SN207 GNSS Fundamentals Lecture PDF

SN207 Fundamentals of GNSS 01: Overview of current Global Navigation Satellite Systems (GNSSs) Dr Mohamed Elfarran Assistant Professor of Aerospace Engineering SN207 – GNSS Fundamentals Dr M...

SN207 Fundamentals of GNSS 01: Overview of current Global Navigation Satellite Systems (GNSSs) Dr Mohamed Elfarran Assistant Professor of Aerospace Engineering SN207 – GNSS Fundamentals Dr Mohamed Elfarran 1 [10/8/2022 10:33 PM]  Outline Terms: GNSS & GPS? Why do we use GNSS? What is GNSS? How does GNSS Work? What do you need to know about GNSS? What can you do with GNSS? How is GNSS used in the real world? SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  GNSS and GPS GPS = Global positioning system – GPS refers to the constellation of navigation satellites associated with the American System (which is a global system). – For a long time, GPS was the ‘only game in town’, so everything (satellites, receivers, etc.) was referred to as “GPS” – Times are changing… other options (besides GPS) are quickly developing SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM] GNSS = Global Navigation Satellite System GNSS is an umbrella term that includes any satellite navigation system. Options include: – GPS (U.S. | operational since 1994) – GLONASS (Russian | ‘re-operational’ since 2010) – Galileo (European Union | anticipated operation:2019) – Compass (China | Operational in Asia/Pacific since 2012 / anticipated global operation: 2020) SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  Why GNSS? Many features have addresses and landmarks that are associated with a destination. Fred Jones 332 Elm St. Frog Holler, VA 42534 SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  Why GNSS? However, there are many features that do not have addresses… There are many MAJOR cities that do not even have STREET NAMES! And then there is the open ocean and sky… SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  Why GNSS? Location, Location, Location and INFORMATION!!! SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  Pre-GPS Navigation is critical Historical Navigational tools have limits: – The Sextant – doesn’t work if it is cloudy – Lowrance – radionavigation: only worked near land… The military had its own reasons for determining location… – Identify targets – Friendly fire issues – “smart bombs” SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  What is GNSS… And how does it work? SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  What is GPS? GPS (and GNSS) is not a single UNIT! GPS = Global Positioning SYSTEM GPS was developed by the Department of Defense at a cost of >$12 billion Funding for the GPS was contingent on making the system available to the public. SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  GPS (and GNSS) is a SYSTEM There are three major components in this system: 1. Satellites 2. Ground Control Stations 3. GNSS Receivers (or units) SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  Satellites There are 24-32 satellites up there at any given time orbiting the earth at ~11,000 naut. miles. ▪ The DOD knows the EXACT location of each of the satellites at any given moment. ▪ These satellites have VERY accurate clocks on board. ▪ The satellites continuously send radio signals towards earth. ▪ These radio signals are picked up by GPS receivers. Dr Mohamed Elfarran SN207 – GNSS Fundamentals [10/8/2022 10:33 PM]  Satellites: “A Beehive of Activity” SN207 – GNSS Fundamentals http://www.nasa.gov/multimedia/imagegallery/image_feature_1283.html Dr Mohamed Elfarran [10/8/2022 10:33 PM]  GPS Control Stations ◼ There are five control stations that monitor the satellites. Control stations enable information on Earth to be transmitted to the satellites (updates and fine turning). Control stations continuously track satellites, and update the positions of each satellite. Without control stations, the accuracy of the system would degrade in a matter of days. SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  GPS Receivers GPS units are referred to as “receivers”. They receive information (radio signals) from satellites. The GPS receiver knows how long it takes the signal to travel from the satellite to the receiver. SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  GPS Receivers The GPS receiver knows how long it takes the signal to travel from the satellite to the receiver. The Receiver is therefore able to calculate its distance from the satellite. Distance = time x velocity Distance = time x 186,355 mi./sec. The receiver can calculate the time that signal traveled from the satellite to the receiver. The receiver is therefore able to determine its exact distance from the satellite. SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS (and GNSS) Works One satellite… SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS Works If the GPS receiver only obtains signals from 1 Satellite, then it “knows” that it is located somewhere on this sphere… SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS Works SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS Works If the GPS receiver only obtains signals from 2 satellites, then it “knows” that it is located somewhere where these 2 spheres intersect SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS Works SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS Works If the GPS receiver obtains signals from 3 satellites, then it “knows” that it is located somewhere where these 3 spheres intersect (2 points) SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS Works SN207 – GNSS Fundamentals Dr Mohamed Elfarran [10/8/2022 10:33 PM]  How GPS Works A fourth satellite is required to determine the SN207exact location and – GNSS Fundamentals Dr Mohamed Elfarran elevation. 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