“…All methods presently in use make some assumptions in order to measure the absorption coefficient; the most frequently applied are listed among the following: integrating sphere (Fischer, 1970;Weintzenberg, 1982), integrating plate (Lin et al, 1973;Weiss et al, 1979;Stevens et al, 1982), integrating sandwich , laser transmission method (Rosen et al, 1978), photoacoustic methods (Yasa et al, 1979;Stevens et al, 1982), and powder technology methods (Kortiim, 1969;Lindberg and Laude, 1974). Intercomparison of the different methods gives considerable disagreement: the integrating plate method and laser transmission method differ by a factor of 2.5 although they are highly correlated (Sadler et al, 1981), the laser transmission method giving higher values.…”