Where does albedo collide?

In climate physics, albedo is the fraction of incoming solar radiation that a surface or the whole planet reflects back to space instead of absorbing, a dimensionless number running from 0 for a perfect absorber to 1 for a perfect reflector. Bright snow and ice reflect strongly and dark ocean and forest weakly, so a warming that melts ice lowers the albedo and lets the ground soak up still more heat, the loop that Budyko's 1969 The effect of solar radiation variations on the climate of the Earth built into an early energy-balance model of the ice ages. Here the meaning is a reflectance ratio that governs Earth's heat budget, not a white tissue in a fruit, a chance that a neutron bounces back, or a number for how bright a distant planet looks.[1]

Unit

A dimensionless reflectance from 0 to 1, for a surface or the whole planet

Recovery means

Not applicable

Measured by

Measured by pyranometers at the ground and by satellite radiometers as reflected over incoming shortwave radiation

In astronomy, the albedo of a planet, moon, or asteroid is the ratio of the light it reflects to the light that falls on it, used to read a body's size, surface, and make-up from how bright it appears. Astronomers separate the geometric albedo, the brightness at full illumination compared with a perfectly diffusing disk of the same size, from the Bond albedo, the fraction of all incident light thrown back in every direction, a distinction that Russell's 1916 On the Albedo of the Planets and Their Satellites laid out while estimating these values across the solar system. Here the meaning is a whole-body reflectance inferred from starlight or sunlight, not a surface term in a climate model, a white layer of peel, or the return of neutrons at a wall.[2]

Unit

A dimensionless ratio, geometric or Bond, for a whole body

Recovery means

Not applicable

Measured by

Derived from photometry of the body's brightness across phase angles together with its measured size

In reactor physics, the neutron albedo is the fraction of neutrons hitting a boundary that are scattered back into the region they came from, a reflection coefficient used to model the reflectors that bounce escaping neutrons back into a reactor core. It enters diffusion theory as a boundary condition and is worked out for candidate reflector materials, as in Azimkhani, Zolfagharpour, and Ziaie's 2018 calculation of thermal neutron albedo for mono-material and bi-material reflectors. Here the meaning is a return probability for neutrons at an interface, not the reflectance of sunlight by a surface or a planet, and not the white flesh of a citrus peel.[3]

Unit

A dimensionless return probability from 0 to 1, at a material boundary

Recovery means

Not applicable

Measured by

Computed from diffusion or transport theory and measured by counting neutrons reflected from a slab of material