Assessing uncertainties in scattering correction algorithms for reflective tube absorption measurements made with a WET Labs ac-9.
Assessing uncertainties in scattering correction algorithms for reflective tube absorption measurements made with a WET Labs ac-9.
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评估使用 WET Labs ac-9 进行的反射管吸收测量的散射校正算法的不确定性。
作者：
N. Stockley;R. Röttgers;D. McKee;Ina Lefering;J. Sullivan;M. Twardowski
原位吸收测量收集与WET实验室ac-9采用反射管的方法进行散射校正使用几种可能的方法，并进行比较，由PSICAM的参考测量，以评估性能。总的来说，两种校正方法对采样站的效果最好：一种是使用ac-9和PSICAM之间的经验关系来推导近红外（NIR）中的散射误差（ε），另一种是从体积散射函数（VSF）的同时测量中独立推导出ε。基于VSF的方法的应用可能更普遍适用，尽管由于缺乏市售VSF仪器而难以常规应用。经验方法的性能是令人鼓舞的，因为它只依赖于交流表的测量，并可以很容易地应用到历史数据，虽然不可避免地有一些固有的假设颗粒组成，阻碍了普遍适用性。即使是性能最好的方法，对于许多水类型，通常也会观察到20%或更高的残留误差。对于清澈的海洋沃茨，假设近红外吸收可以忽略不计的传统基线减法的效果与上述方法一样好或更好，因为传播的不确定性低于比例方法观察到的不确定性。
In situ absorption measurements collected with a WET Labs ac-9 employing a reflective tube approach were scatter corrected using several possible methods and compared to reference measurements made by a PSICAM to assess performance. Overall, two correction methods performed best for the stations sampled: one using an empirical relationship between the ac-9 and PSICAM to derive the scattering error (ε) in the near-infrared (NIR), and one where ε was independently derived from concurrent measurements of the volume scattering function (VSF). Application of the VSF-based method may be more universally applicable, although difficult to routinely apply because of the lack of commercially available VSF instrumentation. The performance of the empirical approach is encouraging as it relies only on the ac meter measurement and may be readily applied to historical data, although there are inevitably some inherent assumptions about particle composition that hinder universal applicability. For even the best performing methods, residual errors of 20% or more were commonly observed for many water types. For clear ocean waters, a conventional baseline subtraction with the assumption of negligible near-IR absorption performed as well or better than the above methods because propagated uncertainties were lower than observed with the proportional method.