Chapter 5 - Global Navigation Satellite Systems Flashcards
What are three of four satellites used for defining positions on Earth?
- NAVSTAR Global Positioning System; 2. GLONASS; 3. Galileo; 4. Chinese Compass Satellite Navigation
This global navigation satellite system was deployed by the United States Department of Defense
NAVSTAR Global Positioning System
This global navigation satellite system was deployed by the Russian government
GLONASS
This global navigation satellite system is under development by the European Union
Galileo
This global navigation satellite system is under development by China
Chinese Compass Satellite Navigation
This was the first global navigation satellite system
NAVSTAR Global Positioning System
How many phases were there in the development of NAVSTAR?
3
When was the first phase of NAVSTAR?
1973-1979
What two things occurred during Phase 1 of NAVSTAR?
Concept validation and first satellite launch
What year was the first NAVSTAR satellite launched?
1978
When was the second phase of NAVSTAR?
1979-1985
What occurred during Phase 2 of NAVSTAR?
Full development and testing
When was the third phase of NAVSTAR?
1985-present
What occurred during Phase 3 of NAVSTAR?
Production and deployment
What two levels of service does GPS provide?
Precise positioning and standard positioning systems
This level of GPS is available only to authorized users
Precise positioning system
Who is an authorized precise positioning system user?
US/allied military forces
What are two things that precise positioning systems require for use?
Cryptographic equipment and special receivers
Precise positioning systems are accurate to how many meters 95% of the time?
21 meters
This type of positioning system is available to all users
Standard positioning system
Standard positioning system accuracy was degraded by this until May 2000
Selective availability
Is the standard positioning system now roughly the same accuracy as precise positioning system?
Yes
What are the three segments of GPS?
Satellite segment, control segment, user segment
This GPS segment is a constellation of orbiting space vehicles
Satellite segment
This GPS sector is a network of ground stations
Control segment
This GPS segment is comprised of public and private users
User segment
How many active satellites make up the GPS?
31
How many inactive spare satellites are in the GPS?
2
At what height do the GPS satellites orbit?
20,000 km
How many orbital planes are in the GPS?
6
How many satellites are in each GPS orbital plane?
5
How many times per day do GPS satellites orbit?
Twice
GPS satellites contain these for positioning
Precise clocks
What are at least three of four types of navigation information constantly transmitted by GPS satellites?
- Pseudo-random ID code; 2. Time; 3. Ephemeris (precise orbit for the satellite); 4. Almanac (status information for constellation)
GPS satellites are tracked by these
USAF monitor stations
To what location is GPS data sent?
Schriever Air Force Base, Colorado
What are at least two of three regular navigational updates sent by each GPS satellite?
- All satellite clocks synchronize; 2. Ephemeris of each satellite is adjusted; 3. Health status of each satellite is given
How much money has the Department of Defense invested in GPS?
$19 billion
Since what year has the Dual Use System been in place for both civilians and military?
1985
What percent of GPS users are now civilians?
95%
What are at least two of three requirements for users to receive GPS?
Antenna, processors, stable clock
What are at least two of three factors to consider when determining surface position using GPS?
Range distance triangulation, dilution of precision, positioning errors
This uses distance from many reference points to pinpoint a location
Triangulation
What does GPS use as reference points for triangulation?
Satellites
These two types of data provide accurate satellite locations in range distance triangulation
Almanac and ephemeris data
Transmitted signals between satellites are used to determine this
Range distance
How many reference locations does triangulation use to position a point?
3
This is the distance between a satellite and a receiver
Range distance
The range distances from many satellites determines this
Receiver position
How many atomic clocks does each GPS satellite have?
4 (2 cesium and 2 rubidium)
What is the accuracy of GPS satellite clocks?
+/- 1 second per $30,000
How much does each GPS satellite clock cost?
$100,000-$500,000
GPS receiver clocks are similar to these
Quartz watches
Is there never error between satellite and receiver clocks?
No
Can atomic clocks be used in GPS receivers?
No
What size are the atomic clocks in GPS satellites?
Computer-size
Are GPS receiver clocks accurate only over short periods?
Yes
Do GPS receiver clocks need to be reset often?
Yes
Which satellite is used to recalibrate the receiver clock?
4th satelllite
This is the measure of geometry of visible satellites
Dilution of precision
Does high dilution of precision result in good or poor satellite spread?
Poor satellite spread
Does high dilution of precision result in high or low positional uncertainty?
High positional uncertainty
Does low dilution of precision result in good or poor satellite spread?
Good satellite spread
Does low dilution of precision result in high or low positional accuracy?
Low positional accuracy
What does PDOP stand for?
Position dilution of precision
What does VDOP stand for?
Vertical dilution of precision
What does HDOP stand for?
Horizontal dilution of precision
What DOP value is considered ideal?
1
What DOP value is considered very good?
1-3
What DOP value is considered good?
4-5
What DOP value is considered fair?
6
What DOP value is considered suspect?
> 6
What are at least 4 of 7 sources of positioning errors?
- Selective availability; 2. Satellite and receiver clock errors; 3. Ephemeris errors; 4. Atmospheric interference; 5. Receiver computation/noise; 6. Multipath errors; 7. Interference from radar/microwave/radio waves
This is the intentional degradation of GPS for national security
Selective availability
Selective availability results in how many meters of positioning error?
100 m (160 m vertical)
When was selective availability of GPS turned off?
May 2000
Satellite and receiver clock errors result in how many meters of positional errors?
1 m
Ephemeris errors result in how many meters of positioning errors?
1 m
Atmospheric interference results in how many meters of positioning errors?
10 m
Multipath errors result in how many meters of positioning errors?
0.5 m
Positioning errors create this in range distance
Range uncertainty
These errors can be reduced with a special antenna and receiver
Multipath errors
This is an enhancement to GPS that was created to improve the low accuracy by selective availability
Differential GPS
Differential GPS uses this at known points
Ground station network
DGPS stations asses satellite error by measuring differences between these two positions
Known and satellite-calculated position
DGPS uses range measures from these two sources
Roving receiver and base station
In DGPS, these are used to correct positions for the roving receiver
Base stations
What is the positioning accuracy of GPS without DGPS?
10 m
What is the positioning accuracy of DGPS?
2 cm - 2 m
DGPS has the best results when the rover is within this many km from a base station
300
In this form of DGPS, rover and base station data are put into a computer, then corrections applied to rover data
Post-processed DGPS
In this form of DGPS, base stations transmit corrections made on the fly to a rover
Real-time DGPS
How many stations are in the U.S. national DGPS network?
82 (128 planned)
What are two kinds of GIS receivers?
Code-phase receivers and carrier-phase receivers
These GIS receivers’ measurements use transmitted pseudo random code
Code-phase receivers
What is the error range in meters for a single fix for a code-phase GIS receiver?
3-30 m
Can code-phase receivers occasionally have errors greater than 100 m?
Yes
How can accuracy be improved for code-phase GIS receivers?
By averaging many fixes
These GIS receivers’ measurements use satellite carrier waves
Carrier-phase receivers
What is the accuracy of carrier-phase GIS receivers?
A few cm
These GIS receivers require continuous data collection over a long period
Carrier-phase receivers
What is the accuracy of low-cost SPS GIS receivers?
100 m
What is the accuracy of medium-cost DGPS SPS GIS receivers?
1-10 m
What is the accuracy of high-cost DGPS carrier-phase GIS receivers?
1 mm - 1 cm
What are at least two of three applications of GPS in the field?
- Field digitization; 2. Tracking/navigation; 3. Land surveying
This type of data can be recorded directly in the field with GPS
Vector data
Can attributes be obtained in the field from GPS?
Yes
GPS data can be used to establish these in field digitization
Control points
New field digitization GPS equipment combines these two devices to integrate data straight into GIS
Receiver and computer
These aid in point collection during field digitization
Laser rangefinders
Field GPS data collection can be hampered by this
Sky obstruction
At what angle above the horizon does terrain become a serious problem in field digitization?
> 15 degrees
What are two types of equipment to help field digitization equipment in difficult terrain?
Advanced receivers and range poles
Real-time GPS tracking is used for managing these
Vehicle fleets
New GPS receivers can be used to track this in the field
Wildlife
GPS receivers can aid this in the land, sea and air
Navigation
