LD 29: How does GPS work?

in conjunction with World Space Week 2018

• started with Sputnik, scientists at MIT noticed doppler effect of signals from the russian satellite
• possible to track the satellite from the ground, conversely if we know the position of the satellite we can track the receiver
• started out for tracking submarines carrying nuclear missles
• allowed for commericial use in 1983, following Korean Air Line Flight 007
• GNSS of which GPS refers to the USA system, there is also GLONASS, Beidou
• basic idea of determining location from distance to satellites
  • accuracy of 5m
• originally limited to 100m accuracy for civilian use (selected availability)
• differential GNSS
  • less than 1m
• disabled in 2000 due to use of DGNSS
• problems with GPS
  • no signal in tunnels
  • canyon effect
  • noise due to atmospheric conditions
• combine GPS with other sensors
  • available wifi signals
  • available mobile network signals
  • accelerometer
• post processing