F.5.2 Earth infrared

The Earthemitted thermal radiation has a spectrum of a black body with a characteristic average temperature of 288 K. The Earth infrared radiation also varies across the globe but less than the albedo. It also shows a diurnal variation which is small over the ocean but can amount to 20 % for desert areas.

The average infrared radiation emitted by Earth is 230 W m^-2. For an orbiting spacecraft, it can vary from 150 W m^-2 to 350 W m^-2. The diurnal variations can amount to about 20 % over desert areas while being smaller over the oceans.

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

(F-2)

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 the following values are proposed:

e₀= 0,68

e₁ [k₀=0, k₁=-0,07, k₂=0]

e₂= -0,18