Global Navigation Satellite Systems Flashcards
The standard generic term for satellite navigation systems that provide autonomous geospatial positioning with global coverage
GNSS
Three segments of GNSS
satellites, ground station, and users
Define these 3:
1. Space
2. Control
3. User
- Constellation of satellites orbiting the Earth
- Tracks and monitors the satellites
- Rely on the satellites to compute for their position and motion
- Operated by the Department of Defense (DoD), USA
- Based on a constellation of 24 to 32 satellites
- Orbits 22,000 km above the Earth along 6 orbital planes
- Two services: Precise Positioning Service (PPS) and Standard Positioning Service (SPS)
Global Positioning System (GPS)
- Operated by the Russian Aerospace Defense Forces, Russia
- Has 24 satellites distributed in 3 orbital planes at a similar altitude as GPS satellites
- Provides better coverage at higher latitudes compared to other GNSS
- Currently broadcasts on two frequencies but will expand to three in future satellite launches
Globalnaya Navigazionnaya Sputnikovaya Sistema (GLONASS)
- Operated by the China National Space Administration, China
- Sometimes called COMPASS and has both regional and global satellites in space
BeiDou
- Operated by the European Space Agency, Europe
- It started offering Early Operation Capability (EOC) on 15 Dec 2016, providing initial services with weak signal and is expected to reach Full Operational Capability (FOC) in 2020
- When complete, it will consist of approximately 30 satellites transmitting signals in several frequencies that overlap with other GNSS
- Will be interoperable with GPS and GLONASS
Galileo
- A Japanese satellite position system operated by the Japan Aerospace Exploration Agency (JAXA)
- Also known as “MICHIBIKI” and was launched on 11 Sep 2010
- Operated as a four-satellite constellation from Nov 2018 and three satellites are visible at all times in the Asia-Oceania region
- QZSS can be used in an integrated way with GPS, bringing more number of satellites to users
Quasi-Zenith Satellite System
- An independent regional navigation satellite system being developed by the Indian Space Research Organization (ISRO) with positional accuracy of <20 m
- 3 satellites in geostationary orbit, 4 satellites in geosynchronous orbit, and 2 planned spare satellites
- Two services to be provided: Standard Positioning Service (SPS) for all users and Restricted Service (RS) for authorized users
Indian Regional Navigation Satellite System
How GNSS Receivers Work?
Knows where each satellite is in its _________ and compares it with the time required to receive each satellite’s signal
orbit
Difference between triangulation and trilateration
Triangulation measures angles while trilateration involves measuring distances
A well designed receiver can achieve a horizontal accuracy of A.) __ meters or better and a vertical accuracy of B.) __ meters or better 95% of the time
A.) 3
B.) 5
Augmented GNSS can provide _________ accuracy
sub-meter
Are locations or landmarks that are recorded and stored in your receiver or device
Waypoints
Is a set of coordinates connected together and their associated data (e.g., elevation, time, distance, etc.)
Track
Is a pre-determined path created from a group of location of points entered into the device in the sequence you desire to navigate them
Route
Describes error caused by the relative position of the GNSS satellites
More signals a GNSS receiver can “see”, the more precise it can be
Position/Geometric Dilution of Precision (PDOP or GDOP)
Atmosphere Refraction
Troposphere and ionosphere can change the speed of _________ of a GNSS signal
propagation
Multipath Effect
Occurs when the GNSS satellite signal _________ off of nearby structures like buildings and mountains
bounces
Satellite Time and Location (Ephemeris)
Accuracy of a GNSS satellite’s atomic clock is one _________
nanosecond
Satellite Time and Location (Ephemeris)
__________________ contains details about the specific satellite’s location
Ephemeris information
Two ways to improve accuracy?
- Differential GPS (DGPS)
- Satellite-Based Augmentation System (SBAS)
Differential GPS (DGPS)
- Involves the cooperation of two _________, one that’s stationary and another that’s roving around making position measurements
- Two receivers track the same signal and errors at the same time
receivers
Satellite-Based Augmentation System (SBAS)
- Rely on networks of base stations on the ground to monitor GPS satellites
- Broadcasts correction signals from __________________ rather than directly to users
geostationary satellites
