GPS - Aircraft Navigation

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THIS DAY IN AVIATION November 21 1783 — The first free or untethered human flight takes place when Jean Francois Pilatre de Rozier flies as high as 500 feet and travels 5 miles over Paris in a Montgolfier hot-air balloon.

THIS DAY IN AVIATION November 21 1957 — The first of several ballistic missile bases to be erected at Francis E. Warren AFB, Wyoming.

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November 2017 Chap 5 Quiz FLIGHTLINE 5 6 Chapter 5 SUNDAY MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY 5 6 Chapter 5 Military Developments Separate Air Force Wartime Advances 7 Jet Propulsion “Vengeance Weapons” Helicopters 8 Berlin Airlift 9 Korean War Lessons Learned 10 Chap 5 Quiz FLIGHTLINE 11   12 13 Commercial Aviation General Aviation 14 Aviation R & D 15 Vietnam War Phase 1 and 2 16 Phase 3 and 4 17 Chap 5 TEST 18 19 20 21 22 NO SCHOOL 23 THANKSGIVING 24 25 26 27 Chapter 6 Advances in Aeronautics 28 29 Chap 6 TEST 30 1 2

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GPS – Aircraft Navigation Teams will exchange coordinate charts with item description. (Listed on Board) Final report will be Powerpoint with pictures of waypoint locations and items. Title Slide with Team name, Individual names Slide with ‘Snipping Tool’ pic of plotted areas from Google Earth – all points should be labeled Selective Availability was the military degradation of the GPS accuracy for defense purposes. More information is available at the National Executive Committee for Space-Based PNT website: http://pnt.gov/public/sa/ The PRC and ephemeris signals from four satellites should provide an absolutely accurate position to the precision of the atomic clock on the satellite. The key word is “should” as there are many problems associated with timing the signal’s travel time. Remember even a thousandth of a second is a huge error!   Problems include the reduction in the speed of light as it enters the atmosphere (error to greater distance), signals that reflect off of multiple objects and create echoes that arrive at different times, purposeful errors, and even atomic clock errors. We can correct for the atmospheric problems by using more advanced technology. If the receiver can monitor dual frequencies, then it can compare the amount of variation between a low-frequency (slowed more) and a high-frequency (slowed less) signal to deduce the error and correct for it. The GPS system broadcasts on two different carrier frequencies called L1 and L2. Unfortunately, this requires a very sophisticated receiver. Only the military has access to the L2 carrier channel. The other option is to build in atmospheric models so that “typical” corrections can be made to all incoming signals. Receivers can deal with the multi-path errors by employing signal rejection analysis software. The basic principle is that the first signal to arrive will have traveled along the shortest route and thus any signal that arrives later is most likely an echo and should be ignored. Before May 1, 2000, the government purposely degraded the timing data of the satellite’s clock by adding noise to the signal. They may also have introduced slight inaccuracies to the ephemeris data. Military GPS receivers made use of a decryption key to obtain the full accuracy information. This Selective Availability (SA) was disabled, which improved the accuracy of GPS positions by a factor of 10. All of these errors combined introduced errors of about 10 meters. With SA active, this led to errors of hundreds of feet. Without SA the basic GPS receiver is capable of measuring positions to within 30 or 50 feet. This is accurate enough for an aircraft approaching a runway, but unfortunately it isn’t accurate enough to land the aircraft on the centerline of the runway.

GEO CACHE MAPPING GOOGLE EARTH

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