GPS and Acoustic USBL Positioning

Brief Description of GPS and Australian Datums

Because of its reliability, accuracy, and ease of use, the Global Positioning System (GPS) has become the overwhelming choice for providing accurate position control during most field survey operations. The CRC is using the Fugro differential beacon network which provides extensive world wide coverage.

Australian Survey Datums.

The CRC used the Fugro Starfix DGPS systems.

 

Back to top of page


Geocentric Datum Australia - GDA94

Positioning coordinate data is referenced and presented in Geocentric Datum of Australia 1994 (GDA94). The Global Positioning System ( GPS ) operates on the World Geodetic System 1984 (WGS84) datum. The Fugro Starfix Differential GPS Reference Stations are currently defined in the International Terrestrial Reference Frame 2000 (ITRF2000 Epoch 2006.25. Due to the continual refinement of the WGS84 Reference Frame, the WGS84 and ITRF2000 Reference Frames are essentially identical. Grid coordinates are referenced in meters to the Map Grid of Australia ( MGA), which is a Transverse Mercator (TM) with a Latitude of Origin being 0 degrees North, a Central Scale Factor of 0.9996, False Easting of 500 000.000m, False Northing of 10 000 000.000m and a Central Meridian dependant on locality.

Bathymetry is reduced to Mean Sea Level (MSL) using tidal observations taken from established tide gauges operated by the National Tidal Facility in Adelaide.

Ellipsoid Parameters Ellipsoid Name GRS80 (MGA94) (GDA) WGS84
Major Semi Axis a 6378137 6378137
Inverse Flattening 1/f 298.2572221 298.2572236
Flattening f = 1 / f 0.003352811 0.003352811
Minor Semi Axis b = a * ( 1 - f ) 6356752.314 6356752.314
Eccentricity e 0.081819191 0.081819191
Eccentricity squared e **2 = 2f - f**2 = ( a **2 - b **2 ) / a **2 0.00669438 0.00669438
Second Eccentricity e' 0.082094438 0.082094438
Second Eccentricity squared e' **2 = e **2 / ( 1 - e **2 ) = ( a **2 - b **2 ) / b **2 0.006739497 0.006739497

Back to top of page


Surface Positioning

The Global Positioning System (GPS) has led to rapid advances in positioning accuracy and survey efficiency. Fugro is a stakeholder in the Coastal CRC through it contribution to the Coastal CRC of the use the use of the Fugro Starfix GPS Positioning. Fugro is at the forefront of the latest developments in positioning, with products and services that continue to set new standards. In benthic habitat mapping, as in most dynamic surveys, accurate and precise positioning is a primary requirement. Fugro's state of the art STARFIX© Differential GPS (DGPS) service has been developed specifically to meet the offshore community's demand for highly accurate positioning world-wide.

The following systems are used in the habitat mapping case studies and were made available by Fugro:

Starfix XP SDGPS (+/- 10 cm in x-y, +/- 15 cm in z).

Starfix HP DGPS (+/- 20 cm in x-y, +/- 30 cm in z).

Starfix L1 DGPS (+/- 3 m in x-y only).

HF DGPS (Deltafix) (+/- 3m in x-y only).

Back to top of page


Starfix DGPS Services

Differential GPS algorithms, developed by Fugro, remove natural and man-made errors from the US Department of Defense's orbiting satellite Global Positioning System. Fugro's STARFIX© DGPS service has access to more than 130 land based reference stations, with permanently manned control centres in Houston, Aberdeen and Perth. Real-time data is delivered world-wide over a network of high and low power satellite links.

Back to top of page


Sub-Sea Tracking:- Acoustic Positioning

The tracking of towed sensors such as side scan, shallow seismic systems and video camera sleds was carried out using Geoscience Australia's USBL acoustic underwater positioning systems. Using Ultra Short Baseline (USBL) and combined with surface GPS provides the highest levels of accuracy for sub-sea navigation and positioning.

Back to top of page