Snow optics: how does increasing snow grain size affect albedo across wavelengths, and in which spectral region is this effect strongest?

Introduction / Context:Snow albedo critically influences surface energy balance and melt. Remote sensing retrievals of snow properties rely on predictable changes in reflectance with grain size, impurities, and liquid water content. This question focuses on the canonical effect of grain coarsening on albedo across wavelengths.

Given Data / Assumptions:

• We compare fine-grained fresh snow to coarser, metamorphosed snow.
• Wavelength regions considered: visible (VIS) and near-infrared (NIR).
• No soot/dust contamination; effect attributed primarily to grain size.

Concept / Approach:As snow grains become larger, the path length of photons within the ice matrix increases, raising the probability of absorption (particularly in NIR where ice absorption is stronger). Consequently, albedo decreases with grain growth across most bands, but the drop is most pronounced in near-IR; visible bands are less sensitive because absorption by pure ice is weak there, so reflectance remains relatively high though it can still decline modestly.

Step-by-Step Solution:Recognize the general trend: increasing grain size → lower albedo.Identify spectral dependence: strongest decline in NIR due to higher ice absorption.Visible response is weaker but still negative; hence “low in visible.”All three statements are simultaneously true, so choose “All of these.”

Verification / Alternative check:Snow reflectance spectra show steep NIR decreases as grains grow; algorithms such as NDSI leverage visible–NIR contrast.

Why Other Options Are Wrong:

• Claiming only VIS increases contradicts physical absorption behaviour.

Common Pitfalls:Attributing albedo changes solely to impurity content; overlooking the spectral variability of ice absorption coefficients.

Final Answer:All of these