Introduction to Global Positioning Systems
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Questions and Answers

What is the primary method used by GPS to determine the location of a receiver?

  • Ground-based triangulation
  • Satellite trilateration (correct)
  • Inertial navigation
  • Cellular triangulation

How many satellites are needed to determine a precise location using trilateration?

  • One satellite provides a general area.
  • Two satellites can pinpoint a location on a line.
  • Three satellites are required for an exact position. (correct)
  • Four satellites are needed regardless of conditions.

What formula is used to calculate the distance to a satellite in GPS technology?

  • Distance = Time x Acceleration
  • Distance = Time / Speed
  • Distance = Speed of Light x Travel Time (correct)
  • Distance = Velocity + Time

What is the speed of radio waves as used in GPS measurement?

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

Why is a very accurate clock necessary in GPS technology?

<p>To calculate travel time accurately (D)</p> Signup and view all the answers

What is required for the GPS system to calculate accurate positioning?

<p>Synchronization of the satellite and receiver clocks (B)</p> Signup and view all the answers

How does GPS address the inaccuracies of a receiver's clock?

<p>By implementing a correction process involving a fourth satellite (A)</p> Signup and view all the answers

Why is a fourth satellite necessary in GPS systems?

<p>To account for positioning in a 3D space (D)</p> Signup and view all the answers

What happens when the receiver's clock is slower by one second?

<p>The GPS calculations will converge at the wrong point (D)</p> Signup and view all the answers

Which component of the GPS system has very accurate timekeeping capabilities?

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

How do GPS receivers determine the clock error during positioning?

<p>By adjusting until a unique solution is found (D)</p> Signup and view all the answers

What is one of the uses of GPS mentioned in the content?

<p>Monitoring atmospheric parameters (A)</p> Signup and view all the answers

In what scenario would positioning be impossible using only two satellites?

<p>If the third dimension is not accounted for (D)</p> Signup and view all the answers

What is the orbital altitude at which satellites repeat their track over any point on Earth?

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

How many satellites are there in the described constellation?

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

Where is the Master Control facility for the Control Segment located?

<p>Schriever AFB, Colorado (B)</p> Signup and view all the answers

How many monitoring stations are part of the Control Segment?

<p>5 Monitoring Stations (C)</p> Signup and view all the answers

What do GPS receivers primarily compute using signals from satellites?

<p>Position, velocity, and time (C)</p> Signup and view all the answers

What is the typical error range when using GPS technology?

<p>3-10 meters (B)</p> Signup and view all the answers

How many satellites are required to compute the four dimensions of position and time?

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

What type of receivers are specifically made for individuals to carry?

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

Which statement accurately describes the funding and control of GPS?

<p>GPS is funded and controlled by the U.S. Department of Defense. (A)</p> Signup and view all the answers

What does GNSS stand for in relation to satellite navigation systems?

<p>Global Navigation Satellite System. (A)</p> Signup and view all the answers

What is the purpose of using four GPS satellite signals?

<p>To compute position in three dimensions and time offset. (D)</p> Signup and view all the answers

What is the role of the Space Segment in the GPS system?

<p>It is made up of the satellites that send radio signals. (D)</p> Signup and view all the answers

Who are the primary users of the GPS system?

<p>Civil users worldwide alongside military. (A)</p> Signup and view all the answers

What are the satellites in the GPS system also referred to as?

<p>Space vehicles. (B)</p> Signup and view all the answers

What is a primary characteristic of GPS signals?

<p>They provide specially coded radio range. (B)</p> Signup and view all the answers

What do GNSS systems include besides GPS?

<p>GLONASS from Russia, BeiDou from China, and Galileo from the EU. (C)</p> Signup and view all the answers

Flashcards

What is trilateration in GPS?

Trilateration is a method used by GPS to determine location. It involves calculating distances to multiple satellites and intersecting those distances to pinpoint your location.

How does GPS measure distance?

The distance between you and a satellite is determined by measuring the time it takes for a radio signal to travel from the satellite to your receiver.

How does the receiver calculate distance?

The receiver compares the radio signal's arrival time to its own internal clock to calculate the travel time, and thus the distance.

What is the speed of radio waves in GPS?

Radio waves, like those used by GPS, travel at the speed of light, approximately 186,000 miles per second.

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How do satellites communicate with receivers?

Each GPS satellite transmits a unique code that is synchronized with its internal clock. The receiver's internal clock compares this code to its own code to determine the time difference, and thus the distance.

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What is GPS?

Global Positioning System (GPS) is a satellite navigation system, originally designed for military use but now widely used for civilian purposes.

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What is the full name of the U.S. GPS system?

The Navstar system, also known as the NAVigation Satellite Timing And Ranging system, is the official name for the U.S. GPS system.

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Who controls and funds GPS?

GPS is funded and operated by the U.S. Department of Defense (DOD), although it's used globally by millions of civilians.

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What is GNSS?

Global Navigation Satellite Systems (GNSS) refers to a collection of satellite-based navigation systems from different countries, including GPS (USA), GLONASS (Russia), BeiDou (China), and Galileo (EU).

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How does GPS work?

GPS satellites transmit coded radio signals from space. These signals are received by GPS receivers on Earth, allowing them to calculate position, speed, and time.

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How many satellites are needed for GPS positioning?

A GPS receiver uses signals from at least four satellites to calculate its position in three dimensions (latitude, longitude, altitude) and the receiver's clock offset.

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GPS Satellite Orbit

The orbit altitude of 20,200 km, where satellites repeat their tracks over a specific point on Earth every 24 hours.

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GPS Constellation

The group of six planes in which GPS satellites orbit, equally spaced at 60 degrees apart, and inclined at 55 degrees to the equator.

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GPS Control Segment

The ground-based system responsible for controlling and managing GPS satellites, including tracking their orbits, sending them updates, and monitoring their health.

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Master Control Stations (MCS)

The Master Control Station (MCS) located at Schriever AFB in Colorado Springs and the backup MCS at Vandenberg AFB in California. These facilities are responsible for managing the entire GPS system.

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GPS Monitoring Stations

Four monitoring stations that track GPS satellites by receiving signals and incorporating that data into orbital models for each satellite.

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Satellite Ephemeris

Precise orbital data (ephemeris) for each satellite, containing information about its exact location in space and time.

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GPS User Segment

The part of the GPS system consisting of receivers that use satellite signals to determine position, velocity, and time.

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GPS Signal Processing

The process of converting satellite signals received by a GPS receiver into position, velocity, and time estimates.

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GPS Time Calculation

The difference in time between the GPS satellite's signal and the receiver's clock is used to calculate the distance to the satellite.

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GPS Synchronization

The signal from a GPS satellite contains a specific code that is known to both the satellite and the receiver. This code allows the receiver to synchronize its clock with the atomic clock on the satellite, improving accuracy.

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Fourth Satellite Principle

GPS receivers use a fourth satellite to eliminate errors in time calculations caused by differences in the time between the receiver and the satellites.

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Clock Error Compensation

When using three satellites to calculate position, any error in the receiver's clock will cause a shift in the calculated position. However, the timing error will be consistent across all satellite signals, allowing the receiver to compensate for the error.

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Accurate Clocks

By using a fourth satellite, the receiver can measure its clock error and adjust it to match the accurate atomic clocks on the satellites.

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Hidden Fourth Satellite

The fourth satellite in GPS is not directly visible but its signal is used in the background to calculate time and location accurately.

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Uses of GPS

GPS is used beyond navigation, providing precise measurements and corrections for various fields.

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Time and Frequency Dissemination

GPS technology is used to accurately measure time, making it valuable for various applications like research and telecommunications.

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Study Notes

Introduction to Global Positioning Systems

  • GPS, a satellite navigation system, is also known as the Navstar system (Navigation Satellite Timing And Ranging system).
  • The U.S. Department of Defense (DOD) funds and controls GPS.
  • Millions of people worldwide use GPS, but the system was originally designed for and is used by the U.S. military.
  • Other countries, such as the EU, Russia, and China, have their own global navigation satellite systems.

Presentation Outline

  • Definition and background of GPS
  • Components and segments of GPS
  • How GPS works
  • Time synchronization for atomic clock accuracy
  • Uses of GPS

Components and Segments of GPS

  • GPS consists of three segments: Space, Control, and User.

Space Segment

  • The Space Segment is made up of GPS satellites.
  • GPS satellites (also known as space vehicles, or SVs) send radio signals from space.
  • A GPS operational constellation has 24 satellites orbiting Earth.
  • Satellites orbit at 20,200 km.
  • Satellites are in six orbital planes with four satellites in each.
  • Orbital planes are equally spaced at 60-degree intervals.
  • They are inclined at 55° to the Earth's equatorial plane and retrace their path every 24 hours.
  • The satellites continuously pass over any point on Earth, providing users with signals from at least five to eight satellites, depending on their location.

Control Segment

  • The Control Segment tracks satellites using monitoring stations worldwide.
  • The Master Control Facility is at Schriever AFB, Colorado Springs.
  • There's an alternative facility at Vandenberg AFB in California.
  • Four other monitoring stations provide additional data for orbital models of each satellite.

User Segment

  • The User Segment includes GPS receivers used by users.
  • Receivers convert satellite signals into position, velocity, and time estimates.
  • Receivers generally require at least four satellites to compute three-dimensional (3D) position and time.
  • GPS receivers are used for navigation, positioning, time dissemination, and research purposes.
  • Receivers are designed for aircraft, ships, ground vehicles, and handheld use.

How GPS Works (Trilateration)

  • GPS uses trilateration to determine location.
  • Trilateration involves calculating distances from multiple satellites.
  • Measuring the time taken for signals to reach receivers from individual satellites allows computation of distances.
  • By knowing the distance, individuals can be located on a sphere around the satellite.

Measuring Distance (Pseudo-Range)

  • GPS calculates distance by timing radio signals.
  • Pseudo-range is the product of the speed of light and the travel time of the signal.
  • Radio waves travel at the speed of light (186,000 miles/second).
  • This method requires very accurate clocks to precisely measure travel times.

Synchronizing Clocks

  • Satellites have highly accurate atomic clocks.
  • Receivers have less precise clocks.
  • GPS uses a fourth satellite to adjust for differences between satellite and receiver clocks.
  • The receiver's clock is adjusted iteratively to get an accurate time measurement, which leads to an accurate position.

Uses of GPS

  • Precise position measurement at reference points
  • Surveying, geodetic control, and plate tectonic studies
  • Time and frequency dissemination
  • Astronomical observatories; Telecommunication facilities
  • Researching atmospheric parameters, landslides, and other Earth movement phenomena.
  • Search, rescue, and navigation

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Explore the fundamentals of Global Positioning Systems (GPS) in this quiz. Learn about its components, how it functions, and its applications in everyday life. Understand the significance of the satellite navigation system originally designed for the U.S. military and its global impact.

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