Snow Optics – Spectral reflectance behaviour of fresh, pure snow In remote sensing of cryosphere, how does the reflectance of fresh and pure snow vary across the spectrum (visible, near-IR, and longer wavelengths)?

Introduction / Context:
Fresh, clean snow has a distinctive spectral signature that underpins snow mapping, albedo estimation, and melt monitoring from satellites. Understanding how reflectance changes from the visible through the near-infrared (near-IR) into the shortwave and thermal infrared helps choose optimal bands and interpret seasonal trends in cryospheric products.

Given Data / Assumptions:

• Target: fresh, pure (clean) snow with small grain size.
• Spectral regions: visible (~0.4–0.7 μm), near-IR (~0.7–1.3 μm), and longer wavelengths (shortwave IR >1.4 μm to thermal IR).
• Typical solar-reflective remote sensing conditions.

Concept / Approach:
Snow's high visible reflectance arises from multiple scattering by air–ice interfaces in fine grains. As wavelength increases into the near-IR, ice absorption increases, reducing reflectance. In the shortwave IR beyond ~1.4 μm, strong absorption bands make reflectance low; thermal IR is governed by emission rather than reflection.

Step-by-Step Solution:
Visible: strong multiple scattering ⇒ high reflectance (bright snow).Near-IR: increasing ice absorption coefficient ⇒ reflectance decreases rapidly.Longer wavelengths (SWIR/TIR): strong absorption and thermal emission dominance ⇒ low apparent reflectance.

Verification / Alternative check:
Common snow indices (e.g., using a green/near-IR or red/SWIR contrast) exploit snow's bright-in-visible, dark-in-SWIR behaviour for robust discrimination from clouds/soil.

Why Other Options Are Wrong:

• a, b, c each describe a correct portion of the spectrum; hence the combined choice “All of these” is correct.
• “None of these” contradicts established snow spectra.

Common Pitfalls:
Confusing dirty/old snow (lower visible reflectance) with fresh snow, or assuming near-IR stays high like vegetation; in snow it falls markedly.

Final Answer:
All of these