GIS Remote Sensing and Imagery 4 — Questions and Answers
Question 1: What is 'pan-sharpening' in remote sensing image processing?
- Removing haze from imagery using the panchromatic band
- Merging a high-resolution panchromatic band with lower-resolution multispectral bands to create a high-resolution color image (Correct answer)
- Georeferencing an image using ground control points
- Applying a high-pass filter to enhance edges
Correct answer: Merging a high-resolution panchromatic band with lower-resolution multispectral bands to create a high-resolution color image
Pan-sharpening fuses the spatial detail of a high-resolution panchromatic band with the color information of coarser multispectral bands to produce a higher-resolution color composite.
Question 2: In remote sensing, what does the 'bidirectional reflectance distribution function' (BRDF) describe?
- The relationship between image resolution and revisit time
- How a surface reflects light differently depending on view and illumination angles (Correct answer)
- The ratio of absorbed to emitted energy by a surface
- The spectral response function of a satellite sensor
Correct answer: How a surface reflects light differently depending on view and illumination angles
BRDF characterizes how a surface reflects incoming radiation as a function of both the illumination direction and the viewing direction.
Question 3: Which satellite sensor family is specifically designed for global forest change detection and widely used in Hansen's Global Forest Change dataset?
- MODIS Terra/Aqua
- Landsat series (Correct answer)
- Sentinel-1 SAR
- GOES-East
Correct answer: Landsat series
Hansen's Global Forest Change dataset uses Landsat imagery due to its decades-long archive, 30m resolution, and free global availability.
Question 4: What distinguishes 'active' from 'passive' remote sensing systems?
- Active systems record reflected sunlight; passive systems emit their own energy
- Active systems emit their own energy; passive systems detect naturally occurring energy (Correct answer)
- Active systems use optical sensors; passive systems use radar
- Active systems are airborne; passive systems are spaceborne
Correct answer: Active systems emit their own energy; passive systems detect naturally occurring energy
Active remote sensing systems (like radar and LiDAR) emit their own energy and record the return signal, while passive systems record energy from natural sources like the sun.
Question 5: What is the primary use of the shortwave infrared (SWIR) bands in multispectral remote sensing?
- Detecting urban heat islands
- Discriminating between soil moisture, rock types, and cloud vs. snow (Correct answer)
- Measuring ocean surface temperature
- Detecting atmospheric ozone concentrations
Correct answer: Discriminating between soil moisture, rock types, and cloud vs. snow
SWIR bands (1.3–2.5 µm) are sensitive to mineral composition, soil moisture, and can distinguish snow (absorbs SWIR) from clouds (reflects SWIR).
Question 6: When performing image-to-image co-registration, what is the goal?
- Converting image pixel values to surface reflectance
- Aligning multiple images of the same area so pixels correspond to the same geographic locations (Correct answer)
- Merging overlapping image strips into a single mosaic
- Removing atmospheric haze from multi-date imagery
Correct answer: Aligning multiple images of the same area so pixels correspond to the same geographic locations
Co-registration aligns two or more images geometrically so that each pixel represents the same point on the ground, which is essential for change detection and time-series analysis.
Question 7: What is the significance of the 'red edge' spectral region (~700–730 nm) in vegetation remote sensing?
- It corresponds to strong chlorophyll absorption used for stress detection
- It marks the transition between chlorophyll absorption and high NIR reflectance, sensitive to vegetation health (Correct answer)
- It is used to detect bare soil and mineral content
- It corresponds to the peak reflectance of water bodies
Correct answer: It marks the transition between chlorophyll absorption and high NIR reflectance, sensitive to vegetation health
The red edge is the steep reflectance transition between chlorophyll absorption in red and the leaf cell structure reflection plateau in NIR, and its position shifts with plant stress or LAI changes.
GIS Remote Sensing and Imagery 4
What is 'pan-sharpening' in remote sensing image processing?