GEOG 3315 - Module 8

Global Navigation Satellite System (GNSS)

A satellite-based positioning system composed of three components, providing continuous, worldwide positioning.

NAVSTAR GPS

A GNSS system created by the United States, providing worldwide, continuous, accurate, three-dimensional position and velocity, and precise time.

Space Segment

Part of the GPS system consisting of a constellation of satellites orbiting Earth, ensuring at least four satellites are visible above the horizon at all times.

Control Segment

Earth-based monitoring stations that track, update, and calibrate the clocks on GPS satellites.

User Segment

Composed of individuals using GPS receivers, which gather information from satellites to calculate positions.

Coarse Acquisition Code

A code broadcasted by GPS satellites used by both civilian and military sectors, providing pseudorandom code describing ephemeris data and GPS almanac.

P Code

A code used to determine the location of the GPS receiver, broadcasted over seven days, used by the civilian sector.

Ephemeris Data

Information about the location of satellites, essential for determining positions using GPS.

Differential GPS (DGPS)

A method to increase the accuracy of GPS by using a base station at a known location to broadcast corrections to a rover receiver.

Real-Time Kinematic (RTK) GPS

A differential GPS method where corrections are broadcasted in real-time using communication capabilities like radio.

Post-Processing

Applying GPS base station corrections to rover data at a later time using a computer, suitable for most situations without requiring real-time communication.

Continuous Operation Reference Stations (CORS)

A network of base stations providing real-time or post-processing GPS observations, established by the United States Coast Guard.

Wide Area Augmentation System (WAAS)

A differential positioning method using geostationary satellites and a network of reference stations to provide real-time accuracies within 7 meters or less.

Multipath Error

An error occurring when the GPS signal travels a longer distance due to bouncing off objects like buildings or trees before reaching the receiver.

Dilution of Precision (DOP)

A measure of the GPS satellite constellation geometry's effect on positional accuracy, with lower values indicating better accuracy.

Positional DOP (PDOP)

The ratio of the volume of a tetrahedron created by the most widespread satellites to the volume of an ideal tetrahedron, used to assess overall positional accuracy.

Ephemeris Error

The residual error in the satellite's exact position compared to its reported position, affecting position calculations.

Atmospheric Error

Variations in the speed of light as the GPS signal travels through the Earth's atmosphere, affecting distance calculations.

Clock Error

Discrepancies between the atomic clocks in GPS satellites and the less precise clocks in GPS receivers, affecting temporal calculations and positioning.

Field Data Collection

The process of gathering data in the field using devices like GPS receivers or smart devices with GNSS chips, often integrated with mobile mapping software.