Introduction To Global Positioning System and other Geo-technologies Lecturer – Jun Liang Office – 218 Saunders

Lecture 1 – Basic Concepts Location Problem Examples – Point: Where am I? Tree location; 911 calling stations; Point: Where am I? Tree location; 911 calling stations; Line: Bike trails; New streets; animal activities; Line: Bike trails; New streets; animal activities; Polygon: land parcels; buildings; water body; Polygon: land parcels; buildings; water body; Methods – Traditional Survey; New technologies – Navigation Star. Traditional Survey; New technologies – Navigation Star.

NAVSTAR NAVigation System with Time And Ranging (Navigation Star”) – A constellation of from 24 to 32 satellites orbiting the Earth, broadcasting data that allows users on or near the Earth to determine their spatial positions. GPS in USA. Russians – GLONASS.

Coordinates and References 2D – latitude and longitude (actually it is 3D, since diameter of Earth is not a constant value.) Absolute VS relative coordinates References – Sun, Earth, Chapel Hill, Durham, Saunders Hall, Old Well, Control points, etc. References – Sun, Earth, Chapel Hill, Durham, Saunders Hall, Old Well, Control points, etc. Recording: 38N, 84.5W; 100 Meters east of Saunders Hall; 50 Miles West of Raleigh Recording: 38N, 84.5W; 100 Meters east of Saunders Hall; 50 Miles West of Raleigh

Positions from GPS Absolute Positions – could be reset in GPS receivers. Latitude, Longitude => UTM Latitude, Longitude => SPC Advantages of using GPS: High positioning accuracy, from meters down to the millimeter level High positioning accuracy, from meters down to the millimeter level Availability Availability Capability of determining velocity and time, to an accuracy commensurate with position. Capability of determining velocity and time, to an accuracy commensurate with position. Time/Velocity Time/Velocity No inter-station visibility No inter-station visibility

Anatomy of the term: “Global Positioning System” Global: anywhere on Earth, but not: Inside buildings Inside buildings Underground Underground In very heavy tree canopy In very heavy tree canopy Around strong radio transmissions Around strong radio transmissions In “urban canyons” amongst tall buildings In “urban canyons” amongst tall buildings Near powerful radio transmitter antennas Near powerful radio transmitter antennas Or anywhere else not having a direct view of a substantial portion of the sky.

Anatomy of the term: “Global Positioning System” (Cont.) Positioning – Where are you? Where are you? How fast are you moving and in what direction? How fast are you moving and in what direction? In what direction should you go to get to some other specific location In what direction should you go to get to some other specific location How long would it take at your speed to get there? How long would it take at your speed to get there? Where have you been? Where have you been?

Anatomy of the term: “Global Positioning System” (Cont.) System: A collection of components with connections (links) among them: The Earth The Earth Earth-Circling Satellites Earth-Circling Satellites Ground-Based Stations Ground-Based Stations Receivers Receivers Receiver Manufacturers Receiver Manufacturers The United States Department of Defense The United States Department of Defense Users Users

The Earth The mass of the Earth holds the satellites in orbit – each satellites is trying to fly by the Earth at 4KM per second. The surface of the Earth is studded with little “monuments” – whose coordinates are known quite accurately, allow us to determine the position of any objects we choose on the surface of the Earth.

Earth-Circling Satellites solar-powered radio transmitters Forms a constellations such that several are “visible” from any point on Earth at any given time First one Feb 22, 1978; Mid-1994 all 24. 3/24 are spares Block IIR – middle altitude (20,400 Km), below geostationary satellites (35,763 Km).

Earth-Circling Satellites (Cont.) NAVSTAR satellites -Neither polar nor equatorial, but slice the Earth’s latitudes at about 55 degree. -Executing a single revolution every 12 hours. -There are 6 distinct orbital planes (A, B, C, D, E, F) -There 4 or 5 satellites in each planes.

Earth-Circling Satellites (Cont.) A satellite has three key pieces of hardware: Computer Atomic Clock Radio transmitter All GPS Satellites carry NUDET sensors.

Earth-Circling Satellites (Cont.) Speed km/sec Weight – 1077 Kg Length – 11.6 meter Solar panel – 1100 watts (The radio on board uses 40 watts); also has backup battery installed (solar eclipse) Two Radio channels – L1( Mhz) and L2 ( MHz) Each has 4 atomic clocks. (a billionth of a second) Each is worth $65 million and can last 10 years.

Ground Based Stations GPS Satellites’ tracks are influenced by (1)gravitational effects of the moon and sun (2)Solar wind (3)System error Thus both their tracks and innards requires monitoring. GPS ground stations are used to control GPS movements and maintain accurate system setting (such as removing clock errors.)

Ground Based Stations (Cont.) There are five ground facility stations: Hawaii, Colorado Springs, Ascension Island, Diego Garcia and Kwajalein. All stations are operated by the US Department of Defense All five stations are Monitor Stations, equipped with GPS receivers to track the satellites. The resultant tracking data is sent to the Master Control Station (MCS).

Ground Based Stations (Cont.) Each satellite passes over at least one monitoring station twice a day. Information developed by the monitoring station Rebroadcasts to receivers Health of the SAT Real tracks VS expected tracks Current almanac for all SAT Other subjects

Ground Based Stations (Cont.) Almanac – a description of the predicated positions of heavenly bodies. Ephemeris - contains orbital information that allows the receiver to calculate the position of the satellite. Clock information – Coarse Acquisition (C/A) code and Precise (P) Code.

Ground Based Stations (Cont.) Colorado Springs is the MCS, where the tracking data processed in order to compute the satellite ephemerides (or coordinates) and satellite clock error parameters. It is also the station that initiates all operations of the space segment, such as spacecraft maneuvering, signal encryption, satellite clock-keeping, etc. Three of the stations (Ascension Is., Diego Carcia, and Kwajalein) are Upload Stations through which data is telemetered to the satellites.

Receivers GPS receivers consists of An antenna An antenna Electronics Electronics A microcomputer A microcomputer Controls (buttons, keys) Controls (buttons, keys) A screen A screen Computer memory Computer memory Radio Radio Etc. Etc.

Receivers (Cont.) GPS units receive two types of data from NAVSTAR satellites: AlmanacEphemerisChannels Originally 4-5 Now most

Receivers (Cont.) Garmin Left – ETREX 12 Channels Right - GPSMAP60 12 Channels Trimble XT, XH handhelds – 12 Channels MS860™ receiver is a 36-channel L1/L2 RTK GPS receiver

Receivers (Cont.) Differential Corrections Using the RTCM (Radio Technical Commission for Maritime Services) SC- 104 format input Using the RTCM (Radio Technical Commission for Maritime Services) SC- 104 format input Low cost WAAS (Wide Area Augmentation System) receiver From GPS to PC or other devices - using the NMEA0183 protocol

Receivers (Cont.) Other protocols – SiRF SiRF is a brand of microcontroller designed to be used with GPS systems. SiRFstar III – used by Garmin, Tomtom and Magellan and other GPS manufactures. Faster fix time Faster fix time Higher signal locking and tracking sensitivity lower power requirements

Receivers (Cont.) Receiver types Consumer models Consumer models U.S. military/government models U.S. military/government models Mapping/resource models Mapping/resource models Survey models Commercial transportation models

Receivers (Cont.) Consumer models Big three – Garmin ( Magellan ( and Lowrance ( Big three – Garmin ( Magellan ( and Lowrance ( Most are 12-channel parallel receivers Prices are reasonably low – less than $100 Location precision is low (15 meter most)

Receivers (Cont.) U.S. military/government models Can receive P-code and Y-code (only to the government.) Called PLGR (Precision Lightweight GPS Receivers) - Accuracy – within 4 meters Light Weight and no need to post processing

Receivers (Cont.) Mapping/resource models Data can be input into a GIS application More precise than consumer models – from submeter to several meters More expensive – A Trimble XH handheld costs about $5000, and A XT costs about $4000.

Receivers (Cont.) Survey models Purpose – surveying land, access points, sampling of small objects Extremely precise – down to centimeter/millimeter Tends to be large and complex to use Very expensive Where did I put it?

Receivers (Cont.) Commercial transportation models These GPS receivers are usually installed in moving objects (aircraft, ships, cars, trucks, etc.) Provide navigation supports (where am I type questions; optimizing routes; finding service facilities etc.) Can send location info to a monitoring facility through APRS.

Manufacturers, DOD and Users Manufacturers - Note: some just manufacture GPS “engine”, the other may provide a computer unit. Note: some just manufacture GPS “engine”, the other may provide a computer unit. DOD manages GPS satellites and ground control units. (SA was turned off by DOD on May 2000) Users – more people than ever are using GPS, it will become as popular as MP3.

Other positioning systems Galileo EU and USA agreed on March 2002 to introduce their own alternative to GPS, called Galileo. The first satellite was actually launched on 28 December The receivers will be able to combine the signals from 30 Galileo and 28 GPS satellites to greatly increase the accuracy. The System will be working from 2010.

Other positioning systems GLONASS It is operated for the Russian government. The first test SATs were launched in were launched by 1991 The constellation was not completed until December 1995 Only eight SATs in operation in April 2002