Zenith Sky Optical Thickness Infrared Spectrum
Zenith absorption, A is the fraction of incident electromagnetic energy which is absorbed by the atmosphere at a given wavelength on a directly vertical path from the Earth's surface to space. It is a dimensionless quantity ranging from A = 0 (full transmission) to A = 1 (full absorption).
Zenith optical thickness, τ can be calculated from the absorption as τ = - ln(1-A). Optical thickness is dimensionless and always ≥ 0, with larger values corresponding to stronger absorption.
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