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Given a finite acceptance angle of the detector in an experimental arrangement for measuring the attenuation of light by a light absorbing and scattering medium (see Acceptance angle of the detector and Limiting of the acceptance angle ...), some scattered light is unavoidably admitted by the detector. Hence, the evaluation of the accuracy of such measurements must involve an estimation of the contribution of the scattered light to the power received by the detector.
The experimental arrangements discussed here employ a laser-light source which generates a highly collimated light beam. With the lens-aperture limiting system for the detector acceptance angle (Fig. 1 in Limiting the acceptance angle of the detector), this simplifies the interpretation of the light-scattering-related error of the transmission measurements (for example, Voss KJ and Austin 1993). Indeed, in this case, the detector acceptance angle is the same for the entire sample, assuming that the lens has a sufficiently large diameter to avoid vignetting of that angle. In other cases, including the cylindrically-limited transmissometer design (for example, Voss KJ and Austin 1993) using an extended-area light source, the acceptance angle may vary with the position of the elementary scattering volume within the sample (see also Fig. 2 in Limiting the acceptance angle of the detector, and Wind L and Szymanski 2002, Deepak A and Box 1978a). This complicates evaluation of the contribution of scattered light admitted by the detector.
The scattering correction for the attenuation measurements in natural waters is discussed by, for example, Piskozub J et al 2004, Voss KJ and Austin 1993, and Zaneveld JRV and Bartz 1984 . Wind L and Szymanski 2002, Deepak A and Box 1978b (polydispersions), 1978a (monodispersions), Zardecki A (1983), Tam WG and Zardecki 1982b and 1982a discuss the scattering corrections for atmospheric aerosols. In particular, Deepak A and Box, Zardecki A and Tam WG, and Zardecki discuss the corrections for two cases of the detector acceptance angle: an "open" detector with the hemispherical acceptance angle, and a detector with a more strictly limited (variable) acceptance angle.
See also Lambert's law: Scattering corrections and the index entry: attenuation of light, coefficient, measurement for additional references.
| CITATION: Swanson N. L., Jonasz M. 2007. Measuring attenuation of light: Scattering correction (www.tpdsci.com/Tpc/AtnCfMsScaCor.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 21-Nov-2007 Modified: 17-Jan-2008 Peer-reviewed: 22-Dec-2007 |
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