GIS Remote Sensing and Imagery 3 — Questions and Answers
Question 1: What is the primary advantage of hyperspectral imagery over multispectral imagery?
- Higher spatial resolution
- Hundreds of narrow contiguous spectral bands enabling material identification (Correct answer)
- Ability to penetrate cloud cover
- Faster revisit times
Correct answer: Hundreds of narrow contiguous spectral bands enabling material identification
Hyperspectral sensors capture hundreds of narrow bands, creating a detailed spectral signature that can identify specific minerals, vegetation species, or materials.
Question 2: Which phenomenon explains why satellite images acquired in the morning vs. afternoon may show different shadowing patterns?
- Atmospheric scattering variation
- Solar zenith angle change throughout the day (Correct answer)
- Earth's magnetic field influence
- Orbital precession effects
Correct answer: Solar zenith angle change throughout the day
The solar zenith angle changes throughout the day, altering shadow length and direction, which affects the appearance of terrain and objects in imagery.
Question 3: What does 'ground truth' mean in the context of remote sensing accuracy assessment?
- The elevation data used for orthorectification
- Field-collected reference data used to verify classification results (Correct answer)
- The raw uncorrected pixel values from the sensor
- GPS coordinates embedded in image metadata
Correct answer: Field-collected reference data used to verify classification results
Ground truth refers to field-verified observations of actual land cover used to train classifiers and validate classification accuracy.
Question 4: In a confusion matrix for land cover classification, what does the 'overall accuracy' metric represent?
- The percentage of pixels correctly classified across all classes (Correct answer)
- The accuracy of the most common land cover class only
- The ratio of false positives to true positives
- The Kappa coefficient adjusted for chance agreement
Correct answer: The percentage of pixels correctly classified across all classes
Overall accuracy is the total number of correctly classified pixels divided by the total number of pixels evaluated, expressed as a percentage.
Question 5: Which remote sensing technique is used to measure surface deformation caused by earthquakes or volcanic activity?
- LiDAR point cloud differencing
- InSAR (Interferometric SAR) (Correct answer)
- Thermal band analysis
- Panchromatic change detection
Correct answer: InSAR (Interferometric SAR)
InSAR compares phase differences between two SAR acquisitions to detect millimeter-scale ground deformation over large areas.
Question 6: What is the Landsat 8/9 band combination that best mimics natural color (true color) display?
- Bands 5-4-3 (NIR-Red-Green)
- Bands 4-3-2 (Red-Green-Blue) (Correct answer)
- Bands 6-5-4 (SWIR-NIR-Red)
- Bands 7-5-3 (SWIR-NIR-Green)
Correct answer: Bands 4-3-2 (Red-Green-Blue)
Bands 4 (Red), 3 (Green), and 2 (Blue) assigned to the RGB display channels produce a true-color composite that appears as the human eye would see the scene.
Question 7: Which factor most limits the use of optical remote sensing for tropical forest monitoring?
- Low spatial resolution of available sensors
- Persistent cloud cover blocking the surface (Correct answer)
- Lack of spectral bands for vegetation
- High cost of image acquisition
Correct answer: Persistent cloud cover blocking the surface
Tropical regions experience near-constant cloud cover, making it difficult to acquire cloud-free optical imagery, which is why SAR is often preferred for tropical monitoring.
GIS Remote Sensing and Imagery 3
What is the primary advantage of hyperspectral imagery over multispectral imagery?