| quantity used in atmospheric physics and physical oceanography : for a monochromatic component of wavelength λ of the radiation of a collimated beam propagating along the given length from the point x1 to the point x2 on its path through a homogeneous or non-homogeneous diffusing medium, the spectral optical thickness δ(λ) of the medium between x1 and x2 is defined by the formula|
where μ(x,λ) is the spectral linear attenuation coefficient at the location of dx
unit : 1
Note 1 – The spectral radiant flux Φe, λ (x1, λ) of the beam at the point x1 is reduced to the value of Φe, λ (x2, λ) at the point x2 according to the formula
Note 2 – For a homogeneous non-diffusing layer, δ(λ) is the Napierian spectral internal transmittance density.