GIS Remote Sensing and Imagery 5 — Questions and Answers
Question 1: Which accuracy assessment metric accounts for the possibility of chance agreement between classified and reference data?
- Overall accuracy
- Producer's accuracy
- User's accuracy
- Kappa coefficient (Correct answer)
Correct answer: Kappa coefficient
The Kappa coefficient (κ) adjusts overall accuracy for the agreement that could occur by chance, providing a more rigorous measure of classification quality.
Question 2: In object-based image analysis (OBIA), what is the first step before classification?
- Applying atmospheric correction
- Image segmentation to create homogeneous objects (Correct answer)
- Calculating spectral indices
- Performing principal component analysis
Correct answer: Image segmentation to create homogeneous objects
OBIA begins with image segmentation, which groups adjacent pixels with similar spectral, spatial, and textural properties into discrete objects before classification.
Question 3: What is the main advantage of using a sun-synchronous orbit for Earth observation satellites?
- The satellite can image any location on Earth at any time
- The satellite passes over any given location at the same local solar time, ensuring consistent illumination (Correct answer)
- The satellite remains stationary over one area for continuous monitoring
- The satellite achieves the highest possible spatial resolution
Correct answer: The satellite passes over any given location at the same local solar time, ensuring consistent illumination
Sun-synchronous orbits are designed so the satellite crosses the equator at the same local solar time on every pass, minimizing illumination variation between acquisitions.
Question 4: What does the term 'orthorectification' correct for in aerial and satellite imagery?
- Atmospheric haze and scattering effects
- Displacement of features caused by terrain relief and sensor geometry (Correct answer)
- Color balance differences between image strips
- Radiometric inconsistencies between adjacent detectors
Correct answer: Displacement of features caused by terrain relief and sensor geometry
Orthorectification uses a digital elevation model (DEM) and sensor model to remove relief displacement and produce a planimetrically accurate image where every pixel is in its true geographic position.
Question 5: Which remote sensing platform is best suited for rapid disaster response mapping due to its cloud-penetrating capability and day/night operation?
- High-resolution optical satellites like WorldView-3
- Synthetic Aperture Radar (SAR) satellites like Sentinel-1 (Correct answer)
- MODIS aboard Terra/Aqua
- Airborne hyperspectral scanners
Correct answer: Synthetic Aperture Radar (SAR) satellites like Sentinel-1
SAR systems operate regardless of cloud cover or sunlight, making them ideal for post-disaster mapping when optical imagery is often blocked by storm clouds.
Question 6: In the electromagnetic spectrum, which region is used by LiDAR systems for topographic mapping?
- Microwave (1 cm–1 m)
- Near-infrared to visible light (532–1064 nm laser pulses) (Correct answer)
- Thermal infrared (8–14 µm)
- Shortwave infrared (1.5–2.5 µm)
Correct answer: Near-infrared to visible light (532–1064 nm laser pulses)
LiDAR systems typically use near-infrared (1064 nm) or green (532 nm) laser pulses that reflect off surfaces and return to the sensor for distance measurement.
Question 7: What is 'temporal resolution' in the context of satellite remote sensing?
- The smallest object that can be detected in an image
- The number of spectral bands available on the sensor
- The frequency with which a satellite revisits and images the same location (Correct answer)
- The precision of radiometric measurement in bit depth
Correct answer: The frequency with which a satellite revisits and images the same location
Temporal resolution refers to the revisit time or repeat cycle of a satellite — how frequently it can acquire a new image of the same location on Earth.
GIS Remote Sensing and Imagery 5
Which accuracy assessment metric accounts for the possibility of chance agreement between classified and reference data?