science

GNSS augmentation

GNSS augmentation is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand GNSS augmentation rather than just read about it. In short: GNSS augmentation is a method of improving the satellite navigation system's attributes, such as precision, reliability, and availability, through the integration of external information into the calculation process. There are many such systems in place, and they are generally named or described based on how the GNSS sensor receives the external information.

Key takeaways

GNSS augmentation belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GNSS augmentation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GNSS augmentation from memory before moving on to harder problems.

Reference excerpt

GNSS augmentation is a method of improving the satellite navigation system's attributes, such as precision, reliability, and availability, through the integration of external information into the calculation process. There are many such systems in place, and they are generally named or described based on how the GNSS sensor receives the external information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay; "state-space representation"), others provide direct measurements of how much the signal was off in the past (differential GPS; "observation-space representation"), while a third group provides additional vehicle information to be integrated in the calculation process (sensor fusion).

Satellite-based augmentation system

Satellite-based augmentation systems (SBAS) support wide-area or regional augmentation through the use of additional satellite-broadcast messages. ICAO material describes SBAS as a wide-coverage GNSS augmentation system in which the user receives correction and integrity information from a satellite-based transmitter, with Standards and Recommended Practices (SARPs) for SBAS included in Annex 10. This Annex describes a standard data format for use in aviation as well as their broadcast on L1 (and more recently L5). Many SBAS satellites also provide their own timing/ranging signals, acting as additional satellites for positioning. Using measurements from the ground stations, state-space correction messages are created and sent to one or more satellites for broadcast to end users as differential signal. These correction messages include separate values for location-independent corrections (satellite clock, ephemeris, health, etc.) and location-dependent corrections (ionospheric delay). The idea of SBAS was first proposed in 1991 as "wide-area differential GPS" (WADGPS), but unlike typical DGPS, WADGPS and many later SBAS implementations provide state-space as opposed to observation-space corrections consisting of location or pseudorange errors at specific stations. Current and upcoming SBAS systems implementing the aviation standard (ICAO) state-space format include:

The Wide Area Augmentation System (WAAS), operated by the United States Federal Aviation Administration (FAA). The European Geostationary Navigation Overlay Service (EGNOS), operated by the ESSP (on behalf of EU's GSA). The Multi-functional Satellite Augmentation System (MSAS), operated by Japan's Ministry of Land, Infrastructure and Transport Japan Civil Aviation Bureau (JCAB). Since 2020, MSAS operates as a service of QZSS (L1Sb). The GPS-Aided GEO Augmented Navigation (GAGAN), operated by the Airports Authority of India. The BeiDou Satellite-based Augmentation System (BDSBAS-B1c) operated by China. The System for Differential Corrections and Monitoring (SDCM), operated by Russia's Roscosmos based on GLONASS. The Southern Positioning Augmentation Network (SouthPAN), developed by Australia and New Zealand, with initial services going live in September 2022. The Korea Augmentation Satellite System (KASS) (Republic of Korea), under development as of 2021. The SBAS for Africa and Indian Ocean (A-SBAS) (ASECNA), under development as of 2021. Additional current SBAS systems include:

The Galileo High Accuracy Service (HAS), a separate state-space service for Precise Point Positioning directly broadcast by Galileo satellites (E6) The Quasi-Zenith Satellite System (QZSS), operated by Japan, started initial operations in November 2018. Its SBAS services are known as SLAS (an observation-space, pseudorange correction service, L1S), CLAS, and MADOCA-PPP (both state-space services, L6D and L6E). QZSS also operates in a non-SBAS mode called PNT, essentially acting as extra GNSS satellites. The Chinese BeiDou system has an observation-space service and a state-space PPP service (PPP-B2b). The commercial StarFire navigation system, operated by John Deere and C-Nav Positioning Solutions (by Oceaneering International). The commercial Starfix DGPS System and OmniSTAR system, operated by Fugro. The commercial Atlas GNSS Global L-Band Correction Service system, operated by Hemisphere GNSS. The Australian SBAS using the Inmarsat 4F1 geostationary satellite, which suffered an outage in April 2023. Defunct SBAS include:

The Wide Area GPS Enhancement (WAGE), operated by the United States Department of Defense for use by military and authorized receivers. The GPS·C, short for GPS Correction, was a differential GPS data source for most of Canada, maintained by the Canadian Active Control System, part of Natural Resources Canada – now decommissioned.

Internet-based augmentation A few online services provide access to the data broadcast by SBAS satellites via the Internet, which is useful in areas of low SBAS visibility (e.g. unmanned aerial vehicles navigating urban canyons). Some services such as International GNSS Service (IGS) provide direct access to predicted orbit and clock corrections for GPS (covering a couple of hours). Networked Transport of RTCM via Internet Protocol is an internet protocol for access to such data. NASA operates the Global Differential GPS (GDGPS) system, using data from many ground stations located worldwide. GDGPS disseminates real-time orbit and clock corrections and supports a wide range of GNSS networks beyond GPS (GLONASS, BeiDou, Galileo, and QZSS). WAAS is based on correction data from GDGPS. GDGPS is commonly used to generate assisted GNSS data. Ground stations are commonly used to accumulate continuous GNSS observations to achieve post-hoc correction of data to the centimeter level. Two example systems are the US Continuously Operating Reference Stations (CORS) and the International GNSS Service (IGS).

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with GNSS augmentation

Start with the simplest possible case. Write down what GNSS augmentation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to GNSS augmentation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about GNSS augmentation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of GNSS augmentation

In research: GNSS augmentation appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses GNSS augmentation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: GNSS augmentation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Satellite-based augmentation systems, Satellite navigation, so understanding it makes those chapters shorter.
In everyday life: Look for GNSS augmentation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study GNSS augmentation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GNSS augmentation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain GNSS augmentation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GNSS augmentation in simple terms?

Why does GNSS augmentation matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study GNSS augmentation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on GNSS augmentation.