{title2=$\alpha$}
{wiki}

<Albedo> is the fraction of incident <electromagnetic radiation> <power> reflected, summed over the outgoing directions included in the measurement. For incident <power> $P_{\rm in}>0$ and reflected <power> $P_{\rm ref}$,
$$
\alpha=\frac{P_{\rm ref}}{P_{\rm in}},\qquad 0\leq\alpha\leq1.
$$
Thus $\alpha=0.30$ means 30 percent reflected. For an opaque surface the remaining 70 percent is absorbed; for a transmitting layer, transmission must also be accounted for. Specify the incident <wavelengths> and illumination geometry: a visible-band <surface albedo> and a sunlight-weighted broadband <surface albedo> need not agree. NASA's definition explicitly allows a specified spectral band. https://mynasadata.larc.nasa.gov/basic-page/albedo-values[NASA, My NASA Data: Albedo Values]{ref}

For a whole <planet>, broadband <Bond albedo> sums reflected <power> over all outgoing directions and all incident <wavelengths>, weighted by the illuminating spectrum. It is the fraction needed for a whole-planet absorbed-sunlight budget. A local <surface albedo> describes one surface under specified illumination; it cannot simply replace the <Bond albedo> of <Earth>, whose clouds and <terrestrial atmosphere> also reflect and absorb sunlight. Nor is <Bond albedo> the same as <geometric albedo>, which compares brightness in a particular viewing geometry. NASA's account of <Earth>'s budget separates reflection by clouds, particles and the surface from absorption within the <terrestrial atmosphere> and at the surface. https://science.nasa.gov/earth/earth-observatory/climate-and-earths-energy-budget/[NASA Earth Observatory, Climate and Earth's Energy Budget, 2009]{ref}

The usefulness of <albedo> is that it turns optical behavior into an <energy> budget. Bright <snow> and <sea ice> usually absorb less sunlight than exposed water under comparable illumination, but their actual <surface albedos> depend on the spectrum and surface conditions. The <ice-ocean albedo feedback> makes that optical property part of the dynamics, while the following <zero-dimensional planetary energy balance> isolates the geometry and competing <thermal radiation>.


 Albedo (source code)