Introduction to GNSS (1)
- 1. Center for Research and Application for Satellite Remote Sensing Yamaguchi University Introduction to GNSS (1)
- 2. • GNSS means Global Navigation Satellite System • Refers to a constellation of satellites providing signals from space that transmit positioning and timing data to GNSS receivers. • By definition, GNSS provides global coverage. • Examples of GNSS include Europe’s Galileo, the USA’s NAVSTAR Global Positioning System (GPS), Russia’s Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) and China’s BeiDou Navigation Satellite System. https://www.gsa.europa.eu/european-gnss/what-gnss GNSS
- 3. To improve the performance of the GNSS, some countries launch RNSS: • Indian Regional Navigation Satellite System: Navigation with Indian Constellation (IRNSS: NavIC) • Quasi-Zenith Satellite System (Japan) Satellite-based Augmentation System (SBAS) • The Wide Area Augmentation System (WAAS), USA • The European Geostationary Navigation Overlay Service (EGNOS), Europe • The Multi-functional Satellite Augmentation System (MSAS), Japan • The Quasi-Zenith Satellite System (QZSS), Japan • The GPS Aided Geo Augmented Navigation (GAGAN), India • The GLONASS (System for Differential Correction and Monitoring, SDCM), Russia with global coverage. • The Satellite Navigation Augmentation System (SNAS), proposed by China Regional Navigation Satellite System (RNSS) and Augmentation System
- 4. • US.-owned utility that provides users with positioning, navigation, and timing (PNT) services. • Maintains availability of at least 24 operational GPS satellites, 95% of the time. • 31 operational GPS satellites (as of April 24, 2019) • Flies in medium earth orbit (MEO) at an altitude of approximately 20,200 km (12,550 miles) at 55⁰ inclination • Each satellite circles the Earth twice a day. • There are six equally-spaced orbital planes with four "slots" occupied by baseline satellites. • This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet. https://www.gps.gov/systems/gps/ GPS
- 5. • Owned and operated by the People's Republic of China. • 20 satellites (to date)had been launched • 30 satellites by around 2020. • Characteristics: • Hybrid constellation consisting of satellites in 3 kinds of orbits (GEO, IGSO, MEO) • More satellites in high orbits • Multiple frequencies • Integrates navigation and communication capabilities for the first time • 5 major functions – real-time navigation, rapid positioning, precise timing, location reporting and short message communication services. http://en.beidou.gov.cn/ BeiDou Navigation Satellite System (BDS)
- 6. • Europe owned under civilian control • 24 operational satellites plus 6 in-orbit spares • 3 circular MEO planes at 23 222 km altitude at 56⁰ inclination • 4 carriers: E5a (1176.45 MHz), E5b (1191.795 MHz), E6 (1278.75 MHz) and E2-L1-E1 (1575.42 MHz) • Provides a global Search and Rescue (SAR) function. Satellites are equipped with a transponder, which is able to transfer the distress signals from the user transmitters to regional rescue co-ordination centers, which will then initiate the rescue operation. • At the same time, the system will send a response signal to the user, informing him that his situation has been detected and that help is on the way. http://www.esa.int Galileo
- 7. • Owned and operated by Russia • consists of 24 satellites equally distributed in 3 orbital planes inclined at 64.8° to the equator with nominal altitude of 19,100 km and an orbital period of 11 hours, 15 minutes, 44 seconds. • Better suited for usage in the Northern Hemisphere than in the Southern Hemisphere, due to a higher number of ground stations in these locations • Differences with GPS • Satellites motion is described using fundamentally different mathematical models • With GPS, satellites use the same radio frequencies but have different codes for communication, while GLONASS satellites have the same codes but use different frequencies, allowing satellites on the same orbital plane to communicate with one another. https://www.glonass-iac.ru/en GLONASS
- 8. • Independent regional navigation satellite system being developed by India. • Primary service: India and 1500 km from its boundary. • Extended Service Area: Lat: 30⁰ S - 50 deg ⁰ N, Lon: 30⁰ - 130⁰ E • 8 satellites – 3 GEO and 5 geosynchronous orbits inclined at 29⁰ from the equator in 2 different planes. IRNSS:NaVIC
- 9. • QZSS is a regional system owned by the Government of Japan and operated by QZS System Service Inc. (QSS). • Composed mainly of satellites in quasi-zenith orbits (QZO) • QZSS complements GPS to improve coverage in East Asia and Oceania. • To have an operational constellation of 4 satellites by 2018 and expand it to 7 satellites for autonomous capability by 2023. QZSS
- 10. • The International Telecommunications Union (ITU) between 1559 MHz and 1610 MHz and designated as Radio Navigation Satellite Service (space-to-earth) (RNSS s-e). • GPS signals between 1560 MHz and 1590 MHz. • This same spectrum is also shared by other Global Navigation Satellite System (GNSS) service providers and their space-based augmentation services. • The Russian GLONASS operates in the upper end of the RNSS band between 1590 MHz and 1610 MHz. Allocated bands required to operate
- 12. • Space segment – consists of satellite constellations • Control segment - consists of a global network of ground facilities that track the satellites, monitor their transmissions, perform analyses, and send commands and data to the constellation • User segment – includes the equipment and the persons who receive the signals Segments
- 13. Space segment
- 15. User segment
- 16. • High Earth Orbit (HEO) ≥ 35, 780 km • Medium Earth Orbit (MEO) 2,000 to 35,780 km • Low Earth Orbit (LEO) 180-2,000 km https://earthobservatory.nasa.gov/features/OrbitsCatalog Orbits
- 17. Inclination is the angle of the orbit in relation to Earth’s equator. A satellite that orbits directly above the equator has zero inclination. If a satellite orbits from the north pole (geographic, not magnetic) to the south pole, its inclination is 90 degrees. Inclined orbit
- 18. Geosynchronous – its orbit matches Earth’s rotation. The satellite seems to stay in place over a single longitude, though it may drift north to south (orbit may be inclined e.g. Inclined Geosynchronous Orbit, IGSO) Geostationary – a geosynchronous orbit where the satellite is directly over the equator (eccentricity and inclination at zero). Satellites are placed in HEO to match Earth’s orbit HEO
- 19. • Satellites in a medium Earth orbit move more quickly. • 2 medium Earth orbits: 1) semi-synchronous orbit and 2) Molniya orbit. • Semi-synchronous orbit: • near-circular orbit (low eccentricity) about 20,200 kilometers above the earth’s surface. • takes 12 hours to complete an orbit. In 24-hours, the satellite crosses over the same two spots on the equator every day. • consistent and highly predictable. • orbit used by many navigation satellites • Molniya orbit: • invented by the Russians • works well for observing high latitudes The Molniya orbit combines high inclination (63.4°) with high eccentricity (0.722) to maximize viewing time over high latitudes. Each orbit lasts 12 hours, so the slow, high- altitude portion of the orbit repeats over the same location every day and night. MEO
- 20. • Most scientific satellites and many weather satellites are in a nearly circular, low Earth orbit. A Sun-synchronous orbit crosses over the equator at approximately the same local time each day (and night). This orbit allows consistent scientific observations with the angle between the Sun and the Earth’s surface remaining relatively constant. LEO
- 21. • Coordinate Systems are the central mathematical element of any geodetic reference system. • definition of its origin (3 elements), • orientation of the axes (3 elements), • scale Orthonormal base vectors and the same scale along all three axes. Coordinate System
- 22. • Space-fixed or inertial systems, in which the positions of stars are fixed or almost fixed and in which the motion of artificial satellites can be formulated according to the Newtonian laws of mechanics. • Earth-fixed systems, in which all terrestrial points can be expressed conveniently as well as vehicles in motion on the earth's surface. • Local horizon systems, fixed to observatories or instruments and often oriented horizontally with one axis pointing towards north. 3 levels of coordinate systems
- 23. http://mediatum.ub.tum.de/doc/1367021/714162.pdf Orbital orientation in a space-fixed coordinate system
- 24. • Reference system consists of: • adopted coordinate system • a set of constants (e.g. constants of a reference ellipsoid), models and parameters (e.g. parameters of a reference gravity field) • Reference frame contains all elements required for the materialization of a reference system in real world. WGS 84 constants Earth-fixed reference system
- 25. • Earth-Centered, Earth- Fixed • ECEF rotates with the earth hence the coordinates of a point fixed on the surface of the earth does not change. ECEF (Geocentric Reference System)
- 26. • The GNSS satellites orbit around the center of mass of the earth. • They have no concept of where the surface of the earth is. • The GNSS receiver, which is on the surface of the earth, is just as well be in outer space as far as the GPS coordinate or Earth-Centered-Earth- Fixed XYZ is concerned. • The microcomputer in the receiver converts these XYZ to latitude, longitude and ellipsoidal height. XYZ to Latitude, Longitude and height
- 27. The orbits of two GPS satellites in a space-fixed geocentric coordinate system The orbits of two satellites in an earth- fixed geocentric coordinate system Orbits of Satellites
- 28. Ground track of GPS SV 10
- 29. • “Parametry Zemli 1990”(PZ-90.11) - reference system for geodetic support of orbital missions and navigation of the Government of Russia. Needs transformation parameters to align with WGS 84/ITRS. • International Terrestrial Reference System (ITRS) - maintained by the International Earth Rotation Service (IERS), which monitors the Earth's orientation parameters for the scientific community through a global network of observing stations. • World Geodetic System of 1984 (WGS 84) - reference system for the Global Positioning System (GPS). It is compatible with the International Terrestrial Reference System (ITRS) • Galileo Terrestrial Reference Frame (GTRF) - an independent realization of the international terrestrial reference system (ITRS). GNSS Geocentric Reference Systems
- 30. Satellite gravimetry (measurement of gravity) Satellite Altimetry (measurement of global sea level) Very Long baseline interferometry (VLBI) (high precision and long term stability) Satellite Laser Ranging (SLR) (long term stability and geo-centricity) Lunar laser ranging (LLR) (geo-centricity, long term stability, relativistic effects) The French tracking system DORIS (Doppler Ortbitography and Radiopositioning Integrated by Satellite) The Global Navigation Satellite System Space techniques that are contributing to the determination of reference system
- 31. • TIME is the most important element in GNSS • Coordinated Universal Time (UTC) is the basis for civil time today. This 24-hour time standard is kept using highly precise atomic clocks combined with the Earth's rotation. • 2 components are used to determine UTC • International Atomic Time (TAI): A time scale that combines the output of some 200 highly precise atomic clocks worldwide and provides the exact speed for our clocks to tick. • Universal Time (UT1), also known as Astronomical Time, refers to the Earth's rotation around its own axis, which determines the length of a day. • The International System of Units (SI) defines one second as the time it takes a Cesium-133 atom at the ground state to oscillate exactly 9,192,631,770 times. https://www.timeanddate.com/time/leapseconds.html Time System
- 32. • Leap seconds are added to (UTC) – and clocks worldwide • The reason is that the velocity of Earth's rotation around its own axis does not match the speed of atomic time. • Atomic clocks deviate only 1 second in up to 100 million years. • Atomic clock is more precise than Earth Leap Second
- 33. • GPS Time (GPST) GPS Time • is a continuous time scale (no leap seconds) • starts at 0h UTC of January 6, 1980 • At that epoch, TAI was ahead by 19 seconds. • GPS time is synchronised with the UTC (USNO) at 1 microsecond level (modulo one second), but actually is kept within 25 ns • TOW (Time of Week)-GPS week 0 (zero) began at the 0h UTC of January 6, 1980 • SOW (Seconds of Week) starting at 0h of Sunday • Week roll over on August 1, 1999 and April 6, 2019 (10-bit binary limits week number to 1024 weeks) https://gssc.esa.int/navipedia/index.php/Time_References_in_GNSS GNSS Time Systems
- 34. •GLONASS Time (GLONASST) • generated by the GLONASS Central Synchroniser • and the difference between the UTC (SU)GLONASST should not exceed 1 millisecond plus three hours (i.e., GLONASST=UTC(SU)+3h−τ , where |τ|<1milisec.), but τ is typically better than 1 microsecond. • Note: Unlike GPS, Galileo or BeiDou, GLONASS time scale implements leap seconds, like UTC GNSS Time Systems
- 35. • Galileo System Time (GST) • a continuous time scale maintained by the Galileo Central Segment and synchronised with TAI with a nominal offset below 50 ns. • The GST start epoch is 0h UTC on Sunday, 22 August 1999. • BeiDou Time (BDT) • a continuous time scale starting at 0h UTC on January 1, 2006 and is synchronised with UTC within 100 ns< (modulo one second) Atomic clock on board Galileo satellite GNSS Time Systems
- 36. • Why is geoid important in GNSS positioning? “The earth is not a perfect ellipsoid. It has mountains, craters, and other features above or below the mathematically perfect ellipsoidal reference. That’s why you could take a GPS receiver on a boating dock at “sea level” and capture a — perfectly accurate — ellipsoidal height of -20 meters. But a dock isn’t 20 meters under water (or you would have bigger issues than interpreting your GPS receiver). So, although your GPS receiver’s ellipsoidal reading is accurate, it doesn’t seem to make sense”. -https://eos-gnss.com/elevation-for-beginners • Therefore, users must transform their ellipsoidal height into a practical elevation reference. The Geoid (Earth Gravity Model)
- 37. • A reference ellipsoid may be above or below the surface of the earth • If the ellipsoid’s surface is below the surface of the earth, h is positive; • if the ellipsoid’s surface is above the surface of the earth at the point, h is negative (e.g. Dead Sea Region and parts of Canada) Ellipsoidal height (h)
- 38. • The geoid is completely defined by gravity • It is lumpy, because gravity is not consistent across the surface of the earth • The geoid is an equipotential surface that approximates (or fits in the least squares sense) the mean sea level ⚫The geoid height or geoid undulation designated by N, is the height from the surface of an ellipsoid to the geoid. ⚫The separation between the geoid and the smooth ellipsoid worldwide varies from about +85 meters west of Ireland to about -106 meters in the area south of India near Sri Lanka. https://www.e-education.psu.edu/geog862/node/1820 Geoid height (N)
- 39. Formula for conversion: H = h – N where: H Orthometric Height Elevation approximating the mean sea level h Ellipsoidal Height Elevation above or below the reference ellipsoid from GPS receiver N Geoid Height Offset between the geoid and ellipsoid references; we find N in the geoid model used Example: h = 100 meters N = -25 meters Therefore, H = (100 meters) – (-25 meters)= 125 meters Converting h to orthometric height (H)
- 40. • Global gravity or geoid models can be found in http://icgem.gfz-potsdam.de • Japanese Geoid 2011 (Ver.2.1) released on February 20, 2019 • Indonesia Geoid Model • Philippine Geoid Model Geoid Models
- 41. 1. Location Based Services 2. Civil Applications 3. Surveying, Mapping and GIS 4. GNSS-based Products 5. Space Applications 6. Scientific Applications 7. Military Applications 8. Autonomous Applications 9. Other Applications GNSS Applications
- 42. • Location based Information Streams - consists on pushing information to the user depending on its location and on the assumption that this information will be useful and welcomed by the user (e.g. alerts or warnings, nearest services, location-based advertising) • Tourist Information - provide guidance and landmark information to tourists typically in urban environments • Games – mostly in GNSS enabled mobile devices such as geocaching, scavenger hunts, role playing and adventure games (e.g. catching Pokemon) • Carpooling and Transport on Demand - arranged rides that vary from informal pick-points, manned booking agencies to web based booking sites[ 1. Location Based Services
- 43. • Personal Applications – pedestrian navigation, outdoor navigation, social networking, photography geocoding, location-based services • Road Applications - road navigation, tolling, emergency services, traffic management, fleet management & vehicle tracking • Aviation Applications - GNSS Augmentation (ABAS, GBAS and SBAS), en route navigation, approach, attitude determination, air traffic control • Rail Applications - train control and signaling, passenger traffic or transportation of dangerous goods, fleet management, goods tracking and other logistic information management • Maritime Applications - observing the changes of sea level, dredging operations, wrecks location, laying pipe lines, search and rescue of sinking vessels, dynamic positioning, positioning of oil rigs and fixing of satellite sea launch platforms, Automatic Identification System (AIS), Vessel Traffic Service (VTS) • Industry Applications - precision agriculture, package and container tracking, mining 2. Civil Applications
- 44. • Land Surveying – GNSS provides very high accuracy positioning for geodetic and projects control establishment • Mapping & GIS - data capture, digital map displays, low-cost mapping of infrastructures • Aerial Survey - manned and unmanned aeroplanes where the sensors (cameras, radars, lasers, detectors, etc) and the GNSS receiver are setup and are calibrated for the adequate georeferencing of the collected data. 3. Surveying, Mapping and GIS
- 45. • Personal Products - handheld outdoor receivers, sport watches & computers, phones, personal trackers • Road Products - Personal Navigation Devices (PND) and vehicle trackers • Aviation Products - flight management system (FMS), flight decks and avionics, or glass cockpit equipped with GNSS receiver • Maritime Products – chartplotters that include navigation in 3D maps, integration of other sensors and devices, such as barometric altimeter, depth sounder, electromagnetic compass or radar and fishfinder location capabilities 4. GNSS-based Products
- 46. • Precise Orbit Determination – precise orbit means precise positioning. Precise orbits are calculated in post processing (usually on the ground segment) based on the analysis of the actual orbits of the satellite • Satellite Realtime Navigation - navigation of spacecraft, Automated Transfer Vehicle (ATV) (expendable, unmanned resupply spacecraft) • Satellite Formation Flying - relative positions of the satellites must be maintained precisely as they close in 5. Space Applications
- 47. • Earth Sciences - geodesy and geodynamics, remote sensing using GNSS-Reflectometry (GNSS-R); physics of the ionosphere and troposphere. • Space-time Metrology - comparison of distant clocks, assessment of the properties of (primary) frequency standards • Fundamental Physics - relativistic mechanics (synchronisation of distant clocks, relativistic effects); quantum mechanics (quantum communication, relativity and earth gravitational field) 6. Scientific Applications
- 48. • Military Navigation - forces location, forces navigation, forces deployment, all weather and around the clock operations, communication network timing, remotely operated vehicles, signal jamming/anti-jamming • Target Acquisition - target acquisition systems, missile precision guidance 7. Military Applications
- 49. • Autonomous Driving - GNSS receptor and antenna providing position to the car's autopilot system • Autonomous Flying - Advanced UAVs (Unmanned Aerial Vehicles) are used in missions covering security, surveillance of infrastructures, search and rescue, mapping, fisheries, agriculture, forestry, natural resource monitoring, fire fighting and emergency management, airborne communication collection and relay, weather data collection, environmental monitoring, pollution detection and other scientific research 8. Autonomous Applications
- 50. • Precise Time Reference • network synchronization for power generation and distribution, • communication networks - real-time video, video conferencing, bank-to-bank encrypted exchange • data encryption and security - electronic encryption, signature and time- stamping rely on highly precise time references especially in the financial sector On GPS time: “Cell towers use it to route your phone calls, ATMs and cash registers use it for your transactions, electrical grids use it to send power to your house, and stock exchanges use it to regulate the trades that go into your stock portfolio or investment fund”-Tim Fernholz • Atmospheric Sensing – delay in the GNSS signal can be used for sensing the upper atmosphere e.g GNSS occultation 9. Other Applications
- 51. End of GNSS Lecture 1