GPS Backgrounds Flashcards
Why is essential GPS?
For monitor events, differentiates places, support location-tailored decisions, and integral in planning and decision-making.
What are some application of GPS?
Navigation VS Surveying
GPS Navigation
GPS Surveying
What are some applications of GPS?
GPS Technology Application: When, Where, and How
Measures and creates maps
geophysical and resource surveys
Nagication: Movement between locations
Location: Establishes basic position
GPS Applications
Tracking, Timing, Applications include: military, recreation, search and rescue operations, and spacecraft
What is NAVSTAR GPS?
Navigation System and Ranging
Satellite base radio positioning and time transfer system
US Department of Defense
Began in 1973
Collaborative efforts of the US military branches
What are other satellite navigation systems?
GLONASS (Russia)
Galileo (EEUU)
IRNSS (India)
QZSS (Japan)
BeiDou-3 (China
Why 4 satellites instead of 3?
Distance calculation: Utilizes microwave radio signals
* Theoretical Sufficiency of 3 satellites
* Practical requirement for 4 Satellites
* A fourth satellite compensates for receiver’s enables precise location determination
GPS Characteristics - Cont’d
- Satellite segment
- Distribution across orbital planes
Over 24 satellites
Across 6 orbital planes - Satellites in each plane
4 satellites per plane
Return Interval
Each satellite returns every 12 hours
Altitude
Positioned at 20,200 km
Orbital Inclination
Inclined at 55 degrees
More GPS Characteristics
- Position Determination
GPS receiver calculates height along horizontal position
Satellite based positioning
3 satellites needed for position identification
Importance of fourth satellite
Required for timing error correction
Enables precise positioning
GPS Operation Satellites
GPS Satellite Arrangement
- Designed for worldwide coverage
Constellation Geometry
- 4 satellites per 6 orbital planes (4x6)
- 4 to 10 satellites visible with an elevation angle of 10-15 degrees
- Minimum 4 satellites needed to provide the accurate positioning.
GPS Operation Satellites
24 Operational Satellites
Initial Operational Capability
- Completed in July 1993
- Official announcement on December 8, 1993
-Comprises 24 operational satellites
Satellite Identification Sytems
SVN (Space Vehicle Number)
- Serial numbers for GPS satellites
PRN (Pseudo Random Noise)
- Unique code transmitted by each satellite
- Used for differentiation from other satellites
Constellation Geometry
- Visible GPS Satellites
- Elevation angle range
- Elevation angle: 10-15 degrees
GPS Segments
Space Segment
- 24 Satellite Constellation
Control Segment
- Global Network of Tracking Stations
- Master Control Station (MCS) in Colorado Springs, CO
User Segment
- Dual use system
- Serves military and civilian users
What are the GPS segments?
Control, Space, User
What are the roles of the GPS segments?
Control Segment:
- Master control station, ground Antenna
Space Segment:
- Satellite ephemiris position constants
- Clock correction factors
- Atmospheric data
- Almanac
User Segment
- Coded ranging signals
- Position information
- Atmospheric data
- Almanac
Space Segment
Component of signals
- Two sine waves, two digital codes, and navigation
Role in distance calculation
- Carriers and codes determine user-satellite distance
Navigation message
- Provides satellite coordinates over time
The transmitted signal
- Regulated by onboard atomic clocks
Atomic Clocks
Most precise timekeeping system globally
Outperforms all other clock types
More accurate than Earth’s rotation or star movements
Atomic Clocks
- GPS accuracy and signal
- Role of atomic clock: Precise regulation of GPS signal
- Atomic Clock stability: Between 10^-13 and 10^-14 per day
Time loss estimation: clock may lose 1 second in - 100 million years
Control Segment: Monitor Stations
Master Control Station (MCS)
- Central processing hub of control segment
- Continuously staffed and operated
Monitoring Station
- Equipped with high quality GPS receivers and a cesium oscillator.
- Operate unmanned
- Controlled from the MCS
Control Segment: Monitor Stations
- Outcome of processing
Predicted satellite navigation data
Satellite positions over time
Satellite clock parameters
Atmospheric Data
Satellite Almanac - Updated navigation data
Transmitted to ground control stations and then uploads it to GPS satellites via the S-band link
Control Sites
- Master Control Station
Located in Colorado Springs - Monitor Stations
- 6 from Air Force and 10 from National Geospatial Intelligence Agency
Locations: Colorado Springs, Hawaii, Kwajalein, Diego Garcia,
Ascension Island, Cape Canaveral
Ground Antennad: 4 Equipped stations
Addition NGA stations
Data transmission to MCS
Current GPS Master Control & Monitor Stations
1 master control station
16 monitor stations: Air Force (6), NGA (10), 4 ground Antenna
User Segment
- U.S. DoD GPS Services
Precise Positioning Services (PPS) - Limited to authorized users, primarily for U.S military forces.
- Standard Positioning Services (SPS)
Available to both military and Civilian Users
User Segment
User receives GPS signals to determine their positions
- GPS availability
- Accessible to all users
- No cost associated
GPS Accuracy
Dithering
- Intentional Digital Noise Introduction
- Reduces Accuracy of GPS signals
DoD
- Introduced inaccuracy via Selective Availability (SA)
- DoD receiver: Capable of eliminating this noise
Selective availability discontinuation
- Ended on May 1, 2000, by president Clinton
GPS Advantages
No direct Charge
Unlimited Users
Accuracy with selective availability
- Horizontal component: 100 meters
- Time component: 34 nanoseconds
- Accuracy improvement methos: SA, Differential Method,
Doppler Frequency
GPS Disadvantages
GPS Instrumentation: Generally Costly
Signal Obstruction Impact: Avoiding obstructions to the signals, such as, overhanging branches or structures
Underground areas, densely populated urban regions
GPS Disadvantages
Need for new skills in procedural development
Integrating GPS results with traditional Networks
