UNIT 4 MODULE 1 Global Positioning System GPS

UNIT 4 – MODULE 1: Global Positioning System (GPS)

INTRO TO GPS • Provides users with navigation, position and time, in all weather conditions, anywhere on Earth. • Achieved through a constellation of satellites in Medium Earth Orbit (MEO). • The entire GPS is called the NAVigation Statellite Timing And Radar (NAVSTAR).

HISTORY OF GPS * • 1974 – First of many GPS satellites launched into space. • 1983 – President Ronald Reagan orders the GPS to be made public for civilian use. • 1994 – Constellation of 24 satellites completed. • 2000 – Full GPS signal quality becomes available for civilian use. • 2005 – First of several second-generation satellites launched. • 2017 (Est. ) – First of several third-generation satellites to be launched.

GPS MANAGEMENT • The entire system is managed by the U. S. Air Force. • Master control station located at Shriever Air Force Base in Colorado. • Performs atmospheric corrections to the military GPS service for improved accuracy. Credit: U. S. Air Force

CONTROL SEGMENT • Master Control Station (MCS) • Ground Antennas • Monitor Stations – Air Force – Alternate MCS – Remote Tracking – National Geospatial. Intelligence Agency (NGA) Credit: www. gps. gov

GPS SATELLITES • At least 24 required to maintain global coverage. • 32 currently in orbit to ensure any losses are immediately covered. • Four or more operate in six different orbital planes (MEO). Credit: Wikipedia/El pak Credit: Penn State

GPS SATELLITES (Continued) • Revolve around Earth ~ every 12 hours (twice a day). • Have an altitude of 20, 200 km (12, 550 miles). • Always sending out radio signals. • We know where they are at all times.

HOW GPS WORKS • Measures the time it takes a radio signal (from a satellite) to reach a ground receiver. • Radio signal travels at the speed of light (300, 000 km/s). It’s a fixed speed. • The GPS receiver on the ground notes the signal’s exact arrival time, and uses to calculate its distance from each satellite signal. Credit: Gawler Wheelers

HOW GPS WORKS (Continued) • Once the receiver knows its distance from each satellite, it can determine location. • The information contained within a GPS signal includes: – Precise Time – Location – Status Credit: University of Colorado - Boulder

TRILATERATION • Positioning from three distances. • GPS receivers use trilateration for determining position via signal calculations from three satellites. • Three satellites identify position and a fourth is used for increased accuracy. Credit: BBC *

ATOMIC CLOCKS • Synchronize time for our technology. • Most precise time keeper that’s built into every GPS satellite. • Accurate to within 100 billionth of a second. • Precise time needed for communications, power grids, finance networks, etc. Credit: University of Alaska - Fairbanks

* GPS ERROR • Can result from a number of sources: – Tall Buildings – Atmospheric Effects – GPS Receiver Clock Credit: Berkeley Lab • Signal acquisition also limited when underground or underwater. Credit: NASA

GPS RECEIVERS • Different types of GPS receivers (e. g. handheld, vehicle). • Most handheld are waterproof, have a battery life of 15+ hours, and are equipped with a barometer, compass and altimeter. • Smartphones can act as GPS receivers, but have many limitations. Credit: www. trimble. com Credit: Wessex Archaeology

GPS RECEIVERS (Continued) • GPS receivers for the car have several capabilities: – Various Map Displays – Step-by-Step Directions – Real-Time Traffic Updates & Alternate Route Suggestions – Identify Nearby Amenities (e. g. Gas Station, Tourist Attractions, Restaurants) Credit: blog. autointhebox. com Credit: http: //www. imgneed. com

GPS SIGNALS • Four signals available for civilian use: – L 1 C/A – L 1 C – L 2 C – L 5 • Restricted signals for military use: – P Code – M Code Credit: Mina Shin

APPLICATIONS: AGRICULTURE • Farm Planning • Field Mapping – Boundaries – Irrigation Systems – Problem Areas (e. g. weeds, disease) • Soil Sampling • Tractor Guidance • Crop Scouting Credit: UC Davis *

APPLICATIONS: AVIATION • Real-Time, Accurate Positioning Information • Enhanced Route Selection • Increased Safety (Air & Ground) • Reduced Delays Credit: http: //www. stephan-schwab. com *

APPLICATIONS: EARTHQUAKES • When used with sensors, GPS can be used to evaluate & predict earthquakes. • Allows for the precise measurement of elevation changes, land tilt and horizontal movement along fault lines. Credit: Scripps Institution of Oceanography *

APPLICATIONS: ENVIRONMENT • • Pattern Identification Disaster Tracking Wildlife Preservation Enhanced/In-Depth Analyses for Assessing Environmental Issues • Resource Management Credit: www. gps. gov Credit: NOAA

APPLICATIONS: OUTDOOR ACTIVITIES • Provides highly-accurate weather positioning information. • Reduces chances of getting lost in remote areas. • Many activities can involve GPS: Credit: www. garmin. com – Skiers – Runners & Cyclists – Hiking & Mountain Climbing Credit: www. pacsafe. com

APPLICATIONS: ROADS & HIGHWAYS • Increased Safety & Mobility • Improved Monitoring of Traffic Conditions • Reduced Road Surveying Costs • Enhanced Logistics Credit: Wei Fang/Getty Images

APPLICATIONS: SURVEYING & MAPPING • More Accurate/Reliable Data Acquisition • Reduced Operational Limitations • Enhanced Productivity: – Time – Labor – Equipment Credit: Leica Geosystems

APPLICATIONS: TIME • Global Access to Atomic Clock Time • Synchronization is necessary for highly critical infrastructure: – Communications – Power Grids – Financial Systems Credit: Casio