Resilient PNT Portal Glossary - Royal Institute of Navigation

Augmentation

Augmentation is the process of enlarging or adding to something. For Resilient Positioning Navigation and Timing purposes, augmentation is taken as adding an additional source of data -an example of this would be providing a system with more precise and more accurate orbital data for each GNSS satellite than the levels of precision and accuracy provided within their own signal broadcasts.

Accuracy

The degree to which the estimated position, speed, or time of a navigation system matches the true value. High accuracy is critical for reliable PNT services, ensuring that positioning information is precise and trustworthy.

ADS-B (Automatic Dependent Surveillance-Broadcast)

A surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling air traffic control and nearby aircraft to receive real-time position information. ADS-B is key for improving airspace safety and efficiency.

AIS (Automatic Identification System)

A tracking system used on ships and by vessel traffic services for identifying and locating vessels. AIS transmits a ship’s position, speed, and other data to avoid collisions and enhance maritime safety.

Almanac

A data file broadcast by GPS satellites containing coarse orbit and status information for all satellites in the constellation. The almanac helps GPS receivers locate satellites quickly and improve time-to-first-fix (TTFF) when obtaining a position.

Altitude

The height of an object or point above a reference level, typically above sea level. In the context of PNT, altitude is an essential component of positioning, especially for aircraft, satellites, and geographic systems. It is commonly measured using altimeters or GNSS systems and is critical for navigation, weather forecasting, and air traffic control.

Bands

Bands are usually referred to in the context of "frequency bands" which are a range of frequencies in the electromagnetic spectrum. All Frequencies in the radio bands(3 Hz-3000GHz) have an International Telecommunications Union (ITU) designator assigned to them. Some frequency bands in the radio Spectrum have an additional alphabetical designation (IEEE Standard 521-2002, the Standard Radar Frequency Letter-band Nomenclature) associated with them . GNSS signals for instance are broadcast in a range of frequencies between 1-2 GHz, which has been designated as a Ultra High Frequency (UHF) signal in the L-band. eLORAN on the other hand transmits in the 90-110 kHz band which does not have an alphabetical designation but is in the Low Frequency (LF )Band.

Beidou

Beidou is a Global Navigation Satellite System(GNSS) constellation owned by the Chinese National Space Agency. It provides full global coverage for PNT data.

Channel

Traditionally this refers to a specific frequency used by a PNT system to transmit or receive signals. In GNSS (Global Navigation Satellite Systems), a channel often refers to the capability of a receiver to track signals from a particular satellite, with more channels enabling better performance and accuracy.

Complementary PNT

Alternative systems or technologies that enhance or back up a traditional or primary PNT service, such as GPS. Complementary PNT solutions help maintain service availability and accuracy when satellite signals are degraded, disrupted, or unavailable.

Constellations

Groups of satellites working together to provide PNT services. Examples include the GPS constellation (U.S.), Galileo (EU), GLONASS (Russia), and BeiDou (China). Each constellation is designed to provide global or regional coverage for reliable positioning and navigation.

Continuity

The ability of a PNT service to operate without unexpected interruptions. High continuity ensures the service remains consistently available, even during periods of environmental interference or system maintenance.

CRPA

A Conformal Radiation Pattern Antenna (also sometimes referred to as a Conformal Reception Pattern Antenna). This is a type of adaptive antenna technology that is used to steer the radiation pattern of the antennas such that nulls in the radiation pattern are created and aligned in the direction of any detected Radio Frequency Interference. Common variants are 4 or 7 channel CRPAs which are used on military platforms such as ships, aircraft and armoured vehicles.

Dead Reckoning

A navigation method that estimates current position based on a known previous position, speed, direction, and time elapsed. Dead reckoning does not rely on external signals, making it useful when GPS or other satellite signals are unavailable, but it can accumulate errors over time without corrections from external references.

Disruption

An event or condition that degrades, interrupts, or denies PNT services, potentially caused by interference, signal obstructions or system failures. Effective resilience strategies help minimise the impact of disruptions on navigation and timing functions.

DME (Distance Measuring Equipment)

A radio navigation technology used in aviation to measure the distance between an aircraft and a ground-based transponder. By calculating the time it takes for a transmitted signal to travel to the ground station and return, DME provides precise distance information for pilots.

DOP (Dilution of Precision)

A measure of the geometry of satellite positions relative to a receiver, affecting the quality and accuracy of GNSS signals. Lower DOP values indicate better satellite geometry and higher positioning accuracy, while higher DOP values suggest degraded accuracy.

Doppler

A shift in the frequency of a signal caused by the relative motion between a transmitter (e.g., satellite) and a receiver (e.g., GNSS device). The Doppler effect can be used to estimate the speed and direction of a moving object, aiding in velocity determination for navigation systems.

eLORAN

Enhanced LORAN is a modernised version of the Low Frequency Long Range (LORAN) Navigation system that was developed by the US in World War II. It is a terrestrial based system that uses a low frequency signal (90-110 Khz) to transmit PNT data. The use of low frequency signals means that eLORAN transmissions are capable of carrying data over large distances and can be received inside buildings or even underground and under shallow water.

Ephemeris

Precise data broadcast by GNSS satellites, detailing their exact position, velocity, and onboard clock errors. The ephemeris information is crucial for receivers to accurately calculate their own position by understanding the location of each satellite at any given moment. It is updated frequently to maintain precision in positioning.

Equator

An imaginary line around the middle of the Earth, equidistant from the North and South Poles, dividing the Earth into the Northern and Southern Hemispheres. The Equator is at 0° latitude and is crucial for geographic coordinate systems. It also plays a key role in defining climate zones and the global navigation reference system.

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Galileo

The European Union’s Global Navigation Satellite System (GNSS), designed to provide highly accurate and reliable PNT services globally. Galileo is intended to be interoperable with other GNSS systems like GPS and GLONASS, offering improved accuracy and availability, especially in urban and challenging environments.

GBAS (Ground-Based Augmentation System)

An aviation system that enhances GNSS signals to provide precise positioning information for aircraft during approaches and landings. GBAS uses ground stations to correct satellite data, improving the accuracy, integrity, and safety of GNSS-based navigation, especially in low-visibility conditions.

GEO (Geostationary Earth Orbit)

A type of satellite orbit where the satellite remains fixed above a specific point on the Earth’s equator, orbiting at an altitude of approximately 35,786 kilometers. GEO satellites are often used for communications and augmentation services, providing consistent coverage over a large area.

GLONASS (Global Navigation Satellite System)

Russia’s GNSS constellation, providing Global PNT services similar to GPS. GLONASS can be used independently or in combination with other GNSS systems, enhancing accuracy and reliability for users worldwide.

GNSS (Global Navigation Satellite System)

A general term for satellite systems that provide PNT services globally. GNSS includes multiple constellations like GPS (U.S.), GLONASS (Russia), Galileo (EU), and BeiDou (China).

GPS (Global Positioning System)

The U.S. GNSS constellation, providing reliable PNT services worldwide. GPS was the first operational GNSS and remains the most widely used, supporting a broad range of civilian and military applications. It consists of a network of satellites that transmit signals to enable precise positioning and timing.

GPWS (Ground Proximity Warning System)

An onboard safety system used in aviation to alert pilots if an aircraft is at risk of unintentional contact with the ground. GPWS uses radar altimeter data to detect terrain proximity and issues warnings to prevent controlled flight into terrain (CFIT) accidents.

HDOP (Horizontal Dilution of Precision)

A specific type of DOP (Dilution of Precision) that measures the impact of satellite geometry on the accuracy of horizontal position estimates (latitude and longitude). Lower HDOP values indicate better satellite positioning and higher horizontal accuracy, while higher HDOP values suggest reduced accuracy due to poor satellite geometry.

ILS (Instrument Landing System)

A precision landing aid used in aviation that provides guidance to aircraft approaching a runway. ILS uses a combination of radio signals (localizer for lateral guidance and glideslope for vertical guidance) to help pilots land safely, especially in poor visibility conditions.

Integrity

The measure of trustworthiness and reliability of PNT information. High integrity ensures that any errors or issues in the PNT system are quickly detected and reported, preventing users from relying on incorrect data. Integrity is crucial for safety-critical applications like aviation and autonomous navigation.

Interference

Any unwanted signal or noise that disrupts or degrades the performance of PNT services. Interference can be unintentional, such as from nearby electronics, or intentional, like jamming. Mitigating interference is essential for ensuring the accuracy and reliability of positioning and navigation systems.

IoT (Internet of Things)

A network of interconnected physical devices embedded with sensors, software, and connectivity features that enable them to collect, exchange, and act on data. In the context of PNT, IoT devices can use GNSS for location tracking and rely on accurate timing for synchronized operations.

IRNSS NavIC (Indian Regional Navigation Satellite System)

India’s regional satellite navigation system, also known as NavIC (Navigation with Indian Constellation). IRNSS NavIC provides accurate PNT services over India and surrounding regions. It consists of a combination of geosynchronous and geostationary satellites, offering both civilian and restricted services.

Jamming

The deliberate transmission of radio frequency signals intended to interfere with or block GNSS and other PNT signals. Jamming disrupts the receiver’s ability to acquire or maintain satellite signals, resulting in degraded or completely denied positioning, navigation, and timing services. Jamming can pose significant risks to safety-critical applications and is often considered a form of electronic attack.

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LEO (Low Earth Orbit)

A satellite orbit that lies relatively close to Earth, typically between 160 and 2,000 kilometres in altitude. LEO satellites are commonly used for communication, Earth observation, and some navigation services. These satellites orbit the Earth much faster than those in higher orbits, providing more frequent coverage of the planet’s surface.

LNAV (Lateral Navigation)

A type of navigation used in aviation and GPS-based systems that provides lateral (horizontal) guidance during flight, typically along predefined flight paths. LNAV helps aircraft navigate safely by following waypoints or routes, especially during the en-route phase of flight. It is often used in conjunction with other navigation systems such as VNAV (Vertical Navigation) for complete guidance.

Meaconing

A form of radio signal interference where a signal is intercepted and retransmitted with a delay, typically to deceive or mislead a receiver about its location. In the context of GNSS, meaconing can cause positioning errors by providing false navigation signals to a receiver.

MEO (Medium Earth Orbit)

A satellite orbit typically between 2,000 and 35,786 kilometers above Earth, where many GNSS satellites operate. MEO satellites offer a balance between the coverage area of GEO satellites and the low latency of LEO satellites, providing global or regional PNT services.

Microsecond

One-millionth of a second.

Millisecond

One-thousandth of a second.

Multipath Interference

A phenomenon where GNSS signals reach a receiver via multiple paths, typically due to reflections from buildings, mountains, or other surfaces. This causes errors in the receiver's position estimation, as the signals arrive at different times and overlap with themselves, which reduces the accuracy of the calculated position.

Nanosecond

One-billionth of a second.

Navigation

The process of planning and/or determining the knowledge of a moving object's position, velocity, and pose over time.

NTP (Network Time Protocol)

A protocol used to synchronise the clocks of computers and network devices over a digital network. NTP ensures that devices maintain accurate time, often to within milliseconds or better, and is commonly used in applications requiring precise timekeeping, such as financial transactions and distributed computing.

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PNT (Positioning, Navigation, and Timing)

A set of technologies and systems used to determine and maintain an object's location, track its movement, and provide accurate timing.

Positioning

The process of determining an object's location relative to some reference frame. It is usual on Earth to position an object using coordinates such as latitude, longitude, and altitude relative to the reference position at Earth’s surface where the equator meets the Primary Meridian.

Pose

A term used to describe the position and orientation of an object in space. In the context of PNT, pose refers to both the geographic location (position) and the angular orientation (e.g., heading, pitch, roll) of an object or device, such as a vehicle or robot.

Precision

The degree to which repeated measurements of the same quantity yield consistent results. High precision in PNT systems means that measurements are highly repeatable, even if they are not necessarily accurate. Precision is essential in applications requiring stable and reliable data, even in the presence of noise or interference.

Prime Meridian

The zero-degree longitude line that runs from the North Pole to the South Pole, passing through the Royal Observatory, Greenwich, in London, England. It serves as the reference point for defining longitude and is used to divide the Earth into Eastern and Western Hemispheres. The Prime Meridian and the Equator together establish the foundation for the world's coordinate system.

PTP (Precision Time Protocol)

A protocol used to synchronise clocks across a network with high precision, typically in the range of nanoseconds to microseconds. PTP is used in systems where accurate time synchronisation is crucial, such as in financial transactions, telecommunications, and distributed systems.

QZSS (Quasi-Zenith Satellite System)

Japan’s regional satellite navigation system, designed to provide highly accurate positioning services, particularly in urban and mountainous areas where GNSS signals may be obstructed. QZSS is compatible with GPS and enhances service availability and accuracy within Japan and surrounding regions.

Reliability

The ability of a PNT system to consistently deliver accurate and usable data over time, without unexpected failures or degradations. A reliable system can maintain performance under a variety of conditions and is essential for applications where continuous, trusted information is critical, such as in aviation or autonomous vehicles.

Resilience

The capacity of a PNT system to maintain its functionality or quickly recover from disruptions, failures, or adversities. Resilient systems are designed to be robust to interference, outages, and other challenges, ensuring continued operation and minimal impact on users.

RNAV (Area Navigation)

A navigation method that allows an aircraft or vessel to navigate along any desired flight path, rather than being restricted to traditional airways or routes. RNAV uses a combination of GPS, inertial navigation, and other systems to enable more flexible and efficient routing.

RN (Route Navigation)

A system or method used to follow a predetermined route or set of waypoints. In aviation and maritime navigation, RN refers to the use of navigation data to stay on course along specific paths, usually defined by airways or maritime lanes.

RNP (Required Navigation Performance)

A standard used in aviation to define the navigation performance required for an aircraft to fly a specific route or procedure. RNP specifies the level of accuracy, integrity, and availability needed for a flight, typically measured in nautical miles (NM). It is used to ensure that aircraft can safely navigate in various airspace conditions, including congested or remote areas, and is a key component of modern air traffic management systems.

SBAS (Satellite-Based Augmentation System)

A system that enhances the accuracy, integrity, and availability of satellite navigation signals, such as those from GPS. SBAS uses ground stations to monitor satellite signals and sends correction messages to improve positioning accuracy, especially in areas where precision is critical, like aviation.

Spoofing

A type of cyber attack in which false GNSS signals are transmitted to deceive a receiver into calculating an incorrect position or timing. Spoofing can mislead navigation systems, causing them to rely on fraudulent data, and is often used to disrupt or manipulate the operation of PNT systems.

TACAN (Tactical Air Navigation)

A military navigation system that provides aircraft with distance and direction information to a ground station. TACAN is similar to civilian DME (Distance Measuring Equipment) but is designed for military use and provides more precise navigation in combat and tactical environments.

TCAS (Traffic Collision Avoidance System)

An aviation safety system that helps prevent mid-air collisions by alerting pilots to nearby aircraft and recommending evasive actions. TCAS uses transponder signals from other aircraft to calculate proximity and issue warnings, improving air traffic safety.

Timing

The measurement and synchronisation of time across systems, essential for various applications including PNT. Accurate timing is crucial in systems like GNSS, telecommunications, and financial transactions, where even small time discrepancies can lead to significant operational issues.

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VNAV (Vertical Navigation)

A navigation system used to provide vertical guidance to aircraft, helping to maintain a safe altitude profile during flight. VNAV works in conjunction with horizontal navigation systems like LNAV (Lateral Navigation) to provide complete, precise guidance along a flight path, including ascent, descent, and level flight.

VOR (VHF Omnidirectional Range)

A type of radio navigation system for aircraft, providing azimuth (directional) information to help pilots navigate to or from a specific location. VOR stations transmit a signal in all directions, allowing aircraft to determine their bearing relative to the station, commonly used for en-route navigation and approach procedures.