GNSS Positioning and Applications Quiz
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Questions and Answers

What is a key advantage of static methods in positioning?

  • Speed in data collection
  • Cost-effectiveness compared to topographic methods (correct)
  • Lower precision compared to dynamic methods
  • Requiring continuous movement for accuracy

Which application is NOT typically associated with static positioning?

  • Tectonic Movement Monitoring
  • Deformation monitoring in dams and structures
  • Geodetic Control
  • Kinematic Positioning of moving objects (correct)

For a baseline length of 50-100 km, what is the minimum observation time required?

  • Minimum 3 hours
  • Minimum 2 hours (correct)
  • 2 hours
  • 1 hour

What happens if ambiguity is lost in kinematic positioning?

<p>The process must be re-initialized. (D)</p> Signup and view all the answers

What is essential for sustaining accuracy in kinematic positioning?

<p>Continuous ambiguity maintenance (C)</p> Signup and view all the answers

What is the primary focus area of the geostationary orbit (GEO) satellite described?

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

How many satellites comprise the IRNSS/NAVIC system?

<p>7 (A)</p> Signup and view all the answers

Which GNSS system has the highest number of operational satellites listed?

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

What type of orbit do the four inclined GEO satellites of the IRNSS follow?

<p>Figure-eight orbit (C)</p> Signup and view all the answers

Which of the following is primarily a Kinematic-RTK application?

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

Which of the following is NOT a source of error in GNSS accuracy?

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

What error arises when satellite clocks drift from the GNSS system's time?

<p>Satellite clock error (D)</p> Signup and view all the answers

What is one of the main uses of GNSS methods?

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

How many orbital planes are used by the NAVSTAR-GPS satellites?

<p>6 (B)</p> Signup and view all the answers

In which atmospheric layer is signal refraction more pronounced?

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

How many frequencies does the IRNSS/NAVIC system use according to the operational status?

<p>1 (B)</p> Signup and view all the answers

Which GNSS system is particularly effective in polar regions?

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

What is the orbital altitude of the GALILEO satellites?

<p>23,222 km (A)</p> Signup and view all the answers

How many satellites does the BEIDOU navigation system consist of?

<p>35 (A)</p> Signup and view all the answers

Which of the following GNSS applications is specifically mentioned under GNSS applications?

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

What is the inclination angle of satellites in the GLONASS system?

<p>64.8° (D)</p> Signup and view all the answers

What is the primary effect of multipath on GNSS signals?

<p>It causes signal distortion and degrades navigation accuracy. (A)</p> Signup and view all the answers

Which factors can influence the accuracy of ephemeris data?

<p>Gravity, solar radiation pressure, and atmospheric drag. (B)</p> Signup and view all the answers

How does GDOP affect positioning accuracy?

<p>GDOP quantifies the geometric strength of satellite coverage. (A)</p> Signup and view all the answers

What is the purpose of Differential Positioning?

<p>To enhance accuracy by using a fixed reference station. (C)</p> Signup and view all the answers

Which method is primarily used to enhance GNSS positioning accuracy through signal corrections from geostationary satellites?

<p>Satellite-Based Augmentation Systems (SBAS) (B)</p> Signup and view all the answers

What does horizontal dilution of precision (HDOP) specifically impact?

<p>Horizontal positioning accuracy. (A)</p> Signup and view all the answers

How does space weather, particularly solar activity, affect GNSS signals?

<p>It decreases the density of the ionosphere, leading to increased refraction errors. (C)</p> Signup and view all the answers

What does improper antenna mounting primarily lead to?

<p>Significant positioning errors. (A)</p> Signup and view all the answers

What is the primary purpose of the Global Navigation Satellite System (GNSS)?

<p>To offer precise positioning and synchronization information globally (C)</p> Signup and view all the answers

How many satellites must a receiver communicate with to accurately determine its three-dimensional position?

<p>At least three satellites (D)</p> Signup and view all the answers

What is the altitude range for Medium Earth Orbit (MEO) satellites?

<p>From 19,180 to 28,000 km (B)</p> Signup and view all the answers

Which segment of GNSS is responsible for controlling and monitoring the satellites?

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

What is essential for the accuracy of GNSS measurements?

<p>The signal travel time from satellites (B)</p> Signup and view all the answers

How many satellites are required for three-dimensional positioning?

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

Why do GNSS satellites need to be distributed in different orbital planes?

<p>To ensure visibility from any location on Earth (C)</p> Signup and view all the answers

Which method relies on analyzing frequency shifts to determine distance?

<p>The Doppler Effect (C)</p> Signup and view all the answers

What is the primary use of Low Earth Orbit (LEO) satellites?

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

What mechanism do communication satellites utilize within the GNSS framework?

<p>They enhance GNSS by retransmitting corrected information (D)</p> Signup and view all the answers

Which of the following accurately describes the function of the satellite's almanac?

<p>Valid for about 6 months (B)</p> Signup and view all the answers

What function do spare satellites serve in the GNSS system?

<p>They ensure global coverage and allow for speedy replacements (A)</p> Signup and view all the answers

What frequency does the L2 carrier wave transmit at?

<p>1227.60 MHz (B)</p> Signup and view all the answers

When was the Global Positioning System (NAVSTAR - GPS) originally developed?

<p>During the 1970s (A)</p> Signup and view all the answers

How is distance calculated using Code Measurement?

<p>By measuring full and fractional wavelengths of the signal (B)</p> Signup and view all the answers

Which code modulates the L1 carrier at a frequency of 1.023 MHz?

<p>C/A code (D)</p> Signup and view all the answers

Flashcards

GNSS

Global Navigation Satellite System, a constellation of orbiting satellites used to determine precise positions on Earth.

Spatial Segment (GNSS)

The part of a GNSS system consisting of the satellites that transmit navigation signals.

Satellite Position

The precise location of a satellite in space, used to calculate distances.

Ephemeris

Satellite data transmitted by a GNSS satellite, including its current position, used for calculations.

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Distance Calculation (GNSS)

Determining the distance between a receiver and a satellite, crucial to calculate 3D position.

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Control Segment (GNSS)

The part of a GNSS system responsible for monitoring and controlling satellites.

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User Segment (GNSS)

The part of a GNSS system that includes the receivers used by users on Earth to receive and process signals.

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Global Coverage (GNSS)

Ensuring signals from the GNSS satellites are available to receivers anywhere on Earth.

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Satellite Orbit Types

Satellites can orbit Earth at different altitudes, categorized as Low Earth Orbit (LEO) or Mean Earth Orbit (MEO).

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Satellite Positioning - Almanac

A set of orbital parameters used for approximating a satellite's position, generally valid for a few months.

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Satellite Positioning - Ephemeris

Precise data on a satellite's position, updated regularly.

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Satellite Positioning - Measuring Distance

The process of calculating the distance between a satellite and a receiver using signal travel time, important for determining precise locations.

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Three-Dimensional Positioning

Determining a location's position in three-dimensional space, requiring signals from at least three satellites.

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Satellite L-Band Carrier Waves

Radio waves used by satellites for transmitting data; these waves are found at particular frequencies.

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Satellite Code Modulation

Carrier waves in GPS are modulated with codes to transmit data on their positions.

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Doppler Effect in GPS

A process that aids in calculating the distance between a receiver and a satellite by examining the changes in signals' frequencies (Doppler shift).

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Static Positioning

A positioning technique where a receiver stays at a fixed point for an extended time to achieve high precision measurements.

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Static Positioning Applications

Static positioning is used in various applications, including establishing geodetic control points, monitoring tectonic movements, and precisely measuring structures.

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Static Rapid Positioning

A static positioning method that reduces observation time and baseline lengths, enabling faster location determination.

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Kinematic Positioning

A positioning technique designed for tracking moving objects, requiring continuous ambiguity resolution and a reference station.

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Kinematic-RTK

A differential positioning method employing a stationary reference station and a moving rover, enhancing accuracy by mitigating specific GNSS errors.

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Kinematic RTK Applications

These applications use real-time kinematic (RTK) technology combined with precise positioning data from Global Navigation Satellite Systems (GNSS) to determine extremely accurate positions of moving objects or for highly detailed surveys.

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Trajectory Determination

Using RTK, this application enables tracking the path of moving objects with high accuracy over time, creating a precise record of their movements.

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Precise Positioning of Moving Objects

RTK can provide incredibly accurate real-time position data for moving objects like vehicles, ships, or even drones, essential for applications like autonomous navigation.

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Detailed Surveying

RTK-enabled surveys produce highly detailed and accurate measurements for construction projects, providing crucial information for planning and execution.

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Hydrographic Surveys

These surveys use RTK to map the underwater landscape, providing detailed information about water depths, bathymetry, and shoreline features.

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Bathymetric Surveys

Similar to hydrographic surveys, these focus on mapping the underwater terrain, creating detailed charts and models of seabed topography for various purposes.

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GNSS Constellations

Different countries and organizations operate their own networks of satellites, known as constellations, providing global coverage for position determination.

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NAVSTAR-GPS

The United States' global navigation satellite system, consisting of 31 satellites in orbit around Earth, providing accurate location data worldwide.

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What is NAVIC IRNSS?

A regional navigation system operated by India, consisting of a constellation of 7 satellites, including 3 GEO and 4 Inclined GEO satellites.

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What are the different types of GNSS constellations?

There are several GNSS constellations like GPS (USA), GLONASS (Russia), BEIDOU (China), GALILEO (EU), QZSS (Japan), and IRNSS/NAVIC (India).

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What is the difference between GEO and IGSO satellites?

GEO (Geostationary Earth Orbit) satellites remain at a fixed point above Earth, whereas IGSO (Inclined Geosynchronous Orbit) satellites follow a figure-eight pattern, crossing the equator at specific longitudes.

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What are the main sources of error in GNSS?

GNSS accuracy can be affected by factors like satellite and receiver clock errors, atmospheric refraction, multipath effects, and other environmental factors.

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How are satellite clock errors mitigated?

Satellite clock errors are minimized by continuous corrections provided by the GNSS system's control segment.

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How does atmospheric refraction affect GNSS?

Signal paths through the atmosphere are bent due to variations in density, affecting signal travel time and distance calculations. This is more pronounced at lower frequencies.

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How are atmospheric refraction errors mitigated?

GNSS systems use multi-frequency measurements to estimate and correct for atmospheric delays.

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Why is GNSS accuracy important?

Precise GNSS readings are crucial for various applications like topography, geodesy, and geomatics, where accurate location information is essential.

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Multipath

When signals bounce off multiple surfaces, reaching the receiver at different times with different strengths. This distorts the signal, degrading navigation accuracy.

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Ephemeris Errors

Ephemeris data predict a satellite's position, but real-world factors like gravity and solar radiation affect its actual orbit. This difference can lead to positioning errors.

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Improper Antenna Mounting

Incorrectly placing the antenna during installation can significantly impact positioning accuracy. Ensure it's level and centered over the reference point.

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Geometric Dilution of Precision (GDOP)

Quantifies the strength of satellite coverage. It indicates the uncertainty of the receiver's position based on satellite positions relative to it. Higher GDOP means greater uncertainty.

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Horizontal Dilution of Precision (HDOP)

A type of GDOP that affects the accuracy of horizontal positioning.

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Vertical Dilution of Precision (VDOP)

A type of GDOP that influences the accuracy of vertical positioning.

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Space Weather

Solar activity, particularly flares, can affect the ionosphere's density, impacting GNSS signals and causing refraction errors. Accuracy decreases during periods of high activity.

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Differential Positioning

Two or more receivers, one fixed (reference) and the other moving. The fixed receiver sends corrections to the moving one, improving accuracy.

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Study Notes

GNSS Systems (Global Navigation Satellite Systems)

  • GNSS emerged in the 1970s with the development of the NAVSTAR-GPS (US military application).
  • Civil use extended in the 1990s.
  • GNSS provide precise positioning and timing anywhere on Earth, economically.
  • They don't require visual line-of-sight between stations.
  • GNSS systems are constellations of satellites orbiting the Earth at various altitudes.
  • Signals from these satellites enable the calculation of a receptor's 3D position on earth.
    • Calculating 3D position involves measuring distance to at least three known satellite positions.
    • A fourth satellite is needed to calculate altitude.
  • Satellite's ephemeris are used to measure the distance between the receiver and satellites using signal travel time.
  • Accurate satellite clocks (timekeeping) are important for precise distance measurements.
  • GNSS systems are split into Space, Control, and User segments.

Space Segment

  • Contains the navigation satellites.
  • Transmit signals on different frequencies.
  • Includes a constellation of satellites for communication and navigation.
  • A sufficient number of satellites are required to ensure global coverage.
  • Backup satellites are available to replace components or for additional coverage.
  • Satellites need to be distributed in multiple orbital planes.
  • A minimum of five visible satellites should always be present over any location.

Control Segment

  • Monitors satellites' signals and orbital parameters.
  • Tracks the positions of satellites over time.
  • Transmits this information to a central station (CSOC, Colorado Springs, USA).
  • Uses the data to predict satellite orbits and clock corrections.
  • Uploads information about orbits and clock corrections to the satellites so receivers can use it to determine position.
    • Monitors satellite health and subsystems (solar panels, energy from batteries, propellers).
  • Updates navigation messages with ephemeris, almanac, and clock corrections to satellites.
  • Solves any issues with individual satellites.
    • Manages the availability and anti-spoofing of the signals.
    • Tracks each satellite's status passively.

User Segment

  • Consists of GPS/GNSS receivers.
  • Includes military receivers, mobile phones, and vehicles.
  • Captures satellite signals and determines location, speed, or time.
  • Different types of receptors are possible (passive or active).

Support Segment

  • Consists of ground stations.
  • Collect data on satellites' positions.
  • Corrects position inaccuracies.
  • Forms part of both the control and user segments.

Geostationary Earth Orbit (GEO) Satellites

  • Orbit the Earth at about 35,848 km.
  • Appear stationary from a ground-based perspective. They orbit at a speed identical to the Earth's rotation, so their position relative to the Earth remains constant.
  • Used in communication and some augmentation systems (SBAS).

Medium Earth Orbit (ΜΕΟ) Satellites

  • Orbit at altitudes between 19,180 and 28,000 km.
  • Used in positioning systems.

Low Earth Orbit (LEO) Satellites

  • Orbit at roughly 800 km.
  • Primarily used for observation.

Calculation of Position

  • Satellites' positions and clock data are necessary.
  • Receivers measure signals’ travel times.
  • Calculating distances from the receiver to several satellites yields the receiver’s position and time.

Signal Characteristics

  • Satellites constantly transmit on two carrier waves (L1 and L2).
  • Wave frequencies are based on precisely timed atomic clocks.
  • Each carrier wave is modulated by two codes: C/A and P-code.
    • C/A code is for general use, offering lower precision.
    • P-code is for secure applications, delivering higher precision.

Errors in GNSS

  • Errors come from both systematic and random sources.
  • Satellite clocks and receiver clocks introduce errors.
  • Ionospheric and tropospheric delays cause further inaccuracies.

GNSS Constellations Overview

  • GPS: US-based, 24 satellites in six planes.
  • GLONASS: Russian, 24 satellites in three planes.
  • BeiDou: Chinese, 35 satellites in 3+ orbits.
  • QZSS: Japanese, primarily for the Asian region and has three GEO satellites and one in geosynchronous orbit
  • Galileo: European, 26 satellites in three planes.
  • IRNSS/NAVIC: Indian Regional Navigational Satellite System, four in geosynchronous orbit plus three in medium earth orbit

Methods of Observation

  • Static
  • Rapid Static
  • Kinematic
  • Real-time Kinematic (RTK)

Types of Applications

  • Control Surveys
  • Topographic Surveys
  • Replanning
  • GIS-based applications
  • Navigation
  • Tracking

Additional Notes

  • Different GNSS systems have various orbital characteristics.
  • GNSS technologies are constantly evolving for higher accuracy and availability.

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GNSS Systems Introduction PDF

Description

Test your knowledge on GNSS positioning methods, their applications, and the technical details of various satellite systems. This quiz covers static and kinematic positioning, errors in GNSS accuracy, and the operational satellites within the IRNSS/NAVIC and NAVSTAR-GPS systems.

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