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Flashcards on the Fundamentals of Remote Sensing and Geographic Information System - Topic 9: The Global Positioning System and Its Components.
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Sputnik 1
The first artificial Earth satellite launched into space by the Soviet Union (USSR) in 1957, initiating the Space Race.
NAVSTAR GPS Project
Initiated by the US in 1973, aiming to launch 24 satellites for positioning and navigation, becoming fully operational by 1995.
GPS (Global Positioning System)
A space-based satellite navigation system providing location and time information in all weather conditions, maintained by the United States government and freely accessible with a GPS receiver.
Space Vehicle Number (SVN) or Pseudorandom Noise (PRN) code
Methods used to identify GPS satellites.
GPS Components
Consist of three major segments: Space Segment (satellites), Control Segment (ground control stations), and User Segment (receivers).
Control Segment Entities
Made up of three entities: Master Control System, Monitor Stations and Ground Antennas.
Master Control Station Location
Located at Falcon Air Force Base in Colorado Springs
GPS Receiver Function
Receives radio signals from satellites, calculates the signal travel time, and computes its geographic location.
GPS Positioning Geometry
Once a GPS receiver knows its distance from at least 4 satellites, it uses geometry to determine its exact location on Earth in 3D.
GPS Atomic Clocks
Used in GNSS satellites to keep very precise time, while GPS receivers use less accurate crystal clocks.
P-code
A precise GPS code available to the military and selected US public officials.
C/A code
A less precise GPS code available for civilian use; also called Civilian code.
L1 Frequency
The frequency (1,575.42 MHz) on which the C/A code is transmitted.
L2 Frequency
The frequency (1,227.60 MHz) on which the Precision code is transmitted.
GNSS Errors
Include satellite clock errors, orbit errors, ionospheric delay, tropospheric delay, multipath errors, and receiver noise.
Satellite Clock Error Implications
A time difference between the satellite clock and the receiver clock causing errors
Ionospheric Delay
When electrically charged particles in the ionosphere interact with the satellite signal and causes its delay, resulting in satellite position error.
Multipath (MP) Error
Occurs when a signal is reflected off an object to the GNSS antenna, causing inaccurate distance measurements and position calculations.
Signal to Noise Ratio (SNR)
The ratio of the signal power and noise power in a given bandwidth. GNSS receiver with high SNR are recommended to avoid receiver noise
Differential GPS (DGPS)
A technique to improve GPS performance using a fixed GPS receiver (base station) to correct errors in rover GPS receivers.
Real-Time Kinematic (RTK)
A positioning technique similar to DGPS, aiming to reduce and remove errors common to a base station and rover pair.
Precise Point Positioning (PPP)
A positioning technique that removes or models GPS system errors to provide high position accuracy from a single receiver, without needing local reference stations.
Satellite Based Augmentation System (SBAS)
Enhances position accuracy by providing services for improving the accuracy, integrity, and availability of GPS signals using geosynchronous satellites and ground-based infrastructure.
Ground Based Augmentation System (GBAS)
Provides differential corrections and satellite integrity monitoring to receivers using a VHF radio link, commonly used in airports for high accuracy.
Different Grades of GPS Receivers
Recreational Grade, Mapping Grade, and Survey Grade
MultiPath Errors
Try and stay away from buildings, trees and other structures when using a GNSS receiver
Common GPS Applications
Consumer, Transportation, Precision Agriculture, Construction, Mining, Surveying and Research/projects that require location mapping