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Geodetic parameters and positioning

The R / V Marcus G. Langseth is equipped with a number of positioning systems that are used for navigation functions as well as survey calculations and data processing. Knowing where the ship is and what data is being collected is extremely important for many reasons.

Reference systems for ship positioning
System equipment
Primary navigation system C-Nav dGPS
Secondary nav system Seapath dGPS
Tailbuoy navigation PosNet rGPS
Quellennavigation PosNet rGPS (1 unit per Subarray)
Acoustic DigiKurs
Navigation processing Concept print 4.3.9
Bird controller DigiKurs
Survey-Gyro (Primary) Simrad GC-80
Ship gyro (secondary) Sperry MK-27
Speed ​​log Furuno DS-50
Multibeam Kongsberg EM-122
All survey calculations will use the UTM zone (TBD at sea) projection of the World Geodetic System 1984 datum (WGS84). The Global Positioning System (GPS) works with the datum WGS84. The ship's differential GPS (dGPS) reference stations are defined in the WGS84 datum. For optimized navigation, waypoints must be given in decimal degrees (DD) to five (5) decimal places. Decimal degrees express latitude and longitude as decimal fractions and are used in many geographical information systems (GIS), web mapping applications such as Google Maps, and GPS devices. Negative numbers represent latitudes south of the equator and longitudes west of the prime meridian. Example: 38.88972, -77.00888 The geodetic and projection parameters are listed in the following tables: Geodetic parameters of the project
Geodetic parameters of the global positioning system
date World Geodetic System 1984 (WGS84)
Referenzellipsoid WGS84
Half-size axle (a) 6378137,0 m
Inverse flattening (1 / f) 298.257224
Surveying (local) geodetic parameters
date World Geodetic System 1984 (WGS84)
Referenzellipsoid WGS84
Half-size axle (a) 6378137,0 m
Inverse flattening (1 / f) 298.257224
Date transformation parameters: Global on measurement date
X shift: 0.0 m X-axis rotation: 0.0 arc seconds Scale correction: 0.0 ppm
Y shift: 0.0 m Y-axis rotation: 0.0 arc seconds
Z-shift: 0.0 m Z-axis rotation: 0.0 arc seconds
Project projection parameters - Example (varies depending on the location of the cruise)
Map projection (projection projection parameters)
Grid Universal-Want-Mercator (UTM)
Projection type Universal Transversal Mercator (UTM), Northern Hemisphere
Designated 28
Latitude at the origin 0
Longitude at origin (central meridian) -fifteen
False east 500000
Wrong nothing 0
Scaling factor at the central meridian 0.9996
Grid units Meter
Gravity binding point According to standard procedures, a gravity bond is performed before and after this cruise. Positioning of reference systems Two independent standard dGPS systems with several stations are required for the survey. Magnetic declination Magnetic declination is the angle between compass north (the direction the north end of a compass needle points) and true north (the axis around which the earth rotates). Magnetic north is determined by the earth's magnetic field and is not identical to true (or geographic) north. Depending on where you are on Earth, the angle of declination is different - in some places the geographic and magnetic poles are oriented so that the declination is minimal, but in other places the angle between the two poles is quite large. The declination is calculated using the current model of the International Geomagnetic Reference Field (IGRF). Although results are typically accurate for up to 30 minutes of arc, users should be aware of several factors that can cause interference in the magnetic field.
  • The accuracy of the model deteriorates in places near the magnetic poles.
  • With increasing time from the model era, uncertainties in estimating the secular variation lead to an ever larger difference.
  • Magnetic minerals in local geological formations cause magnetic anomalies that can sometimes be very large. These cannot be reproduced by reference field models.
  • Large magnetic storms can temporarily cause large changes in the magnetic field, especially at high latitudes.
The IGRF is a series of mathematical models of the Earth's main field and its annual rate of change (secular variation). For each cruise, the magnetic declination is calculated based on the date and location with a using Magnetfeldrechner . ‹Cruise plan to top Laboratory and science rooms›

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