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Title: Variability of relationship between the volume scattering function at 180° and the backscattering coefficient for aquatic particles

Properly interpreting lidar (light detection and ranging) signal for characterizing particle distribution relies on a key parameter,χ<#comment/>p(π<#comment/>), which relates the particulate volume scattering function (VSF) at 180° (β<#comment/>p(π<#comment/>)) that a lidar measures to the particulate backscattering coefficient (bbp). However,χ<#comment/>p(π<#comment/>)has been seldom studied due to challenges in accurately measuringβ<#comment/>p(π<#comment/>)andbbpconcurrently in the field. In this study,χ<#comment/>p(π<#comment/>), as well as its spectral dependence, was re-examined using the VSFs measuredin situat high angular resolution in a wide range of waters.β<#comment/>p(π<#comment/>), while not measured directly, was inferred using a physically sound, well-validated VSF-inversion method. The effects of particle shape and internal structure on the inversion were tested using three inversion kernels consisting of phase functions computed for particles that are assumed as homogenous sphere, homogenous asymmetric hexahedra, or coated sphere. The reconstructed VSFs using any of the three kernels agreed well with the measured VSFs with a mean percentage difference<<#comment/>5%<#comment/>at scattering angles<<#comment/>170∘<#comment/>. At angles immediately near or equal to 180°, the reconstructedβ<#comment/>p(π<#comment/>more » stretchy='false'>)depends strongly on the inversion kernel.χ<#comment/>p(π<#comment/>)derived with the sphere kernels was smaller than those derived with the hexahedra kernel but consistent withχ<#comment/>p(π<#comment/>)estimated directly from high-spectral-resolution lidar andin situbackscattering sensor. The possible explanation was that the sphere kernels are able to capture the backscattering enhancement feature near 180° that has been observed for marine particles.χ<#comment/>p(π<#comment/>)derived using the coated sphere kernel was generally lower than those derived with the homogenous sphere kernel. Our result suggests thatχ<#comment/>p(π<#comment/>)is sensitive to the shape and internal structure of particles and significant error could be induced if a fixed value ofχ<#comment/>p(π<#comment/>)is to be used to interpret lidar signal collected in different waters. On the other hand,χ<#comment/>p(π<#comment/>)showed little spectral dependence.

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Publication Date:
Journal Name:
Applied Optics
Page Range or eLocation-ID:
Article No. C31
1559-128X; APOPAI
Optical Society of America
Sponsoring Org:
National Science Foundation
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