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The International Marine Contractors Association’s (IMCA) newly published ‘Guidelines on the use of GNSS for tide calculations’ (IMCA S 027) provides an overview of how Global Navigation Satellite Systems (GNSS) can assist in more accurate real-time direct measurement of tidal changes.
As Nick Hough, IMCA’s Technical Adviser – Offshore Survey explained:
“As with horizontal positioning, vertical positioning is referenced to specified datums. Unlike land surveying, where vertical measurements (elevations) are made to and from a known, fixed position, vertical measurements offshore (depths) are taken against a moving dynamic surface.
“All absolute depths recorded from survey activities need to be adjusted for tide and reduced to a known constant vertical datum such as Mean Sea Level (MSL) or Lowest Astronomical Tide (LAT). The effect of tides will result in depth differences at different times of the day, and at the same times on different days.
“Advances in GNSS technology enable accurate and consistent calculation of height above a known datum, which means reliance on tide gauges or tide prediction tables is no longer necessary.”
IMCA S 027 includes sections on tide theory; geodetic reference systems and tidal datums; tides from GNSS; quality assurance and quality control; as well as a useful glossary, plus references and a list of further reading which includes the recently revised IMCA S 015 – ‘Guidelines for GNSS positioning in the Oil and Gas industry’ produced with IOGP. IMCA S 027 is available for members to download free of charge. www.imca-int.com
ESA has signed two contracts for an overall amount of €1.47 billion, to design and build the first batch of the second generation of Europe’s Galileo navigation satellites.
Following an intense process of open competition, these contracts have been awarded to Thales Alenia Space (Italy) and Airbus Defence & Space (Germany) to create two independent families of satellites amounting to 12 Galileo Second Generation satellites in total.
These Galileo Second Generation (G2) satellites will revolutionise the Galileo fleet, joining the 26 first generation Galileo satellites in orbit today plus the 12 ‘Batch 3’ satellites currently in production and testing. The first launch of these Batch 3 satellites will take place later this year.
The new G2 satellites will be constructed in a short time scale with their first launch expected in less than four years, allowing them to commence operations in space as soon as possible. It will gradually join the existing constellation, but will be much larger than existing satellites. Using electric propulsion for the first time, and hosting an enhanced navigation antenna, their fully digital payloads are being designed to be easily reconfigured in orbit, enabling them to actively respond to the evolving needs of users with novel signals and services.
New on-board technologies include electric propulsion to propel the satellites from the orbit in which they will be launched to the final operational orbits, allowing two satellites to be launched at once despite their increased mass. Inter-satellite links between the satellites will let them routinely cross-check their performance and reduce their dependency on the availability of ground installations. www.esa.int