Measurement uncertainties in PSICAM and reflective tube absorption meters

Lefering, Ina and Röttgers, Rüdiger and Utschig, Christian and Twardowski, Michael S. and McKee, David (2018) Measurement uncertainties in PSICAM and reflective tube absorption meters. Optics Express, 26 (19). pp. 24384-24402. ISSN 1094-4087

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    Abstract

    The nature and magnitude of measurement uncertainties (precision and accuracy) associated with two approaches for measuring absorption by turbid waters are investigated here: (a) point source integrating cavity absorption meters (PSICAM), and (b) reflective tube absorption meters (AC-9 and AC-s – both WET Labs Inc., USA). Absolute measurement precision at 440 nm was quantified using standard deviations of triplicate measurements for the PSICAM and de-trended, bin averaged time series for the AC-9/s, giving comparable levels (< 0.006 m-1) for both instruments. Using data collected from a wide range of UK coastal waters, PSICAM accuracy was assessed by comparing both total non-water absorption and absorption by coloured dissolved organic material (CDOM) measured on discrete samples by two independent PSICAMs. AC-9/s performance was tested by comparing total non-water absorption measured in situ by an AC-9 and an AC-s mounted on the same frame. Results showed that the PSICAM outperforms AC-9/s instruments with regards to accuracy, with average spread in the PSICAM total absorption data of 0.006 m-1 (RMSE) compared to 0.028 m-1 for the AC-9/s devices. Despite application of a state of the art scattering correction method, the AC-9/s instruments still tend to overestimate absorption compared to PSICAM data by on average 0.014 m-1 RMSE (AC-s) and 0.043 m-1 RMSE (AC-9). This remaining discrepancy can be largely attributed to residual limitations in the correction of AC-9/s data for scattering effects and limitations in the quality of AC-9/s calibration measurements.

    ORCID iDs

    Lefering, Ina ORCID logoORCID: https://orcid.org/0000-0003-1167-2227, Röttgers, Rüdiger, Utschig, Christian, Twardowski, Michael S. and McKee, David ORCID logoORCID: https://orcid.org/0000-0001-8023-5923;
    • Item type:Article
      ID code:65344
      Dates:
      Date
      Event
      17 September 2018
      Published
      4 September 2018
      Published Online
      24 August 2018
      Accepted
      Keywords:measurement uncertainties, absorption, point source integrating cavity absorption meters (PSICAM), reflective tube absorption meters, Physics, Atomic and Molecular Physics, and Optics
      Subjects:Science > Physics
      Department:Faculty of Science > Physics
      Depositing user: Pure Administrator
      Date deposited:03 Sep 2018 13:41
      Last modified:30 Nov 2021 01:56
      Related URLs:
      URI:https://strathprints.strath.ac.uk/id/eprint/65344
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