Global Navigation Satellite Systems (GNSS) are the receivers that utilize different systems like GPS, GLONASS, Galileo, and BeiDou. These systems provide accurate positioning and timing information to users worldwide. This article describes major sectors of civil GNSS Applications. 

GNSS Applications

The major sectors in Civil GNSS Applications are: 

• Surveying 
• Mapping 
• Marine 
• Aviation
• Land Navigation
• Military 
• Space 

GNSS technology is used to determine the location of points on Earth's surface. It includes the process called trilateration. In this process, it receives signals from multiple satellites simultaneously, so that, the surveyors can calculate the exact location. It also involves measuring the distance between satellites and receivers to determine the position in 3D space. 

Surveying & Mapping

1. A cadastral survey aims to establish property boundaries. Fiscal policies such as land taxation rely heavily on cadastral surveying.

2. Construction surveying covers the different construction stages of a building or civil engineering project, whereas machine control applications automate construction activities: 

• Machine control applications use GNSS positioning, for example, to automatically control the blades and buckets of construction equipment using information provided by three-dimensional (3-D) digital design.
• Person-based applications enable many positioning tasks, including making surveys, checking levels, performing built checks, and staking out reference points and markers. 
• In mapping, GNSS is used to define specific location points of interest for cartographic, environmental, and urban planning purposes.
•  Mine surveying involves measurements and calculations at each stage of mine exploitation, including a safety check.
• Marine surveying encompasses a wide range of activities (seabed exploration, tide and current estimation, offshore surveying, and so forth), all of whose outcomes are important for maritime navigation.
  
  

Marine Navigation 

Even submarines can use GNSS whenever they can get their antennas close to or above the surface. Since the early 1980s, sea-level users need only three satellites in view to get a two-dimensional fix; GPS has been used to fix positions on the ocean. Today the market is mature. Along with radios and radar, a GNSS receiver is a piece of standard equipment on any boat operating far from shore. Most can obtain differential corrections from an SBAS. Many others use corrections provided by a radio beacon-based system (e.g., the NDGPS) if available.

The above figure shows a marine navigator with database management capability and graphical display of position and speed information. 

Fisheries management is a worldwide mandate requiring swift action by governments when a sea boundary is intruded upon. Dwindling fish stocks have prompted the establishment of strict guidelines for fishermen and the closure of entire grounds. The situation is also making countries that share sea boundaries more sensitive to foreign fishing in their waters. These tensions engender the need for accurate position determination and recording to prove or disprove a boundary violation, particularly in the South China Sea.

NSS can aid in the berthing and docking of large vessels, by means of position, attitude, and heading reference systems (PAHRS). These installations use multiple antennas aboard the vessel along with DGNSS corrections to determine an accurate representation of the ship’s orientation and position. Combined with appropriate reference cartography, this can be an immense aid in the handling of large vessels in close quarters. Vessels worldwide are candidates for this type of system.

Recreational vessels make good use of basic GNSS for navigation, and the acceptance of differential GNSS bodes well for the health of that sector. The huge number of vessels and the value of GNSS in marine navigation, fishing, and water way maintenance, coupled with strong economic activity, will allow steady growth to a level of near $1.1 billion by 2020.

Air Navigation

The big need for navigation by GNSS was primarily for over-ocean operations where there were no VHF Omnidirectional Range/Distance Measuring Equipment 14.2 Civil Applications of GNSS 931 (VOR/DME) stations and in parts of the world where radio NAVAIDS were sparse and primitive.

NSS could be applied to all phases of flight operations if only its accuracy, integrity, and continuity of service could be assured to the acceptable levels demanded for safety-of-life applications. However, introducing GPS into the U.S. national airspace caused some major issues. Over the United States, the en-route VOR/DME system was adequate at least until the traffic load swamped the Air Traffic Management (ATM) system. Nonetheless, with GPS, aircraft would not have to stay on these fixed highways and thus could fly great circle routes and/or optimum fuel consumption routes. Capacity limitations of the present system and skyrocketing fuel costs eventually overcame airlines’ resistance to new equipment installations as long as the cost-benefit of using GPS could be shown to be positive.

Many airlines routinely check on their aircraft in flight. Those equipped with GNSS can accurately report their position. Overbroad ocean areas, they must utilize a leased communications satellite channel. One airline that did not choose to enter into such a lease was Malaysia Air, resulting in a lack of location information when one of its aircraft disappeared over the Indian Ocean in 2014. While the incident may not have been preventable, at least the area of the search for the aircraft should have been much smaller. China’s Civil Aviation Administration has announced that they will be testing a tracking system for general aviation aircraft and then cargo and passenger aircraft with BeiDou.

Land Navigation 

Here, for land navigation, railways is taken as an example.

•  High-density command and control systems assist train command and control on main lines, referring primarily to the European Train Control System (ETCS) in Europe and some regions in the rest of the world, as well as positive train control (PTC) in North America. GNSS can also be a source of additional input (e.g., for enhanced odometry in ETCS or to support PTC).
•  Low-density line command and control systems provide full signaling capabilities supported by GNSS on lines with small to medium traffic. These lines are usually located in rural areas, where cost savings can be vital for the viability of a service.
•  Asset management includes such functions as fleet management, need-based maintenance, infrastructure charges, and intermodal transfers. GNSS is increasingly seen as a standard source of positioning and timing information in these systems.
•  Passenger information systems on-board trains show the real-time location of a train along its route. Increasingly, the GNSS location of a train is also supporting platform and online passenger information services.

Space Applications

•  Navigation solutions—providing high precision orbit determination, and minimum ground control crews, with existing space-qualified GPS units. 
• Attitude solutions—replacing high-cost on-board attitude sensors with low-cost multiple GPS antennae and specialized algorithms.
•  Timing solutions—replacing expensive spacecraft atomic clocks with low-cost, precise time GPS receivers. 
• Constellation control—providing a single point-of-contact to control for the orbit maintenance of large numbers of space vehicles such as telecommunication satellites. 
• Formation flying—allowing precision satellite formations with minimal intervention from ground crews. 
• Virtual platforms—providing automatic “station-keeping” and relative position services for advanced science tracking maneuvers such as interferometry. 
• Launch vehicle tracking—replacing or augmenting tracking radars with higher precision, lower-cost GPS units for range safety and autonomous flight termination.

Military Applications 

GPS and GLONASS were designed to satisfy the military requirements for worldwide PNT requirements. Only satellite-based systems could ensure continuous global coverage. The signals had to enable very accurate fixes yet be resistant to enemy jamming. Thus, both the United States and Russia developed user receivers that relied on their own signal called the P-code. 

• Some typical receivers were produced for aircraft first in a standard avionics package known as a 3/4 Air Transport Rack (ATR) size (Rockwell-Collins 3A) shrinking its width in half later to a 3/8 ATR [Rockwell-Collins and Raytheon Miniature Airborne GPS Receiver (MAGR)].

Note: 

All the Content is taken from the reference of Elliot D Kaplan and Christopher J Hegarty, “Understanding GPS principles and applications”, Artech House Publishers, 2/e Boston & London 2005.