GIS Remote Sensing and Imagery 2 — Questions and Answers
Question 1: Which type of satellite orbit provides continuous coverage of the same area on Earth's surface?
- Geostationary orbit (Correct answer)
- Sun-synchronous orbit
- Polar orbit
- Low Earth orbit
Correct answer: Geostationary orbit
Geostationary satellites orbit at ~35,786 km and remain fixed over one point on Earth, enabling continuous monitoring.
Question 2: What does the term 'radiometric resolution' refer to in remote sensing imagery?
- The number of distinct brightness levels a sensor can detect (Correct answer)
- The smallest ground area a pixel represents
- The range of wavelengths captured by the sensor
- The frequency of image acquisition
Correct answer: The number of distinct brightness levels a sensor can detect
Radiometric resolution describes the number of discrete signal levels (e.g., 8-bit = 256 levels) a sensor can distinguish.
Question 3: In thermal infrared remote sensing, what property of objects is primarily being measured?
- Reflected solar radiation
- Emitted heat energy (Correct answer)
- Absorbed ultraviolet light
- Backscattered radar pulses
Correct answer: Emitted heat energy
Thermal infrared sensors detect heat emitted by objects based on their temperature, not reflected sunlight.
Question 4: Which preprocessing step corrects for differences in sun angle and Earth-Sun distance across an image?
- Geometric correction
- Atmospheric correction
- Radiometric normalization (Correct answer)
- Orthorectification
Correct answer: Radiometric normalization
Radiometric normalization adjusts pixel values to account for varying illumination conditions including sun elevation and Earth-Sun distance.
Question 5: What is 'speckling' in SAR imagery and how is it typically reduced?
- Bright pixels from water bodies, reduced by pan-sharpening
- Salt-and-pepper noise from coherent radar interference, reduced by filtering (Correct answer)
- Striping from detector drift, reduced by destriping algorithms
- Haze from atmosphere, reduced by dark-object subtraction
Correct answer: Salt-and-pepper noise from coherent radar interference, reduced by filtering
Speckle is granular noise inherent to SAR caused by coherent interference of radar waves, commonly reduced with Lee, Frost, or Gamma-MAP filters.
Question 6: Which index is most commonly used to assess vegetation water stress or drought conditions?
- NDVI
- NDWI (Normalized Difference Water Index) (Correct answer)
- EVI
- SAVI
Correct answer: NDWI (Normalized Difference Water Index)
NDWI uses green and NIR bands to detect water content in vegetation canopies, making it effective for monitoring drought stress.
Question 7: In image classification, what distinguishes 'supervised' from 'unsupervised' classification?
- Supervised uses machine learning; unsupervised uses statistics
- Supervised requires analyst-defined training samples; unsupervised clusters pixels automatically (Correct answer)
- Supervised works on multispectral data; unsupervised on hyperspectral
- Supervised is pixel-based; unsupervised is object-based
Correct answer: Supervised requires analyst-defined training samples; unsupervised clusters pixels automatically
Supervised classification uses analyst-provided training areas representing known land cover classes, while unsupervised methods like k-means cluster pixels without prior class definitions.
GIS Remote Sensing and Imagery 2
Which type of satellite orbit provides continuous coverage of the same area on Earth's surface?