Global Navigation Satellite System

What is GNSS?

A Global Navigation Satellite System, or GNSS, is a network of satellites that broadcasts timing and orbital information, which is used for navigation and measuring the position of an item. In Windward’s context, GNSS is used to determine the location of a vessel. 

GNSS measures three things. The location of an item, the speed of an item, and timing. With the right technology in place, it is extremely accurate. 

  • Location – accurate within millimeters 
  • Speed – User range rate error (URRE) of ≤0.006 m/sec over any 3-second period
  • Timing – ≤30 nanoseconds (billionths of a second)

How Does GNSS work?

Three elements comprise GNSS systems. The space segment refers to the network of satellites, called constellations, that orbit 20,000 kilometers above the earth. Each satellite in the GNSS constellation sends out a signal that identifies it and shares its time, orbit, and status. 

The second element of GNSS is the control segment, powered by an earth-based network of ground control stations that function as GNSS receivers. The ground control stations analyze the signals they receive and transmit orbit and time corrections to the satellites in the constellation through data uploading stations. 

The third element of GNSS is the user segment. This refers to the device, such as a smartphone or receiver, that is implanted on the vessel being tracked. 

What is the Difference between GNSS & GPS?

People are often confused between GNSS vs. GPS, as both appear to be global tracking systems that can identify an object’s location. 

GNSS is a broad term for a satellite navigation system that identifies the position, navigation, and timing used in different applications. GPS is the name of the North American GNSS system.

What is GNSS Manipulation?

According to Global Trade Review, “illicit actors are turning to new techniques to evade sanctions on maritime trade, with industry insiders warning of a spike in location signal manipulation and “deep” dark activity.” GNSS manipulation or location tampering is the use of a machine-generated location/path to disguise the true location of the vessel. Multiple methods have been identified to carry out this deception, including false transmission onboard the vessel and third-party onshore accomplices. It’s critical to “know your vessel”, and understand your risk and exposure.

How are GNSS Systems Measured? 

There are four criteria used when measuring GNSS data to determine the performance of the system. 

  • Accuracy – the difference between the GNSS receiver’s measured position, speed, and time, and the object’s actual position, speed, and time. 
  • Availability – the percentage of time the GNSS is available.
  • Continuity – the system’s ability to perform its required function throughout an operation, without interruption.
  • Integrity – the measure of trust users can place in the GNSS data. This includes the system’s ability to warn users when the system is not functioning correctly.

What are Factors that Impact GNSS Accuracy?

GNSS is a highly accurate positioning system. Depending on the quality of the device and other environmental factors, GNSS can locate an item within a few centimeters. The highest accuracy occurs with dual-frequency GNSS receivers or augmentation systems beneath an open sky. A typical smartphone, in contrast, offers accuracy within a 5-meter radius. 

Factors that reduce GNSS accuracy:

  • Signal blockage due to buildings, bridges, and trees
  • Underground, or indoor use
  • Signal reflected off the sides of buildings
  • Major solar storms
  • Satellite maintenance

Additionally, sometimes GNSS measurements are accurate, but incorrectly drawn maps, missing roads, mislabeled businesses, or mistakenly labeled street addresses make them seem incorrect.

What are the Different GNSS Systems Being Used?

Currently, there are four main GNSS constellations and two regional ones in use. 

  • Global Positioning System (GPS), United States – the first GNSS system in the world, GPS initiated operations in 1978 and has been available for global use since 1994. GPS has 31 satellites in its constellation that are in orbit and operational. It is maintained by the United States Air Force.
  • Global Navigation Satellite System (GLONASS), Russia – Russia’s GNSS constellation began flight tests in 1982 and went operational in 1993, with 12 satellites in two orbits. Today, there are 26 satellites in the GLONASS constellation, which is operated by the Russian Aerospace Defence Forces.
  • Galileo, European Union – the European Union’s Galileo system was developed by the European Space Agency and is currently operated by the European Space Agency (ESA) for the Space Programme (EUSPA). Galileo went operational in 2016 and currently has 24 active satellites and two base stations. 
  • BeiDou Navigation Satellite System (BDS), China – BeiDou first went operational as a regional system with limited coverage in 2000. Since then, it has expanded its operations and has provided global coverage since 2018. China has reportedly launched 55 satellites as part of different BDS constellations, of which 35 are believed to still be operational. 
  • Indian Regional Navigation Satellite System (IRNSS), India – tThe IRNSS constellation first began orbiting in 2018. There are currently seven satellites in the constellation. Its coverage area includes India and 1,500 km around the country. NavIC, the operational arm of the IRNSS, offers a standard level of service for civilian use and an encrypted service for authorized users. 
  • Quasi-Zenith Satellite System (QZSS), Japan – the QZSS is a regional GNSS covering Asia-Oceanic regions. The system has four satellites in its constellation and has been operational since November 2018. 

GNSS Applications

There are a number of GNSS applications used in military, commercial, and private settings. These include navigation systems, tracking, scientific research, telecommunications, emergency response, and more. GNSS is even used by dog owners to ensure that pets don’t get lost. 

Interesting GNSS Facts

Selective Availability

In 1983, U.S. President Ronald Reagan told civilians they could use the service. However, in an effort to secure a military advantage for the United States, he limited its accuracy with a feature called “Selective Availability.”  

Selective Availability was an intentional degradation of GPS. Rather than providing accurate locations, civilian GPS was accurate within 50 meters. 

With the advent of new technologies, Bill Clinton eliminated the use of Selective Availability in May 2000. Today, GPS is accurate for civilian use. 

Development of the IRNSS

India decided to develop its own regional service in 1999 after the United States denied its request to use its GPS for military use in the Kargil region.