Hay_Topic 14_GNSS_use (1).pdf

Geog 380: Geospatial Communication Source: https://earth.nullschool.net Topic 14: GNSS GEOG 380 - Topic 14 © Geoffrey Hay (2023) 1 Learning outcomes By the end of this lecture topic, a successful student will be able to: § § § § § Recall the different GNSS that are integrated into many device...

Geog 380: Geospatial Communication Source: https://earth.nullschool.net Topic 14: GNSS GEOG 380 - Topic 14 © Geoffrey Hay (2023) 1 Learning outcomes By the end of this lecture topic, a successful student will be able to: § § § § § Recall the different GNSS that are integrated into many devices Explain the basis for GNSS positioning Explain basis for Differential GNSS Recognize GBAS and SBAS Recognize some of the technologies for indoor positioning GEOG 380 - Topic 14 2 https://geekflare.com/gnss-vs-gps-technology/ § How GNSS Works: https://www.youtube.com/watch?v=CCKisghkcA4 (2:44 mins) § How GPS works: https://www.youtube.com/watch?v=ldusExdni0A (4.06 mins) § How RTK works: https://www.youtube.com/watch?v=ieearzWTCZw (5:16 mins) GEOG 380 - Topic 14 3 How It Works: Ranging (distance) § Satellites broadcast a time code § GNSS receivers calculate range (distance) to satellites using travel time of signal (radio waves at speed of light 3.0x10^8m/s) § Calculating successive ranges for two or three additional satellites allows for the use trilateration to fix position in 3D space. § Usually need 4 satellites § Technically only need 3 satellites, the fourth one is a check § More satellites usually means better location GEOG 380 - Topic 14 4 Satellite “Triangulation” § Measured distance to multiple (min 3-4) satellites in space to determine locations on earth § NOT triangulation, since there are no angles involved https://core-electronics.com.au/tutorials/how-GPS-works.html GEOG 380 - Topic 14 5 Trilateration not Triangulation § § Trilateration: a GPS receiver measures the distance (not angles) to satellites using radio signals. Triangulation: The positions of the points of interest are computed based on measured angles and two know points. From those angles, the distances are computed which are in turn used to calculate coordinates for the target points. https://gis.stackexchange.com/questions/17344/differences-betweentriangulation-and-trilateration GEOG 380 - Topic 14 6 Measuring Distance From a Satellite § Velocity (m/s) x Time (s) = Distance (m) § Velocity is known (estimated) § Time = offset of receiver clock and signal sent from satellite clock http://www.azosensors.com/Article.aspx?ArticleID=29 GEOG 380 - Topic 14 § Navigation message includes information on orbital parameters, clock corrections and other system updates 7 Measuring Time at “Light Speed” § An error of 1/1000 of a second would translate into a 500 km mistake § Speed of light (EMR) in a vacuum ~ 3x108m/s or 300,000 km/sec § Satellites carry atomic clocks, but what about receivers? à Receivers carry quartz crystal clocks = less accurate àThus, the all-important extra (4th) satellite measurement § The fourth satellite measure is a cross-check. Errors uncover inaccuracies in the receiver clock, which are then corrected by the CPU on the device GEOG 380 - Topic 14 8 Errors: Noise, Bias, & Blunders § Noise § Code noise § Bias § Selective availability à an intentional degradation of public GPS signals implemented for national security reasons à Discontinued May 2000 § Atmospheric effects § Multipath interference § Human blunders http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html GEOG 380 - Topic 14 9 GPS Accuracy § With Selective Availability (pre-2001) § 45m horizontal 100m vertical GEOG 380 - Topic 14 § Without Selective Availability (post 2001) § 7m horizontal 35m vertical 10 Geometric Dilution of Precision (GDOP) § Widely-separated satellites can minimize error http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html GEOG 380 - Topic 14 11 Visibility and GDOP http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html GEOG 380 - Topic 14 12 Differential GNSS § Accuracies in the order of centimetres § Key is a second, reference receiver that remains stationary à Because satellites are so high (20,000 km) you can assume that accuracy and timing errors affect both receivers the same § Goal is to filter out atmospheric effects § Real-time Kinematic (RTK) https://en.wikipedia.org/wiki/Realtime_kinematic_positioning#/media/File:Real_time_kinematic.svg GEOG 380 - Topic 14 § Analysis of the signals (phase) 13 Differential GNSS Operation § Towers transmit errors to roving receivers via radio waves § Enabled receivers can collect this information and make corrections in real-time § Basis for Ground-based Augmentation Systems (GBAS) http://www.colorado.edu/geography/gcraft/notes/gps/gif/difnav.gif GEOG 380 - Topic 14 14 SBAS - Satellite Based Augmentation Systems § Regional SBAS improves the accuracy and reliability of GNSS information by correcting signal measurement errors. It uses GNSS measurements taken by accurately located reference stations deployed across an entire continent § USA: Wide Area Augmentation System (WAAS) § Japan: Michibiki Satellite Augmentation System (MSAS) § India: GPS-aided GEO-Augmented Navigation (GAGAN) § China: BeiDou SBAS (BDSBAS) (in development) § South Korea: Korea Augmentation Satellite System (KASS) (in development) § Russia: System for Differential Corrections and Monitoring (SDCM) (in development) § ASECNA: Augmented NaviGation for Africa (ANGA) (in development) § Australia and New Zealand: Southern Positioning Augmentation Network (SouthPAN) (in development) https://www.youtube.com/watch?v=QK9tzzskG5Y (4:19 mins) https://www.euspa.europa.eu/european-space/eu-space-programme/what-sbas GEOG 380 - Topic 14 15 SBAS - Satellite Based Augmentation Systems § § § All of these systems comply with a common global standard and are therefore: Compatible: they do not interfere with each other; Interoperable: a user with a standard receiver can benefit from the same level of service and performance, regardless of what coverage area they are located in. https://www.euspa.europa.eu/european-space/eu-space-programme/what-sbas GEOG 380 - Topic 14 16 Satellite Based Augmentation Systems (SBAS) e.g., WAAS and EGNOS § WAAS § Wide area augmentation system – available in America § Providing horizontal and vertical navigation information for civil aviation § EGNOS § European Geostationary Navigation Overlay Service § Consists of 3 geostationary satellites over Europe + ground stations. § Improves performance of GNSS – ie., ionosphere delays affecting the user. https://www.flightglobal.com/satellite-navigation-what-is-waas/egnos/69463.article GEOG 380 - Topic 14 § Forms of differential GNSS 17 WAAS - Wide area augmentation system § Network of permanent base stations § WAAS - USA/southern Canada § EGNOS – Europe http://www8.garmin.com/aboutGPS/waas.html GEOG 380 - Topic 14 § Plus, geosynchronous satellites to broadcast correction code § GPS accuracies 1-3 metres for common handheld GPS units with extra receiver built-in or separate WASS: https://www.youtube.com/watch?v=_MhfaQma5SA&t=1s 18 How does your phone calculate location § GNSS § Cell towers § Indoor positioning system (IPS) – becoming big business § § § § § § § WiFi Beacons Inertial Near-field communication (NFC) Bluetooth RFID (radio frequency identification) Magnetic https://famisafe.wondershare.com/ GEOG 380 - Topic 14 19 https://www.geospatialworld.net/blogs/top-5-gnss-trends-2018/ § European GNSS in a nutshell: https://www.youtube.com/watch?v=gffG5sTegT4&t=192s (3:12 mins) GEOG 380 - Topic 14 20