GPS/DGPS

Marine GPS and DGPS: 

 

Marine GPS (Global Positioning System) and DGPS (Differential GPS) are critical components in modern marine navigation, helping vessels determine their precise position, velocity, and time. They are widely used for safe and efficient navigation on the open sea, enabling mariners to avoid hazards, plan routes, and maintain their course.

 

1. Marine GPS (Global Positioning System)

Marine GPS systems rely on a network of satellites that transmit signals to GPS receivers. The GPS receiver calculates the time it takes for the signal to reach the receiver, allowing it to determine the exact location (latitude, longitude, and altitude) of the vessel. Marine GPS is essential for navigating in open water, especially in situations where traditional landmarks are unavailable.

 

How Marine GPS Works:

 

Satellites: GPS uses a constellation of 24 satellites that orbit the Earth. The satellites continuously broadcast signals, and GPS receivers pick up these signals.

 

Triangulation: By receiving signals from at least three satellites, the GPS receiver uses triangulation to determine the vessel’s position in terms of latitude and longitude.

 

Accuracy: Standard GPS can offer an accuracy range of approximately 5 to 15 meters, but this can vary depending on factors like satellite geometry, signal interference, and atmospheric conditions.

 

Features of Marine GPS:

 

Route Planning: Marine GPS systems allow users to plot and save routes and waypoints.

 

Real-Time Positioning: Provides continuous updates on the vessel's position, speed, and course.

 

Waypoints and Navigation Aids: GPS can store pre-programmed waypoints to guide the vessel along its planned route.

 

Integration with Other Marine Systems: Marine GPS is often integrated with other systems like radar, ECDIS (Electronic Chart Display and Information Systems), sonar, and autopilot to provide a full navigation solution.

 

2. Differential GPS (DGPS)

 

DGPS is an enhancement to the standard GPS, providing more accurate positioning information by correcting the errors from the standard GPS signal. It uses a network of land-based reference stations to transmit correction signals to GPS receivers, significantly improving the accuracy of the system.

 

How DGPS Works:

Reference Stations: DGPS stations are located at known, fixed locations on land and measure the errors in the GPS signals.

Correction Signals: The reference stations calculate the difference between the GPS signal’s position and the known position, then broadcast a correction signal.

Receiver Correction: Marine vessels equipped with DGPS receivers can receive these correction signals and adjust their position calculations, improving accuracy to within 1 to 3 meters (compared to the typical 5–15 meters of standard GPS).

 

Types of DGPS:

 

Standalone DGPS:

A standalone DGPS system relies on the DGPS signal from a single reference station, improving accuracy for local navigation.

 

Integrated DGPS:

Integrated DGPS systems combine GPS and other systems like radar, chartplotters, and AIS, offering a more comprehensive navigation solution.

 

Wide Area DGPS (WADGPS):

WADGPS provides corrections over a broader area using a network of reference stations. The U.S. Coast Guard and other organizations maintain such systems to cover large maritime areas.

 

Real-Time Kinematic (RTK) DGPS:

RTK DGPS is a more advanced system that provides centimeter-level accuracy by using real-time corrections. It is commonly used in high-precision applications like surveying, construction, and autonomous navigation.

 

Advantages of Marine GPS and DGPS:

 

Marine GPS:

Global Coverage: Provides positioning anywhere in the world.

Simple to Use: The GPS system is easy to use and does not require land-based infrastructure.

Real-Time Navigation: Continuous updates and accurate positioning data for vessel navigation.

 

DGPS:

Higher Accuracy: DGPS improves GPS accuracy from the standard 5–15 meters to 1–3 meters.

Reduces Navigation Errors: Helps mariners avoid errors caused by ionospheric delay, signal interference, or multipath errors.

Safety: DGPS enhances safe navigation, especially in congested or hazard-prone waters.

 

Marine GPS and DGPS Systems: Types and Features

 

Handheld GPS Units:

Portability: These are portable, battery-operated GPS devices commonly used for recreational boating, fishing, or hiking. They offer basic navigation functionality, including positioning, route planning, and waypoint tracking.

Example Models: Garmin GPSMAP 66i, Lowrance Hook Reveal 5.

 

Fixed Marine GPS Units:

Installation: Fixed marine GPS units are installed on vessels and are designed for continuous, real-time navigation. They often come with larger screens and integrate with other marine systems like radar, sonar, and chartplotters.

Example Models: Garmin GPSMAP 8600 Series, Simrad GO Series, Raymarine Axiom.

 

Chartplotters with GPS Integration:

These systems combine GPS with electronic charting capabilities, allowing mariners to visualize their position, routes, and nearby hazards on detailed digital maps.

Example Models: Garmin Echomap Ultra Series, Lowrance HDS Live, Raymarine Axiom Pro.

 

DGPS Receivers:

DGPS receivers are installed aboard larger vessels or used in applications requiring enhanced positioning accuracy. These systems receive the correction signals from a DGPS network, typically from a Coast Guard or similar service.

Example Models: Furuno GP-170 (DGPS), Trimble R8 GNSS (DGPS/RTK).

 

Popular Marine GPS and DGPS Brands:

 

Garmin:

Garmin is one of the leading manufacturers of marine GPS systems, offering a wide range of models from portable GPS units to advanced chartplotters with integrated GPS and DGPS.

Popular Models: Garmin GPSMAP Series, Garmin Echomap Ultra, Garmin STRIKER Series.

 

Raymarine:

Raymarine provides integrated GPS systems that combine high-resolution displays, charts, and advanced navigation tools.

Popular Models: Raymarine Axiom Series, Raymarine Dragonfly 7, Raymarine i70/i70S.

 

Simrad:

Simrad offers both GPS receivers and full-fledged navigation systems that integrate GPS, radar, sonar, and chartplotters for seamless navigation.

Popular Models: Simrad GO Series, Simrad NSS Evo3, Simrad NSO Series.

 

Furuno:

Furuno is known for high-quality GPS and DGPS systems, commonly used on commercial vessels, and offers systems with integrated radar and sonar.

Popular Models: Furuno GP-170, Furuno GP-39 (DGPS), Furuno NAVnet TZT3.

 

Lowrance:

Lowrance offers affordable and reliable GPS systems, often used in recreational boating and fishing.

Popular Models: Lowrance HDS Live, Lowrance Elite FS, Lowrance Hook Reveal.

 

B&G:

B&G specializes in GPS and navigation systems for sailing yachts, offering integrated chartplotters, GPS, and wind instruments.

Popular Models: B&G Zeus3, B&G Vulcan 7.

 

Trimble:

Trimble offers high-precision GPS and DGPS systems, primarily used in commercial, surveying, and scientific applications.

Popular Models: Trimble R8 GNSS, Trimble GeoExplorer.

 

JRC (Japan Radio Co.):

JRC provides integrated GPS solutions, including DGPS receivers, often used on commercial ships and marine vessels.

Popular Models: JRC JMA-5200 GPS, JRC JGN-6 DGPS.

 

Conclusion:

Marine GPS and DGPS systems are indispensable tools for safe and accurate navigation at sea. While GPS offers basic positioning, DGPS enhances accuracy by using correction signals, making it essential for commercial vessels or areas with critical navigation needs. There are a variety of devices and systems available, from handheld units for recreational users to sophisticated integrated solutions for large vessels. Choosing the right system depends on the specific needs of the vessel, such as the required level of accuracy, integration with other systems, and the type of navigation being done. Top brands like Garmin, Raymarine, Simrad, and Furuno lead the market, offering reliable and advanced solutions for marine navigation.