A Sentinel-2 image shows pixels that appear bright in the near-infrared band and dark in the red band. What surface type does this pattern most likely represent?
AOpen water, which absorbs infrared radiation
BBare soil, which reflects evenly across visible and infrared
CHealthy green vegetation, which strongly reflects NIR and absorbs red light for photosynthesis
DSnow, which reflects strongly across all visible wavelengths
Healthy vegetation has a characteristic spectral signature: chlorophyll absorbs red light for photosynthesis while leaf mesophyll cell structure strongly scatters near-infrared radiation. This dramatic contrast is the basis of vegetation indices like NDVI.
Question 2 True / False
Higher spatial resolution in optical remote sensing always produces better results for land cover classification.
TTrue
FFalse
Answer: False
Higher spatial resolution increases detail but also increases spectral variability within land cover classes (the salt-and-pepper effect). A 30m pixel averages many trees into a smooth signature, while a 0.5m image shows individual crowns, shadows, and gaps. The optimal resolution depends on the application.
Model answer: The signal includes both surface-reflected radiation and unwanted atmospheric contributions: Rayleigh scattering adds bluish haze, aerosol scattering adds path radiance, and atmospheric gases absorb portions of the signal. Atmospheric correction models estimate and remove these effects to retrieve physically meaningful surface reflectance values comparable across dates and sensors.
Raw satellite digital numbers are contaminated by atmosphere. Atmospheric correction converts them to surface reflectance.