Title: GPS Global Positioning System The system was designed for and is operated by the U'S' military
1GPS (Global Positioning System) The system
wasdesigned for and is operated by the U.S.
military
Geology
2GPS Space Segment
24 operational satellites (SVs) that orbit Earth
in 12 hours Repeat almost same ground track once
each day 6 orbital planes with 4 SVs in each In
theory, 5-8 SVs visible from any point on Earth
Geology
3GPS Control Segment
Master Control Facility Schriever AFB
(formerly Falcon AFB) Uploads ephemeris (precise
orbital position) and clock data to the
SVs Monitor stations measure signals from
SVs which are incorporated into their orbital
models
Geology
4GPS User Segment
Position is where pseudo-ranges from a set of SVs
intersect
GPS receivers convert SV signals into position,
velocity, and time estimates 4 SVs required to
compute the four dimensions (X,Y,Z,t)
Geology
5Receiver Position
Position computed by receiver in Earth-centered,
Earth fixed X,Y,Z coordinates that are then
converted by receiver to geodetic latitude,
longitude, and height (using WGS 84 ellipsoid)
Geology
6GPS Error Sources
Combination of noise, bias, and blunders Noise
errors combined effect of PRN code noise (about
1 m) and noise within the receiver (about 1
m) Bias errors From Selective Availability
(SA) and other factors SA intentional
degradation of the signals by DOD to limit
accuracy for non-military applications (100
m) this is no longer in use Other factors for
example, ephemeris data errors (1
m), tropospheric delays (1 m), ionosphere delays
(10 m) Blunder errors just like it sounds
sometimes operator sometimes software
Geology
7Differential GPS (DGPS)
Correct bias errors at one location with measured
bias errors at a known position A reference
receiver (base station) computes corrections for
each satellite signal e.g., Coast Guard
maintains a network of differential monitors and
transmits corrections along coastline
Geology