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

Zhang, Xiaodong; Stramski, Dariusz; Reynolds, Rick A.; Blocker, E. Riley

doi:10.1364/ao.58.000991

Cited by 25 publications

(18 citation statements)

References 47 publications

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“…where δ is the depolarization ratio of pure seawater and β sw (90 o , δ) is the unpolarized pure seawater VSF at 90°. In this study, δ is set equal to 0.039 as suggested by various studies (Farinato and Rowell 1976;Jonasz and Fournier 2007;Werdell et al, 2018;Zhang et al, 2019), and β sw (90 o , δ) was computed according to (Zhang et al, 2009).…”

Section: Dolpmentioning

confidence: 99%

The Degree of Linear Polarization for Suspended Particle Fields from Diverse Natural Waters

Zhai

Twardowski

2021

Front. Remote Sens.

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The Degree of Linear Polarization (DoLP) for unperturbed particle fields in waters from six diverse regions around the globe was measured with the custom Multi-Angle Scattering Optical Tool (MASCOT). DoLP here is defined as the ratio of two elements of Mueller scattering matrix, i.e., -M12/M11. Field sites covered inland waters, coastal oceans and open oceans, including both ocean color Case I and II water types. The angular shape of the measured particulate DoLP was analyzed in detail for each field site and for the ensemble average. Three parameters used to quantitatively characterize DoLP shape were the symmetry with respect to 90°, peak magnitude, and peak angle of measured DoLP angular curve. Vertical profiles of particulate DoLP were analyzed with maximum recorded depth of 111 m. Converse to Rayleigh scatterers, we found measured particulate DoLPs were not symmetric with respect to 90°. On average, DoLP peaks were shifted slightly toward larger angles, with most falling between estimated values of 90° and 95°. All particulate DoLP peak magnitudes generally varied within [0.6, 0.9]. Lorenz-Mie (homogeneous sphere) light scattering theory was used to construct a new inversion for bulk particulate refractive index from a lookup table based on DoLP and spectral attenuation measurements. We compared the Mie-DoLP-based particulate refractive index retrieval with the backscattering-based model from (Twardowski et al., J. Geophys. Res., 2001, 106(C7), 14,129–14,142). Particulate refractive index retrieved with the two models were in some cases comparable. At two of the six field sites we saw good agreement between the two models, whereas at another two field sites we observed large discrepancies between the two models. Further investigation on the choice of the modeled particle shapes and compositions may improve this retrieval approach. Results are compatible with previous studies on DoLPs in natural waters and comprehensive observations are provided on the particulate DoLP angular shape, vertical profile and global distributions that are important for future vector radiative transfer simulations. This study is relevant to future PACE polarimeters and associated remote retrieval of oceanic particle composition using polarimetry.

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Section: Dolpmentioning

confidence: 99%

The Degree of Linear Polarization for Suspended Particle Fields from Diverse Natural Waters

Zhai

Twardowski

2021

Front. Remote Sens.

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“…Nonetheless, this important parameter deserves additional experimental evaluation to further reduce uncertainties in pure water scattering values. Very recently, Zhang et al (2019) measured, δ m of pure water and seawater at various salinities. They obtained δ m = 0.039±0.001 for pure water, which supports the currently adopted value of 0.039.…”

Section: Molecular Scattering Pace Discussion (Fwd Rt Studies): Purementioning

confidence: 99%

Modeling Atmosphere-Ocean Radiative Transfer: A PACE Mission Perspective

et al. 2019

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The research frontiers of radiative transfer (RT) in coupled atmosphere-ocean systems are explored to enable new science and specifically to support the upcoming Plankton, Aerosol, Cloud ocean Ecosystem (PACE) satellite mission. Given (i) the multitude of atmospheric and oceanic constituents at any given moment that each exhibits a large variety of physical and chemical properties and (ii) the diversity of light-matter interactions (scattering, absorption, and emission), tackling all outstanding RT aspects related to interpreting and/or simulating light reflected by atmosphere-ocean systems becomes impossible. Instead, we focus on both theoretical and experimental studies of RT topics important to the science threshold and goal questions of the PACE mission and the measurement capabilities of its instruments. We differentiate between (a) forward (FWD) RT studies that focus mainly on sensitivity to influencing variables and/or simulating data sets, and (b) inverse (INV) RT studies that also involve the retrieval of atmosphere and ocean parameters. Our topics cover (1) the ocean (i.e., water body): absorption and elastic/inelastic scattering by pure water (FWD RT) and models for scattering and absorption by particulates (FWD RT and INV RT); (2) the airwater interface: variations in ocean surface refractive index (INV RT) and in whitecap reflectance (INV RT); (3) the atmosphere: polarimetric and/or hyperspectral remote sensing of aerosols (INV RT) and of gases (FWD RT); and (4) atmosphere-ocean systems: benchmark comparisons, impact of the Earth's sphericity and adjacency effects on space-borne observations, and scattering in the ultraviolet regime (FWD RT). We provide for each topic a summary of past relevant (heritage) work, followed by a discussion (for unresolved questions) and RT updates.

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“…I ij calculated from Eq. (2) are related to the Mueller scattering matrix elements of P 11 (i.e., VSF), P 12 , and P 22 [37,38] as:…”

Section: Overview Of Data Processing Of the Lisst-vsf Eyeball Measurementioning

confidence: 99%

Calibration of the LISST-VSF to derive the volume scattering functions in clear waters

Zhang

Xiong

et al. 2019

Opt. Express

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The recently commercialized LISST-VSF instrument measures the volume scattering function (VSF) from 0.1°to 15°with a traditional laser diffraction unit (LISST) and from 15°to 155°with an eyeball component. Between these two optical components, only the LISST unit is calibrated. The eyeball measurements are scaled using the VSFs at 15°that are measured by both components. As this relative calibration relies on a valid measurement at 15°by the LISST, it might fail in clear oceanic waters, where the forward scattering is relative weak either due to a lack of large particles or an overall low concentration of all particles. In this study, we calibrated the LISST-VSF eyeball component through a series of lab experiments using standard polystyrene beads. Validation with the beads of two different sizes showed a median difference of 11.1% between theoretical and calibrated values. Further evaluations with in situ data collected by the LISST-VSF and an ECO-BB3 meter indicated that the new calibration worked well in both turbid and clear waters, while the relative calibration method tended to overestimate VSFs in clear waters.

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

Cited by 25 publications

References 47 publications

The Degree of Linear Polarization for Suspended Particle Fields from Diverse Natural Waters

The Degree of Linear Polarization for Suspended Particle Fields from Diverse Natural Waters

Modeling Atmosphere-Ocean Radiative Transfer: A PACE Mission Perspective

Calibration of the LISST-VSF to derive the volume scattering functions in clear waters

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