1. GPS Basics A very brief overview! by Monica Spicker 2007 Some figures are copyrighted and used with the kind permission of Dr. Peter H. Dana. B M O C
2. Several Systems B M O C US: NAVSTAR - NAV igation S ystem with T iming A nd R anging, DOD Russia: GLONASS GLO bal N avigation S atellite S ystem. No yet complete European Union: Galileo (complimentary to US GPS) – started in 2003. Recently joined by various middle and far eastern countries. Japan: local regional system - Quasi-Zenith Satellite System (QZSS) with 3 satellites China: Twinstar Rapid Positioning System or Beidou Navigation System – pairs geosynchronous satellites, compatible with Galileo
5. Control System B M O C Image copied from http://www.aero.org/publications/crosslink/summer2002/04.html
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11. Determining position : 3 satellites for position. 4 needed for elevation B M O C 1 satellite: Solution is a hollow sphere 3 satellites: 2 points on a line. One pt is “in space”and thrown out 2 satellites: Solution is a circle. distance GPS satellite
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13. Sources of error: Amt of error B M O C Satellite Geometry 4 – 6m* Multi-path errors Variable Ionosphere (charged particles) < 2m Troposphere (the dense part) < 2m Receiver errors (timing, clock, antenna) < 2m Satellite clock errors < 1m Ephemeris errors (satellite position) < 1m * Planning programs are available to predict times with best geometry. Afternoons in northern hemisphere generally have poorest geometry. Orbits have widest gaps in the north.
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15. GPS cannot “see” through objects! B M O C Some of the newer satellites and receivers can receive through thinner solid objects like cars, buildings and anything wet like tree canopies, people, heavy rain, etc. Terrain is still too big through which to get a signal!
16. Multipath error B M O C Increases the length of time for a signal to reach the receiver.
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18. B M O C TEST 1. Why is this equatorial rainforest wildlife biologist sitting on a horse in the middle of a river? 2. What problems is she likely to be having (with her GPS unit)?
25. B M O C Beacons operated by the U.S. Coast Guard & U.S. Army Corps of Engineers. Many inland states have own beacons. In most of the world, inland areas do not have access to this type of data.
