Geodetic Data and Positioning Systems
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Questions and Answers

What is the main purpose of GNSS?

The main purpose of GNSS is to determine location anywhere on Earth using satellite signals.

How many satellites are required for 3D positioning?

At least 4 satellites are required for 3D positioning.

What are the three main segments of a GPS system?

The three main segments of a GPS system are the space segment, control segment, and user segment.

Why are atomic clocks used in satellites?

<p>Atomic clocks are used in satellites to measure time extremely accurately, essential for precise positioning.</p> Signup and view all the answers

What is the significance of the World Geodetic System 96 (WGS96)?

<p>WGS96 provides a standard for referencing elevation and geodetic data in positioning calculations.</p> Signup and view all the answers

Name one example of a Global Navigation Satellite System.

<p>One example of a GNSS is NavStar GPS from the USA.</p> Signup and view all the answers

What role do tracking stations play in the GPS system?

<p>Tracking stations monitor satellite positions and calculate orbital data relative to WGS84.</p> Signup and view all the answers

How do GNSS receivers determine their location?

<p>GNSS receivers calculate their location based on the time signals take to travel from multiple satellites.</p> Signup and view all the answers

What role does chlorophyll play in the spectral reflectance of plants?

<p>Chlorophyll reflects and absorbs light at different wavelengths, mainly reflecting green light, which is why healthy plants appear green.</p> Signup and view all the answers

How do multispectral sensor systems differ from panchromatic sensor systems?

<p>Multispectral sensor systems can detect more than three different levels of energy, while panchromatic systems typically shift between black and white with a single detector.</p> Signup and view all the answers

What is spectral reflectance and why is it important in remote sensing?

<p>Spectral reflectance measures how much light an object reflects at different wavelengths, essential for identifying materials and monitoring environmental conditions.</p> Signup and view all the answers

Describe the process and importance of orthophoto correction.

<p>Orthophoto correction removes distortions from aerial images to create a uniform scale, allowing them to be used accurately like maps.</p> Signup and view all the answers

What are active sensors, and how do they function in remote sensing?

<p>Active sensors emit their own energy, like radar or LIDAR, to measure properties such as forest density by analyzing the feedback from their emitted signals.</p> Signup and view all the answers

Explain the concept of ground truthing in the context of remote sensing.

<p>Ground truthing involves validating remote sensing data by comparing it with actual observations or measurements taken on the ground.</p> Signup and view all the answers

How can radar sensors contribute to environmental monitoring?

<p>Radar sensors can analyze forest density and create 3D images of tree cover by measuring the feedback from emitted radar waves.</p> Signup and view all the answers

What does the term 'fisheye distortion' refer to in remote sensing?

<p>Fisheye distortion is the warping of images caused by the angle of the sensor, particularly when capturing imagery from above.</p> Signup and view all the answers

Why is higher resolution not always preferable in remote sensing?

<p>Higher resolution might not be beneficial if it leads to unnecessary data complexity or if it requires impractical sensor altitudes.</p> Signup and view all the answers

What is the rectification process in remote sensing?

<p>Rectification involves converting raster data into vector format and aligning it with different geographic datums for accurate representation.</p> Signup and view all the answers

What is the primary use of absolute GPS and what is its average error?

<p>Absolute GPS is used in navigation systems and has an average error of 5-10 meters.</p> Signup and view all the answers

How does statistical GPS reduce positioning error, and what is its average error?

<p>Statistical GPS requires staying in one position to log the signal and has an average error of 0.5 to 2 cm.</p> Signup and view all the answers

What additional technology does Differential GPS use to improve precision?

<p>Differential GPS utilizes a reference station with a known position to calculate corrections for the satellites' signals.</p> Signup and view all the answers

Describe the role of SWEPOS in differential GPS.

<p>SWEPOS serves as a national grid of reference stations that provides corrections for differential GPS.</p> Signup and view all the answers

What is the relationship between single-station RTK and network RTK methods?

<p>Single-station RTK uses one reference station while network RTK uses multiple stations to reduce positional error.</p> Signup and view all the answers

What factors can affect GPS positioning precision?

<p>Atmospheric disturbances and environmental factors like solar storms can affect GPS precision.</p> Signup and view all the answers

How do real-time kinematics (RTK) improve positioning accuracy?

<p>RTK provides real-time corrections from a nearby base station to enhance positional accuracy to 0.5 - 5 cm.</p> Signup and view all the answers

What distinguishes satellite-based augmentation systems (SBAS) from land-based systems?

<p>SBAS uses reference stations on satellites for correction, while land-based systems rely on ground stations.</p> Signup and view all the answers

Explain the concept of infield GIS.

<p>Infield GIS combines GPS with GIS software on portable devices for real-time data collection in the field.</p> Signup and view all the answers

What is the average precision of network RTK in high-density traffic areas?

<p>Network RTK can achieve positional precision in real-time measurements at the millimeter level.</p> Signup and view all the answers

In remote sensing, what is the primary source of energy measured by sensors?

<p>The primary source of energy is sunlight emitted by the sun that interacts with the Earth's surface.</p> Signup and view all the answers

How do satellite positions relate to the WGS84 reference system?

<p>Satellite positions are based on the WGS84 reference system, which defines the location of points on the Earth's surface.</p> Signup and view all the answers

What impact does ionic activity have on GPS positioning accuracy?

<p>Ionic activity can create disturbances that lead to errors in the signals received from satellites.</p> Signup and view all the answers

What is the significance of using multiple reference stations in network RTK?

<p>Multiple reference stations enable spatially varying compensation for atmospheric sources of positional error.</p> Signup and view all the answers

What are the two main categories of infield GIS devices mentioned?

<p>The two categories are devices using ArcPad and those specifically designed for handheld use with ArcGIS.</p> Signup and view all the answers

What role does chlorophyll play in remote sensing?

<p>Chlorophyll absorbs specific wavelengths of light, which can be measured to gather information about vegetation health.</p> Signup and view all the answers

Study Notes

Geodetic Data and Positioning Systems

  • Primary geographic data requires a positioning system and sensor for attribute capture.
  • Global Navigation Satellite Systems (GNSS) use satellites to determine location.
  • GNSS satellites orbit Earth and send signals to receivers.
  • Receivers calculate location based on signal travel time from multiple satellites.
  • At least four satellites are needed for 3D positioning (latitude, longitude, altitude), three for 2D.
  • Elevation is relative to the World Geodetic System 1984 (WGS84).
  • Examples of GNSS: GPS (USA), GLONASS (Russia), Galileo (EU), BeiDou (China)
  • GNSS Advantages: Global coverage, 24/7 operation, high accuracy.
  • Satellite Systems include the Space segment (satellites in precise orbit relative to WGS84), Control segment (tracking stations, operating data), and User segment (receivers & users).
  • Minimum of 24 satellites are kept in 6 orbital planes, positioned 55 degrees to the equator, with higher density at the equator.
  • Satellites have atomic clocks for precise timekeeping.
  • Amplitude Modulation (AM) is used for satellite signal transmission.
  • Bearings from satellites allow location calculation (like lighthouse bearings).
  • Location accuracy depends on the number of satellite positions available.

GPS Positioning Techniques

  • Absolute GPS: Real-time positioning, average error 5-10m (constant error), suitable for navigation.
  • Statistical GPS: Requires stationary position for detailed atmospheric error calculation. Uses absolute GPS data, accuracy 0.5-2cm.
  • Differential GPS: Uses a known reference station to correct for atmospheric distortion. Increases accuracy, average error 1-2m, uses AM and FM signals, allows for real-time correction of satellite signals.
  • SWEPOS: National Swedish reference station network for differential GPS. Accuracy depends on proximity to reference stations.
  • Single-Station RTK (Real-Time Kinematics): Uses a base station for real-time error correction, average precision 0.5-5cm, susceptible to atmospheric conditions and solar activity.
  • Network RTK (Real-Time Kinematics): Uses multiple reference stations for improved accuracy, mm precision in high traffic areas. Differential GPS used in lower traffic densities.

Satellite Based Augmentation Systems (SBAS)

  • Satellite-based reference stations above long-haul aircraft provide positioning data in areas far from land-based augmentation systems.

Land Based Augmentation Systems

  • Land-based reference stations provide position data corrections in the atmosphere.

Reference Frames

  • Global: WGS84
  • National: RT90
  • Local: RT90 (0 gon)

Geographic Information Systems (GIS)

  • Infield GIS combines GPS and GIS software for field data collection.
  • Includes handheld devices like ArcPad.

Remote Sensing

  • Remote sensing captures attribute data via sensors on various platforms (satellites, aircraft, drones).
  • Sunlight is a primary energy source.
  • Sensors measure reflected/resonated energy from Earth's surface.
  • Different materials reflect sunlight differently, forming spectral "fingerprints".
  • Spectral Resolution:
    • Panchromatic: Black and white, single detector.
    • Multispectral: Multiple energy levels.
    • Hyperspectral: Multiple simultaneous energy levels.
  • Spectral reflectance is how much light an object reflects at different wavelengths.
  • Chlorophyll shows a distinct wavelength dip in spectral reflectance.
  • Ground Truthing: Provides accurate spatial attributes to remote sensing data.
  • Higher sensor resolution is not always beneficial, it varies with different altitudes.

Photogrammetry & Ortho-Rectification

  • Orthophotos: Remove distortions (fish-eye, terrain). Ensures all items in the photo are seen from above and are seen perpendicular to the center of the photo.
  • Active Sensors: Emit their own energy (radar, lidar)

Example: Chlorophyll Spectral Reflectance

  • Chlorophyll reflects and absorbs different light wavelengths.
  • Reflectance patterns help identify plant health and type.

Data Rectification

  • Raster-to-vector/vector-to-raster conversion, e.g. updating historical maps.

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Description

This quiz delves into the fundamentals of geodetic data and the various positioning systems such as Global Navigation Satellite Systems (GNSS). Discover how satellites like GPS and Galileo aid in accurately determining geographical locations. Test your understanding of satellite classification, operating segments, and the advantages these systems offer.

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