17-1225

spectral optical depth (of a medium, for a given length) [δ(λ)]

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 depth, 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

Equivalent term: "spectral optical thickness"

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:

        

so that

         .

NOTE 2 For a homogeneous non-diffusing layer, δ(λ) is the Napierian spectral internal transmittance density.

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