2. What is the GPS?
Orbiting navigational satellites
Transmit
position and time data
Handheld receivers calculate
latitude
longitude
altitude
velocity
It is maintained by the US government and is
freely accessible to anyone with a GPS receiver
3. History of the GPS
1969—Defense Navigation Satellite System (DNSS)
formed
1973—NAVSTAR Global Positioning System
developed
1978—first 4 satellites launched
Delta rocket launch
4. History of the GPS
1993—24th satellite
launched; initial
operational capability
1995—full operational
capability
May 2000—Military
accuracy available to
all users
5. How does GPS work?
Measuring distance by measuring time
Satellites send coded signals indicating their position in
space and the exact time the signals are being sent
Receivers use the time it takes signal to travel from
satellite to receiver to determine distance from satellite to
receiver
Information from multiple satellites is used to determine
position through ‘triangulation’
6. Three Segments of the GPS
Space
Segment
User
Segment
Control
Segment
Ground
Antennas
Master Station
Monitor Stations
11. GPS receivers
A GPS receiver's job is to locate four
or more satellites, figure out the
distance to each, and use this
information to deduce its own
location.
Hand-held receivers for recreational use
with accuracy of 10-15 meters
Vehicle mounted receivers for navigation
or agricultural use with accuracy of < 1
meter
Backpack or tripod mounted receivers for
surveying use with accuracy of 5 – 10
centimeters
12. More about GPS receivers
Receivers require clear line-of-sight; thus, they will
not work indoors or where tall objects obscure the
sky
13. Errors
Troposphere causes delays in code and carrier
But they aren’t frequency dependent
But the errors are successfully modeled
Errors due to Multipath
Receiver noise
14. Errors
Forces on the GPS satellite
Earth is not a perfect sphere and hence uneven
gravitational potential distribution
Other heavenly bodies attract the satellite, but these are
very well modeled
Not a perfect vacuum hence drag but it is negligible at
GPS orbits
Solar radiation effects which depends on the surface
reflectivity, luminosity of the sun, distance of to the sun.
this error is the largest unknown errors source
15. DGPS
Errors in one position
are similar to a local
area
High performance GPS
receiver at a known
location.
Computes errors in the
satellite info
Transmit this info in
RTCM-SC 104 format to
the remote GPS
16. Application of GPS Technology
Location - determining a basic position
Navigation - getting from one location to another
Tracking - monitoring the movement of people and
things
Mapping - creating maps of the world
Timing - bringing precise timing to the world
17. Application of GPS Technology
Private and recreation
Traveling by car
Hiking, climbing, biking
Vehicle control
Mapping, survey, geology
English Channel Tunnel
Agriculture
Aviation
General and commercial
Spacecraft
Maritime