Which of the following will have least spectral reflectance in visible spectrum ? 

The correct answer is 'Water (clear)'

Key Points

• Water (clear):
  • Clear water has the least spectral reflectance in the visible spectrum compared to other natural surfaces.
  • Water absorbs a significant amount of light, especially in the visible spectrum, leading to low reflectance.
  • This characteristic is due to the physical properties of water, which cause it to absorb more and scatter less light, particularly in the blue and green wavelengths.
  • As a result, clear water appears darker in satellite and aerial imagery compared to other surfaces like soil, vegetation, or sand.

Additional Information

• Dry bare soil (grey-brown):
  • Dry bare soil typically has a higher spectral reflectance than water.
  • The reflectance of soil can vary based on moisture content, texture, and organic matter, but generally, dry soil reflects more light across the visible spectrum.
  • Dry soil appears relatively bright in remote sensing imagery.
• Vegetation (green):
  • Vegetation has a characteristic reflectance pattern known as the "red edge," where it reflects strongly in the near-infrared and green wavelengths but absorbs blue and red light.
  • This results in a moderate reflectance in the visible green region, making vegetation appear green to the human eye.
  • Overall, vegetation reflects more light in the visible spectrum compared to clear water.
• Sand:
  • Sand has a high reflectance across the visible spectrum due to its light color and granular texture.
  • It reflects a significant amount of light, making it appear bright in satellite images.
  • This high reflectance is much higher compared to clear water, which absorbs more light.

Important Points

• The spectral reflectance of different surfaces is a crucial factor in remote sensing and environmental monitoring.
• Understanding the reflectance characteristics helps in identifying and classifying various land cover types from satellite and aerial imagery.
• Water bodies, due to their low reflectance, are easily distinguishable from other natural surfaces in remote sensing data.
• This knowledge is applied in various fields, including hydrology, agriculture, and urban planning, to monitor and manage natural resources effectively.