Satellite Based Positioning.
- 2. Application fields Surveying Military operations Engineering Vehicle tracking Flight navigation Car navigation Ship navigation Agriculture Mapping
- 3. Topics for discussion The segments of a satellite-based positioning system GPS, GLONASS and Galileo Principle of positioning Errors and their sources Positional accuracies Relative (differential) positioning
- 4. Three segments Space segment: the satellites that orbit the Earth, and the radio signals that they emit. Control segment: the ground stations that monitor and maintain the space segment components. User segment: the users with their hard- and software to conduct positioning.
- 5. Space segment of GPS system The space segment of GPS consists of 24 satellites on 6 orbits (approx. 22,000 km from the centre of the Earth): Each satellite carries a clock. Each satellite completes 2 orbits/day. 24 hour complete GPS coverage anywhere on the Earth. Accuracy: 21 meters 95% of time NAVSTAR GPS Satellite
- 6. L2 Carrier L1 Carrier P-Code P-Code C/A Code Navigation Message Navigation Message 1227.60 MHz 1575.42 MHz GPS Signal Structure
- 7. Control Segment of GPS Space Segment 24+ Satellites Current ephemeris is transmitted to users Monitor Stations • Diego Garcia • Ascension Island • Kwajalein • Hawaii • Colorado Springs GPS Control Colorado Springs End User
- 8. Control Segment of GPS Master Control Station Monitor Station Ground Antenna Colorado Springs Hawaii Ascension Islands Diego Garcia Kwajalein
- 9. User segment of GPS Receivers and their users: (Military) Navigation in 3D-aircrafts, ships, ground vehicles and hand-carried instruments Precise positioning - Surveying (Time dissemination - astronomy) (Research projects on atmospheric distortions) GPS-Receivers
- 10. Selection of a GPS receiver Application (boating, flying, driving, mapping, surveying) Accuracy requirements Power consumption requirements Operational environment Signal processing requirements Cost Data exchange standards
- 11. Space segment of GLONASS system Russian system (Globalnaya Navigatsionnaya Spunikova Sistema - GLONASS) 24 satellites (21 operational and 3 spare). Three orbital planes at 65º inclination. Two codes as GPS, but all satellites broadcast identical codes but using slightly different carrier frequencies for each satellite. The positioning principal is the same as GPS Accuracy: 20 m horizontal and ~30 m vertical GLONASS Satellite http://www.glonass-ianc.rsa.ru
- 12. Space segment of Galileo system Galileo is in the implementation phase, first satellite to be launched in 2006, planned operation start 2008. Designed for civil purposes 30 satellites 3 orbits (23,222 km high) Network of ground stations, 2 control centresin Europe Accuracy of single receiver: around 1 m http://www.esa.int/esaNA/SEMY02FFWOE_galileo_0.html Galileo Satellite
- 13. Principle of positioning GPS-receiver GPS-satellite Distance = (velocity of light) x (travel time) The GPS-receiver computes the distances (ranges) to the satellites The GPS-receiver computes the distances (ranges) to the satellites How does the GPS-receiver computes the travel time? How does the GPS-receiver computes the travel time?
- 14. L2 = 1227.60 MHz L1 = 1575.42 MHz GPS code on Carrier wave (C/A or P code) It receives GPS-codes and Carrier waves from the satellite It receives GPS-codes and Carrier waves from the satellite
- 15. Code from Satellite Code from Receiver Time difference between Receiver and Satellite signal ∆t Code comparison
- 16. Principle of positioning GPS-receiver GPS-satellite Pseudo-range = (velocity of light) x (travel time) + (receiver clock error) + (other errors) The GPS-receiver measures in fact pseudo distances (pseudo-ranges) to the satellites The GPS-receiver measures in fact pseudo distances (pseudo-ranges) to the satellites
- 17. Principle of positioning (X,Y,Z) 1 2 3 distance 1 distance 2 distance 3 To determine a position in a 3 dimensional space it takes in theory 3 distance measurements from 3 satellites To determine a position in a 3 dimensional space it takes in theory 3 distance measurements from 3 satellites
- 18. Pseudorange positioning Three-satellite fix position (trilateration) Two-satellite fix position One-satellite fix position
- 19. (X,Y,Z,∆ ∆ ∆ ∆t) 1 2 3 4 pseudorange 1 pseudo- range 2 pseudo- range 3 pseudorange 4 Pseudorange = velocity of light * travel time + receiver clock error + other errors Accurate positioning requires an extra distance measurement from a fourth satellite to eliminate the receiver clock error Accurate positioning requires an extra distance measurement from a fourth satellite to eliminate the receiver clock error Principle of positioning
- 20. Synchronization bias of the receiver clock
- 21. Error sources in absolute positioning Selective availability Satellite clock and orbit errors Ionospheric and tropospheric delays Receiver’s environment (multi-path) Satellite constellation
- 23. Magnitude of the error sources* * Absolute, single-point positioning based on code measurements *
- 24. Good satellite constellation Low PDOP (1.5) Good satellite constellation Low PDOP (1.5) Bad satellite constellation High PDOP(5.7) Bad satellite constellation High PDOP(5.7) Satellite constellation positional error
- 25. Positional accuracy in absolute positioning Absolute, single-point positioning based on code measurements: Typical error: 5-10 m (horizontal accuracy) Typical error: 2-5 m (horizontal accuracy) when using a dual- frequency receiver or the encrypted military signals (P-code)
- 26. Location errors: noise, bias and blunder Noise (random) errors: noise in code and noise in receiver, multi-path. Bias (systematic) errors: clock, satellite position, ionosphere, troposphere, GDOP effects. Blunder: incorrect geodetic datum, software failures, hardware problems etc. Systematic errors (bias) removal is essential to improve the positional accuracy!
- 27. (X,Y,Z) Reference point Reference (or base) receiver Target (or field) receiver Differential (or relative) positioning Relative positioning
- 28. Positional accuracy in relative positioning Relative, single-point positioning based on code measurements: Typical error: 0.5 - 5m (horizontal accuracy)
- 29. Positional accuracy in relative positioning Relative, single-point positioning based on carrier phase measurements: Typical error: 2mm – 2cm (horizontal accuracy)
- 30. Carrier phase measurements Carrier phase measurement is a technique to measure the range (distance) of a satellite by determine the number of cycles of the (sine-shaped) radio signal between sender and receiver. The number of cycles is determined in a long observation session from the change in carrier phase (Phase Shift Keying). This change happens because the satellite is orbiting itself. L1/L2 Carrier
- 31. Relative (differential) survey techniques using carrier phase measurements Static Stop and go kinematic Pseudo-kinematic Kinematic Rapid static On-the-fly (OTF)/real-time kinematic (RTK)
- 34. Network positioning Relative positioning using a network of reference stations NLR Globalcom http://www.lnrglobalcom.nl GlobalNET 2005
- 35. Network positioning GlobalNET 2005: Reference Station at ITC
- 37. (X,Y,Z) Reference point Ground station Field receiver (X,Y,Z) Reference point Ground station Geostationary satellite Satellite-based Augmentation Systems
- 38. (X,Y,Z) Reference point Ground station (X,Y,Z) Reference point Ground station Geostationary satellite Satellite-based Augmentation Systems
- 39. Operational systems WAAS (Wide-Area Augmentation System) for North America EGNOS (European Geostationary Navigation Overlay Service) for Europe MSAS (Multi-functional Satellite Augmentation System) for eastern Asia
- 42. Wide Area Augmentation System (WAAS)
- 43. Local Area Augmentation System (LAAS)
- 44. INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION The end !
- 45. INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION Mobile GIS applications Data collection with a mobile computer
- 46. INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION Location-Based Services (LBS) Location-Based Services on a Mobile computer or mobile phone.
- 47. INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION Location-Based Services - Applications 1. Location based information services (e.g. search for the nearest restaurant or the nearest banking cash machine) 2. Location based emergency service (e.g. pinpoint your location on dialing 9-1-1) 3. Location based billing service (e.g. preferential billing for calling by establishing personal zones such as a home zone or work zone). 4. Fleet applications (tracking a vehicle and/or operator).
- 48. INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION LBS application - Mobile phone tracking http://geotracing.com/tland