Difference Between GNSS and GPS Explained
July 06, 2026Most mariners use the word "GPS" for any satellite position fix on the bridge. In practice, a modern receiver is often pulling signals from satellites operated by four or five different countries at once. That system is GNSS, and the distinction between GNSS and GPS matters more than the shared vocabulary suggests. Here is what separates the two, why the difference is relevant aboard commercial vessels, and how the technology connects to the equipment and charts a vessel already carries.
What Is GNSS?
GNSS stands for Global Navigation Satellite System. The term refers to any satellite constellation that provides positioning, navigation, and timing data with global coverage. GNSS is an umbrella term, not a single system. Under that umbrella sit all the national and regional satellite networks a receiver can use.
The four fully operational global constellations are:
- GPS (United States), with approximately 31 operational satellites.
- GLONASS (Russia), with 24 operational satellites.
- Galileo (European Union), with 30 operational satellites.
- BeiDou (China), with 35 operational satellites.
Regional systems such as QZSS (Japan) and NavIC (India) supplement these with coverage over specific areas. A GNSS receiver can combine signals from some or all of these constellations, accessing well over 100 satellites worldwide.
What Is GPS?
GPS stands for Global Positioning System. GPS is the satellite navigation constellation operated by the United States Department of Defense, designated NAVSTAR GPS. Operational since 1978 and available globally for civilian use since 1994, GPS was the first satellite navigation system to achieve worldwide coverage and remains the most widely recognized.
A GPS-only receiver can access signals from the approximately 31 satellites in the U.S. constellation. When buildings, terrain, or atmospheric conditions block enough of those signals, the receiver loses its position fix until signals become available again. A GNSS receiver avoids this limitation by switching to satellites from other constellations when GPS signals are obstructed.
GNSS vs GPS: The Key Differences
The simplest way to understand the distinction: GPS is one satellite constellation. GNSS is the full set of constellations. Every GPS receiver uses a GNSS system, but not every GNSS receiver is limited to GPS.
| Feature | GPS | GNSS |
|---|---|---|
| What it is | A single U.S. satellite constellation | The umbrella term for all satellite navigation systems |
| Satellites available | Approximately 31 (U.S. only) | 100+ across GPS, GLONASS, Galileo, BeiDou, and regional systems |
| Operated by | United States Department of Defense | Multiple nations and agencies |
| Coverage | Global, but limited to one constellation | Global, with redundancy across multiple constellations |
| If signals are blocked | Position fix may be lost until GPS signals return | Receiver switches to other constellations |
For a mariner, the practical difference comes down to reliability. A multi-constellation GNSS receiver maintains a position fix in conditions where a GPS-only receiver might struggle, such as near tall port infrastructure, in high-latitude waters, or during atmospheric interference.
Why GNSS Matters for Maritime Navigation
SOLAS Chapter V requires all vessels to carry a global navigation satellite system or terrestrial radionavigation receiver to establish and update the vessel's position at all times throughout the voyage. IMO currently recognizes GPS, GLONASS, BeiDou, Galileo, and NavIC as components of the World-Wide Radionavigation System.
Most modern bridge equipment, including ECDIS and AIS transponders, feeds position data from the vessel's satellite receiver. That position is what places the vessel on an electronic navigational chart and drives the automatic position reports AIS broadcasts to surrounding traffic. A loss of satellite fix affects the accuracy of every system downstream.
A multi-constellation GNSS receiver reduces the risk of losing that fix. More available satellites mean better geometry for calculating position, which typically improves both accuracy and availability. For vessels transiting congested ports, high-latitude routes, or areas where one constellation has limited coverage, the redundancy GNSS provides is a meaningful operational advantage.
GPS, GNSS, and the Equipment on Your Bridge
Understanding the distinction helps when evaluating bridge navigation equipment. A receiver marketed as "GPS" may in fact be GNSS-capable, using multiple constellations without labeling them individually. Conversely, an older GPS-only receiver accesses only the U.S. constellation, which may be adequate in open water but offers less redundancy in constrained environments.
When specifying or replacing satellite receivers, the key questions are which constellations the receiver supports, whether it meets the applicable IMO performance standards, and whether it integrates with the vessel's ECDIS and AIS. Officers responsible for passage planning should also confirm that the receiver's position output matches the datum used by the vessel's charts, which for modern ENCs is WGS 84.
Position Confidence Starts With the Right Receiver
GNSS and GPS are not competing technologies. GPS is one part of GNSS, and a vessel that uses multiple constellations benefits from greater reliability and availability. For nautical charts, ECDIS solutions, navigation instruments, and bridge publications, contact American Nautical Services at +1 (954) 522-3321 or sales@amnautical.com.
Frequently Asked Questions
Q. What is the difference between GNSS and GPS?
GPS is a single satellite navigation constellation operated by the United States. GNSS is the umbrella term for all satellite navigation systems, including GPS, GLONASS, Galileo, BeiDou, and regional systems. A GNSS receiver uses multiple constellations for better coverage and reliability.
Q. Is GPS part of GNSS?
Yes. GPS is one of the four fully operational global constellations within GNSS. The others are GLONASS (Russia), Galileo (EU), and BeiDou (China).
Q. Why is GNSS better than GPS alone?
GNSS gives a receiver access to more than 100 satellites across multiple constellations, compared to approximately 31 for GPS alone. More satellites improve position accuracy, availability, and redundancy, especially in congested ports, high-latitude waters, or areas with signal obstructions.
Q. Does SOLAS require GNSS on vessels?
SOLAS Chapter V requires all vessels to carry a global navigation satellite system or terrestrial radionavigation receiver to establish and update the ship's position at all times. IMO currently recognizes GPS, GLONASS, BeiDou, Galileo, and NavIC for this purpose.
Q. What GNSS constellations does IMO recognize?
IMO recognizes GPS, GLONASS, BeiDou, Galileo, and the Indian Regional Navigation Satellite System (NavIC) as components of the World-Wide Radionavigation System for maritime use.
Q. Can a GPS receiver also use GNSS?
A GPS-only receiver is limited to the U.S. constellation. A GNSS receiver can use GPS plus other constellations. Most modern maritime receivers are GNSS-capable, even when marketed under the "GPS" label.