CH Remote Sensing & Satellite Imagery 1 — Questions and Answers
Question 1: What does LiDAR stand for in the context of hydrographic remote sensing?
- Light Detection And Ranging (Correct answer)
- Linear Distance And Range
- Land Imaging Detection And Reconnaissance
- Laser Intensity Detection And Ranging
Correct answer: Light Detection And Ranging
LiDAR stands for Light Detection And Ranging, using laser pulses to measure distances and, in bathymetric applications, water depths.
Question 2: Which type of satellite sensor is most commonly used to measure sea surface temperature (SST) in hydrographic studies?
- Synthetic Aperture Radar (SAR)
- Thermal Infrared (TIR) sensor (Correct answer)
- Multispectral optical sensor
- Photon-counting LiDAR
Correct answer: Thermal Infrared (TIR) sensor
Thermal infrared sensors detect heat emission from the ocean surface, making them the standard tool for sea surface temperature measurement from satellites.
Question 3: What is the primary advantage of multispectral satellite imagery for shallow water bathymetry?
- It operates in all weather conditions including heavy cloud cover
- It can penetrate clear, shallow water to map the seafloor using light attenuation (Correct answer)
- It can measure depths greater than 200 meters in open ocean
- It requires no ground truth calibration data
Correct answer: It can penetrate clear, shallow water to map the seafloor using light attenuation
Multispectral imagery exploits differential attenuation of light wavelengths through clear water, enabling seafloor mapping in shallow, transparent conditions typically up to 20–25 m depth.
Question 4: Synthetic Aperture Radar (SAR) is particularly valuable for hydrographic applications because it can:
- Measure water depth in turbid estuarine conditions
- Detect oil spills, ship wakes, and surface roughness regardless of cloud cover or darkness (Correct answer)
- Accurately measure sea surface temperature in real time
- Map the seafloor in waters deeper than 500 meters
Correct answer: Detect oil spills, ship wakes, and surface roughness regardless of cloud cover or darkness
SAR operates in the microwave spectrum, penetrating clouds and functioning day or night, making it ideal for detecting surface phenomena such as oil spills, ship wakes, and internal waves.
Question 5: The Secchi depth is used in satellite-derived bathymetry primarily to estimate:
- Maximum sonar detection range beneath the vessel
- Water transparency and maximum depth of optical light penetration (Correct answer)
- Tidal range at a coastal survey site
- Depth of the thermocline layer
Correct answer: Water transparency and maximum depth of optical light penetration
Secchi depth quantifies water transparency by measuring how deep a white disk remains visible, indicating how far light penetrates and thus the practical depth limit for optical satellite bathymetry.
Question 6: The Normalized Difference Water Index (NDWI) is primarily used in remote sensing to:
- Measure salinity concentration gradients in coastal waters
- Distinguish and delineate water bodies from land and vegetation (Correct answer)
- Calculate significant wave height from radar imagery
- Detect submerged aquatic vegetation density
Correct answer: Distinguish and delineate water bodies from land and vegetation
NDWI uses the ratio of green and near-infrared bands to highlight water bodies, since water strongly absorbs NIR while land and vegetation reflect it strongly.
Question 7: Which orbit type do most hydrographic Earth observation satellites use to achieve consistent global coverage?
- Geostationary orbit at 35,786 km altitude
- Sun-synchronous Low Earth Orbit (LEO) (Correct answer)
- Medium Earth Orbit (MEO) used by GPS satellites
- Highly Elliptical Orbit (HEO)
Correct answer: Sun-synchronous Low Earth Orbit (LEO)
Sun-synchronous LEO orbits ensure the satellite crosses each latitude at the same local solar time, providing consistent illumination conditions and global coverage with frequent revisits.
CH Remote Sensing & Satellite Imagery 1
What does LiDAR stand for in the context of hydrographic remote sensing?