"For a smooth surface such as glass, most of the radiation is
reflected from the surface by regular or specular reflection
and no absorption takes place. In the 1100–2500nm
region, the amount of scattering makes the path length
so great that transmittance through 1 cm of most samples
is negligible. This situation is called diffuse reflectance
because most of the incident radiation is reflected. If a
matt surface reflects diffusely without penetration into
the sample, like specular reflectance no absorption takes
place. If, however, some of the radiation penetrates the
surface when it reaches each particle it can be reflected,
absorbed or transmitted. The net result is that the diffusely
reflected radiation (R) can be empirically related to
concentration (c) in an analogous way to Beer’s law
i.e. log 1=R D kc where k is a factor which incorporates
both absorbtivity and path length."
((NEAR-INFRARED SPECTROSCOPY IN FOOD ANALYSIS 1
Near-infrared Spectroscopy
in Food Analysis
Brian G. Osborne
BRI Australia Ltd, North Ryde, Australia))
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