rise and to provide precise tide and its related meteorological data to various users and to define and update a precise vertical datum for Dubai Emirate.|
Dubai Municipality’s Geodesy and Hydrographic Survey Section of Dubai Municipality has several components comprising of various sub-systems that provide real time monitoring, alerts, warnings and timely dissemination of information to concerned departments.
There is no such permanent tidal station elsewhere in the Gulf region and this is first time in the history of Middle East, such a scientific project is being executed. As a result of significant dredging and construction in the near shore / offshore area of Dubai Emirate the sea level has risen and also due to global warming the Geodesy and Hydrographic Survey Section of the Survey Department, Dubai Municipality, felt the need of a Permanent Tide Gauge Station in the Gulf sea.
The Survey Department of Dubai Municipality already had a network of five coastal and offshore tide/meteorological stations which are monitoring and recording tide/met data from 2004 onwards. The surveyors, mariners, fishingcommunity, marine /offshore / near shore construction engineers, hydrographers, Coastal Management Group and the navigators are most benefitted by the tidal information.
Following is the output from the network of tidal stations:
1. Very precise daily tidal variation, annual mean sea level variations, sea level rise due to tsunami /earthquakes/low pressure etc…
2. Atmospheric pressure, atmospheric temperature and sea water temperature, which are the basic reasons for sudden variations in sea levels.