Measurement uncertainties in PSICAM and reflective tube absorption meters

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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 (https://doi.org/10.1364/OE.26.024384)

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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
    Subjects:Science > Physics
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:03 Sep 2018 13:41
    Last modified:12 Dec 2024 07:03
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/65344
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