Understanding navigation systems via satellites is a study within itself. Throw in acronyms for everything, and you’ve got a whole new language on your hands.
It’s easy to spell out what these acronyms stand for but knowing the context surrounding their differences and how they’re related is much more beneficial when working with different technologies or performing specific tasks. This holds true for GNSS, GPS, and SBAS – three systems with three different meanings and uses.
GNSS: The Genre
Like movies or books, the way satellites are used can be grouped into different categories or applications. GNSS, or global navigation satellite system, is one of these categories. A GNSS is a group of satellites that work together to provide positioning, navigation, and timing (PNT) data for any point on Earth at any given time. This makes a GNSS a type of satellite constellation.
The number of satellites used to create a GNSS can vary, but there are typically over 20 medium Earth orbit (MEO) satellites spread between several orbital planes. This allows for continuous global or near-global coverage no matter where you are.
The quality of a GNSS and the data it collects is evaluated based on accuracy, integrity, continuity, and availability – four unique characteristics of the received information:
- Accuracy: The difference between a measured and real position, speed, or time
- Integrity: The system’s capacity to be accurate
- Continuity: The system’s ability to continually function
- Availability: How often the above criteria are optimal
GNSS were primarily used for the purpose of military operations, helping forces be more precise with their attacks and helping them locate themselves more easily when on unfamiliar terrain. This means that in terms of the development of GNSS, countries or entities that have placed focus on strengthening their military forces have had reason to create their own.
Examples of GNSS include:
- GPS (Global Positioning System) owned and operated by the United States
- BDS (BeiDou Navigation Satellite System) owned and operated by the People’s Republic of China
- Galileo owned and operated by the European Union
- GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema) owned and operated by Russia
Other applications for GNSS in addition to military operations include transportation (air, boats, cars, cyclists, etc.), precision agriculture, surveying, GIS, archaeology, geology, and truly any other activity where location is necessary to complete a task.
GPS: The Starring Role
Of the GNSS that exist, GPS is the most prevalent one used. With 32 MEO satellites on six different orbital planes, it’s the world’s most utilized satellite navigation system.
Developed by the US Department of Defence in the 1970s, GPS was originally known as NAVSTAR (Navigation Satellite Timing and Ranging). Though built with the intention of allowing everyday users to access the PNT data received, GPS was built with what’s called selective availability – an intentional degradation of data to publicly available navigation signals. This meant that anyone outside of the US military using GPS would receive data that could be up to 100m off. The intention of selective availability was to ensure military opposition would not be able to accurately position themselves or navigate efficiently or effectively, thereby giving the US military an upper hand.
As of May 2000, selective availability was turned off and the US has no intent on ever turning it on again. And it’s for this reason that you probably access and utilize GPS data on a near-daily basis.
SBAS: The Supporting Actor
Though GPS data points and those collected from other GNSS are representatives of real locations on Earth, they aren’t always entirely accurate. To correct for any inaccuracies, a satellite-based augmentation system (SBAS) is used. Like a supporting actor, it’s something that’s always there but doesn’t always get the recognition it deserves for the role it plays.
Here’s how an SBAS works. Before you receive navigational data from GPS satellites, the signal is first received by a ground station to QA/QC your data (aka. process and correct it). The corrected measurements are then sent to SBAS satellites and then sent to a GPS receiver that a person has in their hand or vehicle. The reason the corrected data is sent back to satellites rather than directly to your receiver is that if it was sent from a ground station, it would only be able to reach receivers that are relatively close by. Sending the information back to satellites allows information to be received throughout broader areas, no matter where a ground station may be.
There are many SBAS utilized around the world including:
- WAAS (Wide Area Augmentation System) operated by the USA
- EGNOS (European Geostationary Navigation Overlay Service) operated by the EU
- MSAS (Michibiki Satellite Augmentation System) operated by Japan
- GAGAN (GPS-aided GEO-Augmented Navigation) operated by India
Other SBAS that are currently being developed include:
- BDSBAS (BeiDou SBAS) operated by the People’s Republic of China
- KASS (Korea Augmentation Satellite System) operated by South Korea
- SDCM (System for Differential Corrections and Monitoring) operated by Russia
- SouthPAN (Southern Positioning Augmentation Network) operated by Australia and New Zealand
Putting it All Together
When it comes to utilizing the data and information obtained from a GNSS, like GPS, which has been corrected by an SBAS, a receiver is used. Receivers are chips or devices that receive satellite signals to provide users with navigational information. So, yes. Your cell phone has a GPS receiver built into it!
Other devices that work with GPS are handheld devices, like the ones you may use for surveying or hiking, or mounted, like the ones you may use in your vehicle. These are the most common civilian uses of GPS, though GPS is still used for military and aviation purposes.
Receiving this data not only allows you to navigate through built-in software or apps like Google Maps, but you can also share your location information, too. For many apps out there, the ability to share location has been a major feature that provides improved user experience. Whether it’s “dropping your location” or attaching a location to a photo, you’ve got GPS (with the help of SBAS) to thank for it.
Other GNSS like Galileo are being further developed to be accessible by the everyday person like GPS is. In addition to the public being provided with access to more location information and data, more GNSS and SBAS will continue to be developed.
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