F.5.1 Earth albedo

The fraction of incident sunlight that is reflected off a planet is termed albedo. For an orbiting spacecraft the albedo value depends mainly on the sunlit part of the Earth which it can see. Albedo radiation has approximately the same spectral distribution as the Sun and in this Standard albedo refers to the total solar spectrum albedo. Albedo is highly variable across the globe and depends on surface properties and cloud cover. It also depends on the solar zenith angle. Average albedo values have sometimes to be used with care, e.g. for short duration analyses or for Sunsynchronous orbits where albedo is from specific local times.

The average albedo of the Earth is 0,3. For an orbiting spacecraft, the albedo can vary between 0,05 (open ocean) and 0,6 (high cloud/icecap).

A model has been constructed for estimating the influence of latitude and longitude on albedo variability (seasonal effect) [RD.34]. The albedo, a, is given by:

(F-1)

where

t₀ is the date

ω is the orbital pulsation (=2π/365,25)

ϕ is the equatorial latitude

JD is the Julian date of interest

P_n is the n^th degree Legendre polynomial

and

a₀=0,34

a₁ [c₀=0, c₁=0,10, c₂=0]

a₂=0,29