SURV1200 Lecture Notes - Lecture 8: Differential Signaling, Error Analysis For The Global Positioning System, Differential Gps
2 Jun 2018
School
Department
Course
Professor
SURV 1200
Introduction into Surveying
8.GPS
Global navigation satellite systems (GNNS) can be used, focus on global positioning system
(GPS)
The US Defense Force developed GPs in the nineteen eighties to focus on positions
The basics
o GPS Coleman Global positioning system
o Satellites currently over 32 satellites, in 20000 km orbits
o Ground Control stations-track and control the satellites
o GPS receives-used to calculate position on earth
o The satellites - orbits provide the user with several satellites are visible from only one
place on Earth
Each satellite puts out two or more signals
o L1 1575.4 MHz at a wavelength of 0.9 m
o L2 1227.6 MHz at a wavelength of 0.24 metres
Each satellite is a precise clock sending out continuous identifications
Satellite code
L1
L2
C/A code
P Code
navigation message
P code
navigation message
C/A code-course acquisition or Kim code
3 to 30 m of accuracy at a wavelength of 300 m
P code-precise code is all military use only and has a much better accuracy at a wavelength of 30
meters. The peacoat is encrypted anti-spoofing
Selective availability-deliberately degrade the CIA code by introducing errors in The Signal.
This was turned off in May 2000, but can be reactivated it anytime
find more resources at oneclass.com
find more resources at oneclass.com
Global navigation satellite system
Systems
o Glosnass -Russian 24 satellites
o Galileo -Europe 28 satellites
o Compass -China 38 planned satellites
The ground stations compute precise orbital data and clock corrections for each satellite, and the
data is uploaded to the satellites.
Receivers
Navigation: receive it in aircraft, chips, ground vehicles, use the satellite signals to determine
position, and velocity
Surveying: receivers are a bit different. Some details-must see Sky, microwave signals can't
penetrate buildings, or objects.
Satellite signals: -if satellite continuously broadcast the time, and its orbital data-each satellite
transmits these times signals on more than one frequency.
By accuracy measuring distances from at least three satellites, we can deduce over 3D position
anywhere on earth.
Trilateration-intersection of distances. Two spheres intersect producing a circle. Allocation
could be anywhere on the circle.
Three spheres intersect at 2 points only. One will make sense and the other will be significantly
off the surface of the earth full
The GPS receive measure distance using the travel time of the radio signal.
Each satellite sends a unique code which is timestamped when it leaves the satellite. Receiver
compares the satellite time when the signal was admitted, with the receiver time when the signal
is received. The receiver then uses the time difference to calculate a distance (called pseudo
range closed parentheses
Distance = velocity x change in time where, velocity equals 299274 km per second
-accurate timing is the key to measuring the distances to the satellites.
-satellites have precise atomic clocks that are very stable
-receive a clock so often less accurate than atomic clocks in satellites
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Global navigation satellite systems (gnns) can be used, focus on global positioning system (gps) The us defense force developed gps in the nineteen eighties to focus on positions. Each satellite puts out two or more signals: l1 1575. 4 mhz at a wavelength of 0. 9 m, l2 1227. 6 mhz at a wavelength of 0. 24 metres. Each satellite is a precise clock sending out continuous identifications. 3 to 30 m of accuracy at a wavelength of 300 m. P code-precise code is all military use only and has a much better accuracy at a wavelength of 30 meters. Selective availability-deliberately degrade the cia code by introducing errors in the signal. This was turned off in may 2000, but can be reactivated it anytime. Systems: glosnass -russian 24 satellites, galileo -europe 28 satellites, compass -china 38 planned satellites. The ground stations compute precise orbital data and clock corrections for each satellite, and the data is uploaded to the satellites.
