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for modelling purposes. Obvious exceptions are glass and water, which are
partially reflecting mirrors and therefore have luminance which is very dependent
on incident light distribution. It is the purpose of this chapter to show how
real surfaces behave as reflectors and to review the methods available for
specifying and measuring surface reflectance.
*A diffuse surface is one which appears of equal luminance from whatever direction it is viewed.
In other words it obeys Lambert’s cosine law1
14.1 General reflection characteristics
14.2 Forms of reflectance
14.3 Practical reflectance data
14.4 Measurement of reflectance
14.5 Implications on modelling
References
15. ATMOSPHERIC ATTENUATION
ln the foregoing chapters all the discussions have made the implicit assumption
that the atmosphere between the object being viewed and the observer is
optically inert and perfect (i.e. it does not affect the luminance, contrast or
quality of the object or scene of interest in any way). Whilst this is usually
assumed to be true in controlled laboratory experiments, it is readily seen not to
be true in some outdoor viewing situations. For instance, when viewing over long
paths it is readily observed that the prevailing meteorological visibility modifies
the scene contrast as a function of range. This is, after all, why there is such a
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