Modeling the inherent optical properties of aquatic particles using an irregular hexahedral ensemble

Xu, Guanglang; Sun, Bingqiang; Brooks, Sarah D.; Yang, Ping; Kattawar, George W.; Zhang, Xiaodong

doi:10.1016/j.jqsrt.2017.01.020

Cited by 19 publications

(14 citation statements)

References 37 publications

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“…An analysis to investigate the effect of imperfect fractionation on the results for b p and b bp budgets was performed using theoretical light scattering computations for measured and idealized PSDs. We made these calculations using a particle scattering model of Xu et al () under the assumption that scattering calculations for hexagonally shaped particles can reproduce angular light scattering by natural assemblages of marine particles more adequately than calculations for spherical particles. Adjustment factors describing the fractional difference in theoretical light scattering for idealized fractionation relative to theoretical scattering for actual fractionation were determined as follows:

ξ_{x} = \frac{b_{p x}^{normalI}}{b_{p x}^{normalM}}

ξ_{normalb x} = \frac{b_{bp x}^{normalI}}{b_{bp x}^{normalM}}

where subscript x is the particle‐size fraction (s, m, or l), ξ x and ξ b x are the adjustment factors for b p x and b bp x , respectively, and superscript I or M denotes whether the ideal or measured PSD was used as input for the scattering calculations.…”

Section: Methodsmentioning

confidence: 99%

“…To compute theoretical scattering and backscattering coefficients for our extrapolated measured and idealized PSDs, we first calculated β p ( ψ ) for each PSD. Using an idealized PSD for an example,

β_{p}^{I} ((),, ψ, n) = \sum_{D = 0.2 μ normalm}^{D = 200 μ normalm} N^{I} ((), D) Δ D σ_{b} ((), ψ, n, D),

where D is an equivalent spherical diameter of the center of a given size bin (m), ΔD is the width of the bin (m), N I ( D ) ΔD is the particle number concentration (m −3 ) in the bin as obtained from idealized PSD, n is the assumed complex refractive index of particles relative to water, and σ b is the differential scattering cross section (m 2 sr −1 ) calculated from the particle scattering model (Xu et al ). We integrated the theoretical β p ( ψ ) within the angular range from 0.09° to 150° of LISST‐VSF instrument and used the κ determined from the measured β p ( ψ ) (as described above) to derive theoretical values of b p and b bp .…”

Section: Methodsmentioning

confidence: 99%

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Assessing the effects of particle size and composition on light scattering through measurements of size‐fractionated seawater samples

Koestner

Stramski

Reynolds

2019

Limnology & Oceanography

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Measurements of the particulate volume scattering function, βp(ψ), at light wavelength of 532 nm, particle size distribution, PSD, and several metrics of particulate concentration and composition were made on eight contrasting seawater samples from nearshore and coastal oceanic environments including river estuary and offshore locations. Both βp(ψ) and PSDs were measured on original (unfiltered) samples and particle size‐fractionated samples obtained through filtration using mesh filters with pore sizes of 5 and 20 μm. We present results based on direct size‐fractionated measurements and data adjusted for imperfect fractionation, which provide insights into the roles played by particle size and composition in angle‐resolved light scattering produced by highly variable natural assemblages of aquatic particles. Despite intricate interplay between the effects of particle size and composition, small particles (< 5 μm in size) consistently produced a major or dominant contribution (~ 50–80%) to the particulate backscattering coefficient, bbp, in organic, either phytoplankton or nonalgal, dominated samples regardless of significant variations in PSD between these samples. The notable exception was a sample dominated by large‐celled diatoms from microphytoplankton size range, which exemplifies a scenario when large particles (> 20 μm) can produce a considerable contribution (~ 40%) to bbp. We also observed a trend for inorganic‐dominated samples exhibiting consistently lower contributions (~ 30–40%) of small particles to bbp. The particle size‐based budget for the particulate scattering coefficient, bp, indicates a significant decrease in the role of small particles accompanied by an increase in the role of larger particles compared to the bbp budget.

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ξ_{x} = \frac{b_{p x}^{normalI}}{b_{p x}^{normalM}}

ξ_{normalb x} = \frac{b_{bp x}^{normalI}}{b_{bp x}^{normalM}}

Section: Methodsmentioning

confidence: 99%

β_{p}^{I} ((),, ψ, n) = \sum_{D = 0.2 μ normalm}^{D = 200 μ normalm} N^{I} ((), D) Δ D σ_{b} ((), ψ, n, D),

Section: Methodsmentioning

confidence: 99%

Assessing the effects of particle size and composition on light scattering through measurements of size‐fractionated seawater samples

Koestner

Stramski

Reynolds

2019

Limnology & Oceanography

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“…In Fig. 2, we compare δ p simulated at 532 nm for particles of two very different shapes, sphere versus asymmetrical hexahedron [52,53], of sizes from 1 to ∼300 nm and of two refractive indices, 1.02 and 1.20 relative to the refractive index of water. In addition, we also examined the effect of the FOV of a detector on δ p .…”

Section: E Impact Of Residual Particle Contamination On Light Scattementioning

confidence: 99%

Light scattering by pure water and seawater: the depolarization ratio and its variation with salinity

et al. 2019

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We measured the linearly polarized light scattering of pure water and seawater at various salinities and estimated the depolarization ratio using five different methods of data analysis after removing the scattering due to contamination by residual nanoparticles. The depolarization ratio values (δ) estimated for pure water using these different methods are largely consistent with each other and result in a mean value of 0.039 0.001. For seawater, our results reveal a trend of a slight linear increase of δ with salinity (S), δ 0.039 a 1 × S, where a 1 varies in the range of 1 × 10 −4 to 2 × 10 −4 between the methods.

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“…However, it becomes impractical for large particles due to its excessive demands on the computational power. In contrast, the IGOM is accurate over the range of particle sizes over which the particle size to be much larger than the incident wavelength (Xu et al, 2017).…”

Section: Modeling the Depolarization Ratio Of Water Droplets Aerosolmentioning

confidence: 98%

Using depolarization to quantify ice nucleating particle concentrations: a new method

Zenker

Collier

et al. 2017

Atmos. Meas. Tech.

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Abstract. We have developed a new method to determine ice nucleating particle (INP) concentrations observed by the Texas A&M University continuous flow diffusion chamber (CFDC) under a wide range of operating conditions. In this study, we evaluate differences in particle optical properties detected by the Cloud and Aerosol Spectrometer with POLarization (CASPOL) to differentiate between ice crystals, droplets, and aerosols. The depolarization signal from the CASPOL instrument is used to determine the occurrence of water droplet breakthrough (WDBT) conditions in the CFDC. The standard procedure for determining INP concentration is to count all particles that have grown beyond a nominal size cutoff as ice crystals. During WDBT this procedure overestimates INP concentration, because large droplets are miscounted as ice crystals. Here we design a new analysis method based on depolarization ratio that can extend the range of operating conditions of the CFDC. The method agrees reasonably well with the traditional method under non-WDBT conditions with a mean percent error of ±32.1 %. Additionally, a comparison with the Colorado State University CFDC shows that the new analysis method can be used reliably during WDBT conditions.

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Modeling the inherent optical properties of aquatic particles using an irregular hexahedral ensemble

Cited by 19 publications

References 37 publications

Assessing the effects of particle size and composition on light scattering through measurements of size‐fractionated seawater samples

Assessing the effects of particle size and composition on light scattering through measurements of size‐fractionated seawater samples

Light scattering by pure water and seawater: the depolarization ratio and its variation with salinity

Using depolarization to quantify ice nucleating particle concentrations: a new method

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