GIS Geospatial Data Acquisition 2 — Questions and Answers
Question 1: Which satellite constellation is the European equivalent of GPS, providing global navigation services?
- GLONASS
- Galileo (Correct answer)
- BeiDou
- IRNSS
Correct answer: Galileo
Galileo is the European Union's global navigation satellite system, providing high-accuracy positioning services independent of GPS.
Question 2: In LiDAR data acquisition, what does 'point density' refer to?
- The weight of the LiDAR sensor
- The number of laser pulses emitted per second
- The number of points per unit area on the ground (Correct answer)
- The intensity of the laser return signal
Correct answer: The number of points per unit area on the ground
Point density in LiDAR refers to the number of measured points per square meter or square foot on the ground surface.
Question 3: What is 'dead reckoning' in the context of GPS navigation?
- Estimating position using known speed, direction, and elapsed time when GPS signal is lost (Correct answer)
- Calculating the exact GPS satellite positions
- Removing multipath errors from GPS data
- Averaging multiple GPS readings for accuracy
Correct answer: Estimating position using known speed, direction, and elapsed time when GPS signal is lost
Dead reckoning estimates current position by using a previously known position and advancing it using speed, heading, and time when GPS signals are unavailable.
Question 4: What type of remote sensing uses radar pulses to detect surface elevation and penetrate vegetation?
- Multispectral imaging
- Synthetic Aperture Radar (SAR) (Correct answer)
- Thermal infrared sensing
- Hyperspectral imaging
Correct answer: Synthetic Aperture Radar (SAR)
SAR uses microwave radar pulses that can penetrate cloud cover and vegetation canopy, making it useful for mapping terrain beneath forest cover.
Question 5: What is the primary purpose of ground control points (GCPs) in aerial photogrammetry?
- To calibrate the camera lens distortion
- To georeference and improve the accuracy of aerial imagery (Correct answer)
- To determine the flight altitude of the aircraft
- To measure atmospheric refraction
Correct answer: To georeference and improve the accuracy of aerial imagery
GCPs are surveyed points on the ground with known coordinates used to georeference aerial photos and correct positional errors in photogrammetric products.
Question 6: Which data acquisition method is most appropriate for mapping underwater seafloor topography?
- Aerial LiDAR
- Multibeam echo sounder (MBES) (Correct answer)
- Terrestrial laser scanning
- Photogrammetry from satellites
Correct answer: Multibeam echo sounder (MBES)
Multibeam echo sounders emit acoustic pulses in a fan pattern and measure the time for returns, creating detailed seafloor bathymetric maps.
Question 7: What is 'scan angle' (or field of view) in airborne LiDAR systems?
- The angle at which the laser pulses hit the ground
- The angular range the scanner sweeps side-to-side from nadir (Correct answer)
- The vertical angle of the aircraft during flight
- The angle between two overlapping flight lines
Correct answer: The angular range the scanner sweeps side-to-side from nadir
The scan angle defines the maximum angular deviation from nadir (directly below) that the LiDAR scanner sweeps, determining the width of the data swath collected.
GIS Geospatial Data Acquisition 2
Which satellite constellation is the European equivalent of GPS, providing global navigation services?