Snow optics — wavelength band where albedo depends strongly on grain size The semi-infinite snow albedo is approximately proportional to the square root of grain radius most strongly in which spectral band?

Introduction / Context:
Snow reflectance varies with wavelength and microstructure. In the visible, fresh snow is highly reflective with relatively weak sensitivity to grain size. In the near-infrared (NIR), absorption by ice increases and scattering paths depend sensitively on grain radius, making albedo strongly grain-size dependent.

Given Data / Assumptions:

• Optically thick (semi-infinite) snowpack.
• Dry snow, neglecting liquid water and soot/dust impurities.
• Looking for the band where albedo vs. grain size dependence is strongest.

Concept / Approach:

Radiative transfer models show that in the NIR the absorption coefficient of ice rises, so photons undergo fewer scatterings and the mean free path scales with grain size. Empirical parameterizations often express albedo ∝ sqrt(r_g) or similar functional dependence in NIR windows, capturing the observed rapid albedo decrease as grains coarsen (metamorphism).

Step-by-Step Solution:

Verification / Alternative check:

Snow albedo spectra commonly show steep decline beyond ~0.8 μm; remote sensing of snow grain size exploits NIR/SWIR bands for this reason.

Why Other Options Are Wrong:

• UV and visible bands exhibit much higher, less grain-size-sensitive albedo for clean snow.
• “None of these” contradicts established snow optics behavior.

Common Pitfalls:

• Ignoring impurity effects (black carbon/dust) which also reduce albedo, especially in visible.
• Confusing “grain radius” dependence with snow depth dependence.

Final Answer:

0.8 to 1.2 μm (near-infrared).