Automated Quality Control of AERONET-OC L WN Data

• Published in: Journal of atmospheric and oceanic technology 2022-12, Vol.39 (12), p.1961
• Main Authors: Zibordi, Giuseppe, Davide D’Alimonte, Kajiyama, Tamito
• Format: Article
• Language: English
• Subjects: Acceptance; Accuracy; Aerosol Robotic Network; Atmospheric aerosols; Automatic control; Automation; Chlorophyll; Chlorophyll a; Coastal waters; Consistency tests; Data quality control; Measurement; Mesotrophic waters; Ocean color; Ocean colour; Procedures; Prototypes; Quality control; Radiance; Reference levels; Sensors; Spectra; Water types
• ISSN: 0739-0572; 1520-0426
• DOI: 10.1175/JTECH-D-22-0029.1

Quality control (QC) practices are a fundamental requirement for any measurement program targeting the delivery of high-quality data. In agreement with such a need, the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) includes a number of QC steps ensuring the delivery of normalized water-leaving radiance LWN spectra at incremental accuracy levels identified as level 1.0, level 1.5, and level 2.0. Currently, the final QC step allowing for rising level 1.5 LWN spectra to level 2.0 implies the execution of an expert-based procedure, which is extremely time consuming and naturally undergoes subjective decisions on dubious cases. These limitations solicited the development of an automated procedure, so-called A–QCLWN A–QCLWN, mimicking the steps supporting an expert analyst during the final QC of AERONET-OC LWN spectra. A–QCLWN A–QCLWNapplies hierarchical tests to check (i) the relative consistency of level 1.5 LWN spectra (called candidates) with respect to LWN reference spectra (called prototypes) constructed using LWN spectra formerly and independently quality controlled; (ii) the absence of any pronounced spectral feature in portions of each LWN candidate spectrum expected to exhibit a regular shape; and additionally, when applicable, (iii) the temporal consistency of the LWN candidate spectrum with respect to close-in-time spectra as a criterion to further strengthen the quality of data. A–QCLWN A–QCLWNperformance has been verified using LWN spectra from AERONET-OC measurement sites representative of various water types embracing oligotrophic/mesotrophic waters dominated by chlorophyll-a concentration and coastal waters exhibiting increasing levels of optical complexity. A–QCLWN A–QCLWNhas shown an acceptance rate of AERONET-OC level 1.5 LWN candidate spectra varying between approximately 89% and 93% with agreement in the range of 88%–93% with respect to the LWN spectra independently quality controlled through the expert-based procedure. The additional capability of A–QCLWN A–QCLWNto rank the fully quality-controlled LWN spectra combining weights depending on the various tests, anticipates the possibility to best support applications with diverse accuracy needs. Finally, acceptance rates of A–QCLWN A–QCLWNfor LWN prototype spectra built using level 1.5 data, an alternative to fully quality-controlled level 2.0, have shown values generally increased by less than 1%. This indicates the possibility to lessen the constraint implying the exist