The Global Positioning System and Its Components

Flashcards on the Fundamentals of Remote Sensing and Geographic Information System - Topic 9: The Global Positioning System and Its Components.

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