Assessing uncertainties in scattering correction algorithms for reflective tube absorption measurements made with a WET Labs ac-9

Nicole D. Stockley, Rüdiger Röttgers, David McKee, Ina Lefering, James M. Sullivan, Michael S. Twardowski

Research output: Contribution to journalArticle

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Abstract

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 nearinfrared (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.
LanguageEnglish
PagesA1139-A1153
Number of pages15
JournalOptics Express
Volume25
Issue number24
DOIs
StatePublished - 10 Nov 2017

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scattering functions
tubes
scattering
subtraction
water
oceans
stations

Keywords

  • remote sensing
  • sensors
  • absorption
  • oceanic optics
  • optical sensing

Cite this

Stockley, Nicole D. ; Röttgers, Rüdiger ; McKee, David ; Lefering, Ina ; Sullivan, James M. ; Twardowski, Michael S./ Assessing uncertainties in scattering correction algorithms for reflective tube absorption measurements made with a WET Labs ac-9. In: Optics Express. 2017 ; Vol. 25, No. 24. pp. A1139-A1153
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abstract = "In situ absorption measurements collected with a WET Labs ac-9 employing areflective 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 nearinfrared (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.",
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Assessing uncertainties in scattering correction algorithms for reflective tube absorption measurements made with a WET Labs ac-9. / Stockley, Nicole D.; Röttgers, Rüdiger; McKee, David; Lefering, Ina; Sullivan, James M.; Twardowski, Michael S.

In: Optics Express, Vol. 25, No. 24, 10.11.2017, p. A1139-A1153.

Research output: Contribution to journalArticle

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N2 - In situ absorption measurements collected with a WET Labs ac-9 employing areflective 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 nearinfrared (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.

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