Global Positioning SystemsGPS
GPS NavigationGlobal Positioning Satellite NavigationGarmin GPS 72Topographic MapsAerial Photography
What is GPS?The Global Positioning System is a network of 24 satellites placed into orbit by the U.S. Department of Defense. The satellites circle the earth twice a day in a very precise orbit and transmit information to earth. The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites "visible" in the sky.
GPS HistoryDevelopment began during the space race of the 1950s and 1960s
On October 4, 1957, the Soviet Union launched Sputnik I. The world's first artificial satellite, it was about the size of a basketball, weighing only 183 pounds. It took about 98 minutes to orbit the Earth on its elliptical path.Official Name: Iskustvennyi Sputnik Zemli (fellow world traveler of the earth)
Laika, the first living creature in space, traveled on Sputnik IISputnik II was launched on November 3, 1957, allowing them to continue their work.
GPS HistoryThe ability to determine a satellites orbit from the ground by using radio signals was the first step in developing an accurate space-based positioning system.Navy used this information to develop the worlds first satellite navigation system: Navy Navigation Satellite System (TRANSIT)..Final constellation consisted of three operating and three spare satellites in a 600-nautical-mile polar orbit, three ground control stations, and receivers on naval vesselsTerminated service on December 31, 1996 (replaced by GPS).
GPS HistoryIn the mid-1960's, the Air Force also initiated a program consisting of several satellites which would accurately determine the position of a vehicle moving on land or in the air. In 1973, the Navy and the Air Force programs combined to form a system called the Navigation System with Timing and Ranging (NAVSTAR) which became known as the Global Positioning System (GPS).
GPS HistoryGPS satellites continued to be launched to complete the GPS constellation.GPS satellites were payloads of the NASA Space Shuttle flights of the early 1980s.Launches suspended because of the Challenger accident in 1986.
GPS HistoryConstellation development continued into the 1990s.In 1991 GPS was first used in combat during Operation Desert Storm.Public awareness of GPS increases during the war.System reached full operational capability on July 17, 1995.Increasing use within the private sector.
GPS HistoryApproximately 1.4 million civilian GPS receivers have been produced each year since 1997GPS created an economic impact of $6.2 billion in 2000. Future expectations project that the economic impact of GPS technology may surpass $50 billion by the end of this year.
How GPS WorksThe GPS system actually includes three separate segments:SpaceControl User
Space SegmentGPS satellites are not in geo-synchronous (stationary) orbit, but instead circle the Earth at altitudes of 10,900 nautical miles (approx. 12,500 statute miles)Each satellite is on one of six orbital planes, inclined with respect to the equatorial plane by 55 degrees Configuration ensures that at least four satellites will be above the horizon anywhere on Earth simultaneously
Control SegmentIncludes three componentsMaster Control Station:Located at Schriever Air Force Base in ColoradoMonitoring Stations: Located in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Shriever Air Force Base Ground Control Stations:Referred to as Ground Antenna, since they are unmanned installations operated remotely
User SegmentIncludes an antenna and receiver that can provide positioning, velocity, and precise timing measurements to a user located on the ground, in the air, or over water.
How GPS WorksA GPS receiver's job is to locate four or more of these satellites, figure out the distance to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration.
TrilaterationThe basis of GPS is "trilateration" from satellites. To "trilaterate," a GPS receiver measures distance using the travel time of radio signals. To measure travel time, GPS needs very accurate timing which it achieves with some tricks
TrilaterationAlong with distance, you need to know exactly where the satellites are in space. High orbits and careful monitoring are the secret. Finally you must correct for any delays the signal experiences as it travels through the atmosphere.
Trilateration Knowing that we're 12,600 miles from a particular satellite narrows down all the possible locations we could be in the whole universe to the surface of a sphere that is centered on this satellite and has a radius of 12,600 miles.12,600 miles
12,600 miles16,000 milesThe intersection of two spheresis a circleA second measurement narrows our position down to the intersection of two spheres - an imaginary circleTrilateration
Intersection ofthree spheresis only two points16,000 miles12,600 miles14,000 milesA third measurement narrows our possible position to just two pointsTrilaterationTrilateration
TrilaterationWe can discard one pointOne point will be a ridiculous answerout in spaceor moving at high speedBut we do need a 4th measurement for a technical reason we will talk about laterIn practice 3 measurements are enoughTrilateration
Fourth measurement will decide between two pointsFourth measurement willonly go through one of thetwo pointsTrilateration
Terms to Specify Position on GlobeLatitude: degrees north and south of equator.Longitude: degrees east and west of Greenwich, England.Meridian = line of constant longitude.Parallel = line of constant latitudeGreat circle = circle inscribed on surface by a plane passing through earths center.Universal Transverse Mercator = allows precise measurements in meters to within 1 meter
LatitudeAxis of rotationEquator Latitude
LongitudeAxis of rotationEquator
Global Coordinate SystemAll meridians are great circle arcs.All parallels, except for the equator, are small circles.
Everyday Uses for GPSLand and Sea NavigationHuntingBoating and FishingVehicle Tracking and Communication (OnStar)MappingMost new vehicles are being equipped with GPS navigation units.
Commercial Uses of GPSMilitary trackingSpace TravelAir Traffic ControlRobot and Machine GuidanceMissile GuidanceSurveying and MappingMany other Engineering Uses
GPS 72 Receiver BasicsNavigation ScreensLongitude, Latitude and UTM coordinatesWaypointsTracksRoutes
Navigation ScreensInformation Page shows signal strength and satellitesMap Page displays waypoints and tracksPointer Page compass that displays navigational direction and speed of travelHighway Page displays upcoming waypoints & travel directionActive Route Page displays active route and waypoints on route
Interface KeysQuit stops current displayOn/OffGoTo link between waypointsIn zoom inOut zoom outPage page selectionMenu menu options for each pageEnter select or enter keyRocker Key moves selection up, down, left and right
Refer to Garmin Users Guide
Time to Practice
GeocachingGeocaching is an entertaining adventure game for gps users. Participating in a cache hunt is a good way to take advantage of the wonderful features and capability of a gps unit. The basic idea is to have individuals and organizations set up caches all over the world and share the locations of these caches on the internet. GPS users can then use the location coordinates to find the caches. Once found, a cache may provide the visitor with a wide variety of rewards. All the visitor is asked to do is if they get something they should try to leave something for the cache. As of today, there are 104899 active caches in 207 countries.
Geocaching WebsitesGeocaching: The Official Global GPS Cache Hunt Site - http://www.geocaching.com/Buxleys Geocaching Waypoint - http://www.brillig.com/geocaching/Letterboxing North America - http://www.letterboxing.org/GIS Lounge - http://gislounge.com/features/aa012301.shtml
What are the rules in Geocaching?Geocaching is a relatively new phenomenon. Therefore, the rules are very simple: 1. Take something from the cache 2. Leave something in the cache 3. Write about it in the logbook Where you place a cache is up to you.
What does a Geocache Look Like?Geocaches are generally in some sort of water proof container like a rubber maid box, five gallon pail, or ammunition box. The words this is a geocache may often appear on the top with the longitude and latitude coordinates.Caches generally do not contain anything of significant value, just small items of interest or collectables. Sometimes the name of the cache will give a clue to its contents.
Geocaches around the U.S.
How to Find Geocache CoordinatesThe sites listed above have geocaching coordinates for all over the U.S.. However, geocaching.com is considered the official website for finding and logging caches. You can explore caches by zip code, state, or country. The site will provide cache names, coordinates and dates the cache was placed and last found. http://www.geocaching.com/
Using Maps with GPSNavigating areas that you dont know can sometimes be dangerous. Since GPS units will only direct you in a straight line, it is necessary to know the terrain you will be traveling. This can be done with topographic maps as well as aerial photographs.
What is a Topographic MapA map that shows the c