GIS Geospatial Data Acquisition 4 — Questions and Answers
Question 1: What is 'geometric resolution' in the context of satellite imagery?
- The number of spectral bands captured by the sensor
- The smallest ground feature that can be detected, typically expressed as meters per pixel (Correct answer)
- The frequency at which a satellite revisits the same location
- The accuracy of the satellite's internal clock
Correct answer: The smallest ground feature that can be detected, typically expressed as meters per pixel
Geometric (spatial) resolution defines the minimum size of a feature distinguishable on an image, with smaller values (e.g., 0.3m) indicating finer detail than larger values (e.g., 30m).
Question 2: What is the purpose of a 'calibration target' used during aerial or satellite image acquisition?
- To mark the corners of the study area
- To provide known reflectance values for converting digital numbers to physical radiance or reflectance (Correct answer)
- To track the flight path of the aircraft
- To synchronize the camera shutter with GPS timestamps
Correct answer: To provide known reflectance values for converting digital numbers to physical radiance or reflectance
Calibration targets have precisely known spectral reflectance properties, enabling radiometric calibration that converts raw sensor values to standardized, physically meaningful reflectance values.
Question 3: What is 'strip adjustment' in the context of airborne LiDAR processing?
- Trimming data at the edges of each flight strip
- Aligning overlapping flight strips to minimize positional inconsistencies between them (Correct answer)
- Adjusting point density across different flight altitudes
- Filtering ground returns from vegetation returns
Correct answer: Aligning overlapping flight strips to minimize positional inconsistencies between them
Strip adjustment compares overlapping regions of adjacent flight lines and applies corrections to minimize offsets caused by IMU/GPS errors, ensuring consistent elevation values across the entire survey.
Question 4: Which of the following best describes 'crowdsourced geospatial data' (VGI)?
- Data collected by government surveyors using certified instruments
- Geographic information contributed by the public, often via smartphones or web platforms (Correct answer)
- Satellite imagery purchased from commercial providers
- Automated data collection from IoT sensor networks
Correct answer: Geographic information contributed by the public, often via smartphones or web platforms
Volunteered Geographic Information (VGI) is geospatial data gathered from citizen contributors, exemplified by projects like OpenStreetMap where users map roads, buildings, and features.
Question 5: In photogrammetry, what is the 'base-to-height ratio' and why does it matter?
- The ratio of camera focal length to flying height, which determines image scale
- The ratio of the distance between camera positions (base) to flying height, affecting vertical accuracy of stereo models (Correct answer)
- The ratio of forward overlap to side overlap in a flight plan
- The ratio of ground sample distance to image pixel size
Correct answer: The ratio of the distance between camera positions (base) to flying height, affecting vertical accuracy of stereo models
The base-to-height ratio (B/H) describes the geometry of stereo image pairs; larger ratios provide better vertical accuracy for elevation models but can cause matching difficulties.
Question 6: What is 'atmospheric correction' in remote sensing?
- Correcting satellite imagery for geometric distortions caused by Earth's curvature
- Removing or compensating for the effects of atmospheric scattering and absorption on sensor-recorded radiance (Correct answer)
- Adjusting image brightness for different sun angles
- Filtering out radar interference from weather systems
Correct answer: Removing or compensating for the effects of atmospheric scattering and absorption on sensor-recorded radiance
Atmospheric correction converts sensor-measured top-of-atmosphere radiance to surface reflectance by modeling and removing the contributions of atmospheric scattering and absorption.
Question 7: A GIS project requires mapping vegetation across 10,000 square kilometers quickly and cost-effectively. Which data acquisition method is most appropriate?
- Terrestrial laser scanning (TLS)
- Satellite multispectral imagery (Correct answer)
- Total station field survey
- UAV photogrammetry
Correct answer: Satellite multispectral imagery
Satellite multispectral imagery is ideal for large-area mapping because a single satellite pass can cover thousands of square kilometers, making it far more cost-effective than ground-based or UAV methods at this scale.
GIS Geospatial Data Acquisition 4
What is 'geometric resolution' in the context of satellite imagery?