Topics in Particle and Dispersion Science

Variability in relationships between the backscattering coefficient and VSF at an angle

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The χ factors obtained by various researchers vary considerably. For example, Vaillancourt et al (2004), by following the procedure of Boss and Pegau (2001) obtained the χ_p = 0.82 for 29 phytoplankton cultures at θ = 141° and a wavelength of 514 nm, compared to χ_p = 1.18 at obtained by Boss and Pegau at θ = 140° and a wavelength of 532 nm. At least part of this reported variability in the χ factors should be due to variations in the optical properties of natural waters.

It has also been postulated that the angular resolution of a nephelometer can affect the magnitude of the χ factor in Eq. 1 (Sullivan et al 2005). Indeed, by using a modified ECO-VSF-1 (WET Labs) nephelometer that measures light scattering at three fixed scattering angles [100°, 125°, and 150°; angular resolution, i.e. field of view (FOV) of ~18°], Sullivan et al obtained the χ factors for the scattering angles of 125° and 150° that were respectively ~20% higher and lower than those found by Boss and Pegau (2001). The results of Boss and Pegau were obtained by using VSF data at a FOV of ≤1°.

Sullivan et al (2005) calculated the backscattering coefficient by numerically integrating a cubic polynomial fitted through the 2πsinθ-weighed VSF data and a value of 0 at θ = 180°, following the method of Moore et al (2000). These latter authors obtained errors of 1-2% with this method for scattering functions measured by Petzold (1972) and claim that the method was more accurate than other methods of fitting the three-point VSF data from ECO-VSF without the 180° zero anchor (M. Twardowski, personal communication).

CITATION: Jonasz M. 2006. Variability in relationships between the backscattering coefficient and VSF at an angle (www.tpdsci.com/Tpc/VsfSwBbAngScaVar.php). In: Top. Part. Disp. Sci. (www.tpdsci.com).

HISTORY: Published: 15-May-2006 Modified: 26-Jun-2006 Peer-reviewed: 15-May-2006

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