Topic 12: Intro to GPS

Question 0

Introduction.

Answer 0

GPS relies on signals from satellites. The satellite becomes the benchmark. And GPS receivers are used to establish points on the earth.

Question 1

GPS

Answer 1

Global Positioning System

Question 2

GPS has three parts:

Answer 2

1) space segment - satillites
2) control segment - monitoring stations like in Colorado Springs and Hawaii.
3) user segment - receivers

Question 3

Errors in GPS

Answer 3

Refraction errors
Multiparty errors - refracted from other objects
Satellite errors - weak clocks, drifts, weak geometric figure
Receivers - weak clock, internal noise
Setup errors - imperfection of centering

Question 4

Selective Availability

Answer 4

Intentional error by DOD. Eliminate by differential positioning.

No longer in affect, eliminated May 1, 2000.

Question 5

Dilution of Precision (DOP)

Answer 5

When DOP value is high - weak geometry
When DOP value is low - high geometry

Depends on the number of satellites.
DOP = 1 best precision
DOP > 20 very poor

Question 6

WAAS

Answer 6

Wide Area Augmentation System

Federal Aviation Admin (FAA) develop 25 ground base stations that collect GPS signals and determine the errors, corrections forwarded to the two master stations.
Service is free, need a WAAS device.

Question 7

Applications of GPS

Answer 7

Location
Navigation
Tracking 
Mapping 
Timing