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首页> 外文期刊>Applied optics >Retrieving composition and sizes of oceanic particle subpopulations from the volume scattering function
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Retrieving composition and sizes of oceanic particle subpopulations from the volume scattering function

机译：从体积散射函数中检索海洋粒子亚群的组成和大小

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摘要

For a particle population with known size, composition, structure, and shape distributions, its volume scattering function (VSF) can be estimated from first principles through a governing relationship, the Fredholm linear integral equation of the first kind. Inverting the Fredholm equation to derive the composition and size distribution of particles from measured VSFs remains challenging because 1) the solution depends on the kernel function, and 2) the kernel function needs to be constructed to avoid singularity. In this study, a thorough review of the earlier and current inversion techniques is provided. An inversion method based on nonnegative least squares is presented and evaluated using the VSFs measured by a prototype volume scattering meter at the LEO-15 site off the New Jersey coast. The kernel function was built by a compilation of individual subpopulations, each of which follows a lognormal size distribution and whose characteristic size and refractive index altogether cover the entire ranges of natural variability of potential marine particles of the region. Sensitivity analyses were conducted to ensure the kernel function being constructed is neither singular nor pathological. A total of 126 potential subpopulations were identified, among which 11 are common in more than half of the inversions and only five consistently present (>90percent of measurements). These five subpopulations can be interpreted as small colloidal type particles of sizes around 0.02 (mu)m, submicrometer detritus-type particles (n_(r) velence 1.02, r_(mode) velence 0.2(mu)m), two micrometer-sized subpopulations with one relatively soft (n_(r) velence 1.04 and r_(mode) velence 1.6 (mu)m) and the other relatively refringent (n_(r) velence 1.10 and r_(mode) velence 3.2 (mu)m), and bubbles of relatively large sizes (n_(r) velence 0.75 and r_(mode) velence 10(mu)m). Reconstructed PSDs feature a bimodal shape, with the smaller peak dominated by the colloidal subpopulations and the larger particles closely approximated by a power-law function. The Junge-type slope averages -4.0 +- 0.2, in close agreement with the well-known mean value of -4.0 over the global ocean. The distribution of the refractive index suggested a dominance of particles of higher water content, also in agreement with earlier results based on the backscattering ratio and attenuation coefficients at the same area. Surprisingly, the colloidal-type subpopulations, which have often been operationally classified as "dissolved" and neglected for their scattering, exhibit significant backscattering with contributions of up to 40percent over the entire backward angles.
机译：对于具有已知大小，组成，结构和形状分布的粒子种群，可以通过控制关系从第一性原理（第一类Fredholm线性积分方程）估算其体积散射函数（VSF）。逆转弗雷德霍姆方程式以从测量的VSF导出粒子的组成和尺寸分布仍然具有挑战性，因为1）解决方案取决于核函数，以及2）需要构造核函数以避免奇异性。在这项研究中，提供了对早期和当前反演技术的全面回顾。提出了一种基于非负最小二乘的反演方法，并使用了由原型体积散射仪在新泽西州海岸外LEO-15站点测量的VSF进行评估。内核功能由单个子种群的汇编建立，每个子种群遵循对数正态分布，其特征尺寸和折射率完全覆盖了该地区潜在海洋颗粒的自然变化的整个范围。进行了敏感性分析，以确保所构建的内核功能既不是奇异的也不是病理性的。总共确定了126个潜在的亚群，其中11个在一半以上的倒置中很常见，并且只有五个始终存在（> 90％的测量值）。这五个亚群可解释为大小约为0.02μm的小胶体型颗粒，亚微米碎屑型颗粒（n_（r）velence 1.02，r_（mode）velence0.2μm），两个微米大小的亚种群一个相对柔和（n_（r）velence 1.04和r_（mode）velence 1.6μm），另一个相对折射（n_（r）velence 1.10和r_（mode）velence 3.2μm）和气泡具有相对大的尺寸（n_（r）velence 0.75和r_（mode）velence10μm）。重构的PSD具有双峰形状，较小的峰由胶体亚群控制，较大的颗粒由幂律函数近似。 Junge型坡度的平均值为-4.0 +-0.2，与全球海洋中的平均值-4.0密切相关。折射率的分布表明较高水分含量的颗粒占优势，这也与基于相同区域的反向散射比和衰减系数的早期结果一致。出乎意料的是，胶体类型的亚群在操作上经常被归类为“溶解的”并且由于其散射而被忽略，它们表现出显着的反向散射，在整个后向角上的贡献高达40％。

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