From Glossary of Meteorology


Used mostly by chemists, the negative logarithm (base 10) of the transmittance of an absorbing sample, often corrected for reflection by its container.

Despite its name, absorbance is a consequence of both scattering and absorption, although scattering is usually assumed to be negligible. To within a constant multiplier, absorbance is absorption optical thickness and depends on the physical thickness of the sample.
Compare absorptance.