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?

<p>By determining the distance from multiple satellites to intersect a point. (D)</p> Signup and view all the answers

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

<p>Measuring atmospheric parameters. (D)</p> Signup and view all the answers

Where is the Master Control facility located?

<p>Schriever AFB in Colorado Springs (C)</p> Signup and view all the answers

What is the primary function of a GPS receiver?

<p>To convert satellite signals into position, velocity, and time estimates (D)</p> Signup and view all the answers

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

<p>Four (C)</p> Signup and view all the answers

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

<p>Trilateration (D)</p> Signup and view all the answers

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

<p>One point is usually rejected due to impossibility. (B)</p> Signup and view all the answers

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

<p>Satellites (B)</p> Signup and view all the answers

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

<p>Ephemeris and clock data (C)</p> Signup and view all the answers

What is a common application for GPS receivers?

<p>Navigating and positioning (D)</p> Signup and view all the answers

What is GPS primarily designed for?

<p>Global positioning and navigation for various users (C)</p> Signup and view all the answers

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

<p>Space Segment (A)</p> Signup and view all the answers

How many satellites constitute the GPS operational constellation?

<p>24 (C)</p> Signup and view all the answers

What altitude do GPS satellites orbit the Earth?

<p>20,200 km (C)</p> Signup and view all the answers

What does the Control Segment of GPS consist of?

<p>Tracking stations around the world (D)</p> Signup and view all the answers

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

<p>The satellites' atomic clocks (C)</p> Signup and view all the answers

What type of signals do GPS satellites provide for computation?

<p>Specially coded satellite signals (A)</p> Signup and view all the answers

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

<p>To enable accurate position calculations in three dimensions (B)</p> Signup and view all the answers

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

<p>Distance = Velocity x Time (A)</p> Signup and view all the answers

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

<p>186,000 miles/second (D)</p> Signup and view all the answers

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

<p>The clocks of the satellite and receiver must be perfectly synchronized. (C)</p> Signup and view all the answers

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

<p>Through iterative adjustments until a unique solution is found. (D)</p> Signup and view all the answers

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

<p>It allows the receiver to synchronize its clock. (B)</p> Signup and view all the answers

Why is accuracy in satellite timekeeping crucial for GPS technology?

<p>It affects the calculation of travel time and distance. (B)</p> Signup and view all the answers

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

<p>It alters the calculated position to a wrong point. (B)</p> Signup and view all the answers

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

<p>By continuously iterating until a unique intersecting point is found. (C)</p> Signup and view all the answers

Flashcards

GPS

A satellite navigation system developed by the US Department of Defense for military purposes but with global civilian use.

Space Segment

A network of satellites orbiting Earth that transmit signals to GPS receivers.

Control Segment

A system of ground stations that track the satellites, control their orbits, and ensure accurate timing.

GPS Receivers

Devices that receive signals from GPS satellites and calculate your position, velocity, and time.

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Pseudo Ranges

Coded signals sent by GPS satellites that allow receivers to calculate distances and time.

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Time Synchronization in GPS

The process of ensuring that all clocks in a system, including satellites and receivers, are perfectly synchronized.

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GPS Accuracy

The level of accuracy of GPS measurements, which can be influenced by factors like satellite visibility and atmospheric conditions.

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Uses of GPS

Various applications of GPS technology like navigation, mapping, surveying, and timing.

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Master Control Station

The primary ground-based component of the GPS system, responsible for tracking and managing the orbiting GPS satellites.

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Monitoring Stations

Auxiliary ground stations that assist the Master Control Station by measuring signals from the GPS satellites to refine their orbital data.

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Ephemeris

The comprehensive set of data that describes a satellite's precise location and movement in space.

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Data Uploading

The process of transmitting corrected ephemeris and clock data from the Master Control Station to the GPS satellites.

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User Segment

The collection of GPS receivers used by individuals, organizations, and various systems to access and utilize the GPS signals.

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Trilateration

The technique GPS receivers use to determine their location by calculating the distances to multiple satellites.

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Time Difference

The concept of using the time difference between signals received from multiple satellites to calculate the distance to each satellite.

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Position Calculation

The act of calculating the user's position, using signals from four GPS satellites to determine the three spatial coordinates (X, Y, Z) and the time.

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How is distance to a GPS satellite calculated?

The distance from a GPS satellite to a receiver is calculated by multiplying the speed of light by the time it takes for a radio signal to travel between them.

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What is the approximate travel time for a signal from a directly overhead satellite?

If a satellite is directly overhead, the time taken for a radio signal to travel from the satellite to a receiver is approximately 0.06 seconds.

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How do GPS satellites transmit unique codes?

Each GPS satellite transmits a unique code that changes over time, relative to the satellite's internal atomic clock.

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How does a GPS receiver use the satellite code?

The receiver also generates the same pseudo random code, synchronized to its own clock. By comparing the received code to its own code, the receiver can calculate the time difference.

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Why is accurate timing important in GPS?

GPS requires accurate timing in order to work. The receiver's clock is not as accurate as the satellite's, so a method is needed to synchronize them.

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What is the fourth satellite principle?

The fourth satellite principle is a technique used in GPS to synchronize the receiver's clock with the highly accurate atomic clocks on the satellites.

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How does the fourth satellite principle work?

Because the receiver's clock is not perfectly synchronized with the satellite's clock, the calculated distances to the satellites will be inaccurate. The fourth satellite principle uses this inconsistency to correct the receiver's clock.

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What is the outcome of the fourth satellite principle?

The fourth satellite principle essentially allows the GPS receiver to utilize the accurate time information from the satellites, effectively transforming the receiver's inexpensive clock into an atomic clock.

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How does GPS determine your position?

GPS uses trilateration, a technique that involves calculating distances to multiple satellites to determine position. At least four satellites are required to solve for a 3D position (latitude, longitude, and altitude).

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How does GPS measure distance?

The time difference between the signal transmitted by the satellite and received by the GPS receiver is used to determine the distance between them. This is done by comparing the receiver's clock with the atomic clock onboard the satellite.

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What are some uses of GPS beyond navigation?

GPS signals are used for applications beyond navigation, including surveying, geodesy, time synchronization, and research projects like measuring atmospheric parameters.

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What is the role of the control segment in GPS?

The control segment of GPS consists of ground stations that manage the satellites, including monitoring their orbits, ensuring accurate timing, and sending updates.

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Why are four satellites needed for accurate GPS?

The fourth satellite in GPS helps to synchronize the time on the receiver. This is done through iterative clock adjustment until a unique position fix is achieved, ensuring accurate positioning.

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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.

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