Snow Cover – Reflectance and grain size variability Which statements about snow cover on Earth's surface are correct regarding spectral reflectance and physical variability?

Introduction / Context:
Snow albedo strongly influences surface energy balance and hydrologic forecasts. Remote sensing leverages snow's bright visible reflectance and darker SWIR response, but both are modulated by grain size and impurities such as dust or soot.

Given Data / Assumptions:

• Natural snowpacks of varying age and cleanliness.
• Spectral regions spanning visible and SWIR.
• Typical solar illumination conditions.

Concept / Approach:
Fresh, clean snow is among the brightest terrestrial targets in visible bands. As grains grow (metamorphism) or contaminants accumulate, visible reflectance decreases and SWIR absorption changes, altering indices such as NDSI (which contrasts visible and SWIR bands). Grain size governs path length within ice, directly affecting absorption and scattering.

Step-by-Step Solution:
Identify baseline: very high visible reflectance versus soil/vegetation.Account for variability: age, melt–freeze cycles, impurities reduce reflectance and increase SWIR absorption.Relate to physics: larger grains increase effective absorption path ⇒ darker appearance in NIR/SWIR.

Verification / Alternative check:
Operational snow products exploit visible–SWIR contrast; changes in grain size/impurities are monitored using multi-temporal reflectance trends.

Why Other Options Are Wrong:

• Each of (a), (b), and (c) holds for real snowpacks; thus “All of the above” is correct.
• “None of these” contradicts well-established snow optics.

Common Pitfalls:
Assuming snow reflectance is constant irrespective of aging; in practice it evolves rapidly with weather and deposition.

Final Answer:
All of the above