Lecture 5 Global Positioning Systems

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Questions and Answers

What is the primary reason GPS requires four satellites to fix a 3D position?

To compute altitude through trilateration. (correct)

To enhance precision in signal processing.

To account for temporal offsets.

To determine latitude and longitude.

Which segment is NOT a part of the GPS system?

User segment

Space segment

Monitoring segment (correct)

Control segment

The operational management of GPS is carried out by which organization?

NASA

US Department of Defence (correct)

National Oceanic and Atmospheric Administration

Federal Aviation Administration

How is the concept of trilateration applied in GPS positioning?

By determining the distance from multiple satellites to intersect a point. Signup and view all the answers

What is one of the main uses of GPS in research projects?

Measuring atmospheric parameters. Signup and view all the answers

Where is the Master Control facility located?

Schriever AFB in Colorado Springs Signup and view all the answers

What is the primary function of a GPS receiver?

To convert satellite signals into position, velocity, and time estimates Signup and view all the answers

How many satellites are needed to compute position and time accurately?

Four Signup and view all the answers

What process is used to determine a user's position in GPS?

Trilateration Signup and view all the answers

What happens when the distance to three satellites is known during trilateration?

One point is usually rejected due to impossibility. Signup and view all the answers

Which of the following is NOT a component of the User Segment?

Satellites Signup and view all the answers

What is utilized by the Master Control station to enhance satellite performance?

Ephemeris and clock data Signup and view all the answers

What is a common application for GPS receivers?

Navigating and positioning Signup and view all the answers

What is GPS primarily designed for?

Global positioning and navigation for various users Signup and view all the answers

Which segment of GPS is responsible for sending signals from space?

Space Segment Signup and view all the answers

How many satellites constitute the GPS operational constellation?

24 Signup and view all the answers

What altitude do GPS satellites orbit the Earth?

20,200 km Signup and view all the answers

What does the Control Segment of GPS consist of?

Tracking stations around the world Signup and view all the answers

Which component of GPS is critical for synchronizing time for accuracy?

The satellites' atomic clocks Signup and view all the answers

What type of signals do GPS satellites provide for computation?

Specially coded satellite signals Signup and view all the answers

What is the purpose of having multiple satellites visible from any point on Earth?

To enable accurate position calculations in three dimensions Signup and view all the answers

How can the distance from a satellite to a receiver be calculated using a radio signal?

Distance = Velocity x Time Signup and view all the answers

What is the speed of radio waves as they travel through space?

186,000 miles/second Signup and view all the answers

What is necessary for the GPS system to determine accurate locations?

The clocks of the satellite and receiver must be perfectly synchronized. Signup and view all the answers

How does GPS correct for differences in time between the receiver and satellite?

Through iterative adjustments until a unique solution is found. Signup and view all the answers

What role does the fourth satellite play in the GPS system?

It allows the receiver to synchronize its clock. Signup and view all the answers

Why is accuracy in satellite timekeeping crucial for GPS technology?

It affects the calculation of travel time and distance. Signup and view all the answers

What is the consequence of a clock error in the GPS receiver?

It alters the calculated position to a wrong point. Signup and view all the answers

How does the receiver ultimately achieve the precision required for positioning?

By continuously iterating until a unique intersecting point is found. Signup and view all the answers

Study Notes

Introduction to Global Positioning Systems (GPS)

GPS is a satellite navigation system.
It's also known as the Navstar system.
It's a satellite navigation system that provides timing and ranging signals.
GPS is funded and managed by the U.S. Department of Defense (DOD).
Millions of civilian users employ GPS worldwide; however, the system was originally designed and is operated by the US military.

Presentation Outline

Definition and background of GPS
Components and segments of GPS
How GPS works
Synchronization of time for atomic clock accuracy
Uses of GPS

Components and Segments of GPS

GPS system comprises three segments: space, control, and user segments
Space Segment: Consists of the GPS satellites (also called space vehicles (SVs)). These satellites continually transmit radio signals from space. Currently, there are 24 satellites in operation in the GPS constellation that orbit Earth every 12 hours. New satellites are launched and placed in reserve, ready to replace older satellites.
Control Segment: A system of monitoring stations is positioned around the globe. The master control facility is located at Schriever Air Force Base (AFB) in Colorado Springs, and an alternative master control station is at Vandenberg Air Force Base in California. Four additional monitoring stations are tasked with measuring signals coming from the satellites, which data is used in developing orbital models for each satellite.
User Segment: Comprises GPS receivers and their users. GPS receivers translate satellite signals into position, velocity, and time estimations. Four satellites are essential for computing the four dimensions (X, Y, Z, and time). These receivers are employed for navigation, positioning, disseminating information and other research.

How GPS Works

GPS utilizes trilateration to accurately find a location.
With one satellite a unique location is not possible as one is positioned on a sphere around the satellite.
Two satellites help to determine the location where two spheres intersect.
Three satellites determine the correct position as the three intersecting spheres give two points.
GPS measures distance via a radio signal from satellite to receiver.
Distance = Velocity × Time
Pseudo-Range = Speed of Light × Travel Time.
Radio waves travel at the speed of light.
The difference in the time taken to send and receive a signal is used to determine the distance.

Synchronization of Time

Satellites have highly precise atomic clocks.
GPS receivers have less precise clocks.
Accurate timing is crucial for positioning.
A fourth satellite is used to adjust receiver time iteratively till a unique position is determined.

Uses of GPS

Providing precise positioning and corrections at reference locations.
Surveying, geodetic control and plate tectonic studies are made possible using data.
Time and frequency distribution uses the accurate clocks in satellites.
Astronomical observatories, telecommunications facilities.
Researching atmospheric parameters and earthquakes/landslides.
Search, rescue, and navigation operations.

Lecture Summary

GPS is a satellite navigation system created by the US Department of Defense.
It involves three segments (space, control, user).
GPS uses trilateration and determines distances that are based on atomic clock accuracy.
A fourth satellite is used to adjust the receiver time so an accurate location can be calculated.

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Description

This quiz covers the fundamentals of Global Positioning Systems (GPS), including its definition, components, and how it operates. Learn about the space, control, and user segments that make up the GPS network, along with its military origins and civilian applications.