If you’re looking for a marine Global Navigation Satellite System (GNSS), it can be difficult to determine the right solution for you. The purpose of this article is to make choosing the right L-Band correction service for your marine operation as easy as possible.
There are three primary choices you choose from; Real Time Kinematic (RTK), Differential GNSS (DGNSS) and Precise Point Positioning (PPP).
- Generally speaking, RTK is the fastest (no convergence time) and most accurate but requires you to set up your own base station. RTK is extremely limited in range (usually <40km of range from your station).
- Most DGNSS uses the worldwide stations of your provider. In some cases, this may restrict you to 10s of kilometers within the coast but is available without restrictions through Fugro. DGNSS is generally faster than PPP and ranges in accuracy depending on your package. DGNSS is often more expensive because the service provider has to maintain a large number of stations.
- PPP is often the cheapest solution and available globally. Prices increase significantly with higher accuracies and it’s the slowest system with the convergence speed depending in part on the accuracy required.
Offshore vs. Near-Shore
If your project operates within a small range and near the coast, such as inshore surveys, inshore hydrography, dredging, environmental surveys, mapping or construction including placement of materials, breakwaters and pylons, a near-shore DGNSS or RTK solution is likely your preferred choice.
If your situation doesn’t permit or prefer the use of a GNSS base or communication link to the base station, you’ll likely want a PPP correction service.
The accuracy and convergence time you need will depend on a large number of factors, such as whether you need precision navigation through congested marine traffic, are travelling narrow passageways or the precision required for your marine construction or drilling project. PPP is ideal for hydrographical surveying vessels, fishing vessels, seismic exploration, dynamic positioning for vessels from DP 1 to DP3, dynamic positioning for drilling and construction, including rig installations and moves, route surveys and repair of subsea structures.
Depending on the service provider, DGNSS and PPP may be offered as near-shore and offshore options. Near-shore is substantially more affordable but is limited to 10-20 km of the coast depending on the provider. If you’re looking for L-Band corrective services, you have three primary choices: Atlas, NovAtel and Fugro.
Fugro is specialized in all three and divides their services into three categories:
- Starfix is (primarily) a PPP based system aimed at offshore construction vessels, pipe and cable laying, dive support and more. Starfix has a variety of different service levels, with up to 3 cm accuracy (using a combination of PPP and other systems), with some geographical restrictions at the highest accuracies.
- Seastar is a dynamic positioning DGNSS service aimed at platform supply vessels, diving support vessels drilling rigs and more. Seastar services are available by accuracy (ranging from sub-meter to 10 cm) and satellite system.
- Marinestar® offers phase, DGPS and DGLONASS services designed for vessels travelling busy waterways, such as hydrographic vessels and dredging vessels as well as MMS operated vessels to save fuel and improve efficiency. Marinestar® is accurate to 10 cm horizontal (95%) and 15 cm vertical (95%).
- OceanstarTM is an onboard decision support system for large vessels (e.g. cruise ships, ferries, bulk carriers etc.) that enhances berthing operation and navigation in confined waters. It will allow you to achieve an accuracy of 5-10 cm.
NovAtel has also specialized in all three services, but their DGNSS service is limited to coastal areas.
- NovAtel’s RTK solution provides accuracy of 1 cm + 1 ppm horizontal and 1 cm vertical (up to 40 km baseline range).
- Novatel’s DGNSS service provides 40 cm accuracy up to 100 km of range.
- Two Novatel PPP solutions:
- NovAtel TerraStar-C is accurate to 5 cm RMS horizontal and 6.5 cm RMS vertical with 20-40 minutes convergence time
- NovAtel TerraStar-L is accurate to 40 cm RMS horizontal and 50 cm RMS vertical with less than 5 minutes convergence time
Atlas has specialized in PPP with three solutions:
- H10: with 4 cm RMS horizontal accuracy and 12-20 minute convergence times
- H30: with 15 cm RMS horizontal accuracy and 4-5 minute convergence times
- H100: with 50 cm RMS horizontal accuracy and near instant convergence times
In conclusion, if the product you’re working on is restricted to a short geographical range near the coast, where you are able set up an RTK station or use GNSS base stations, RTK or DGNSS is likely the best solution. It will provide you instantaneous convergence times and the highest accuracy (RTK). If you’re operating near-shore, but aren’t able to or prefer not to use a GNSS base station, a near-shore PPP L-Band corrective service is likely the best solution. Your specific PPP corrective service will depend on the convergence time and accuracy you require. If you’re not near-shore, offshore PPP or DGNSS corrective services are often the best choice, with the specific package depending on the convergence time and accuracy you require.
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