Over the last century, over 16 million ocean temperature profiles have been acquired. However, each approach provides data with varying degrees of precision, quality, and metadata completion.
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The quality control (QC) process is required before using this raw data in scientific studies to assure data accuracy and availability. QC was earlier handled manually by experts. However, due to manpower and time constraints, manual QC of huge datasets is not practical.
Scientists from the Chinese Academy of Sciences’ (CAS) Institute of Atmospheric Physics (IAP) and their associates offer a novel climatological range-based automatic quality control system for ocean temperature in-situ profiles. This system is known as CAS Ocean Data Center–Quality Control system, or CODC–QC for short, and comprises 14 distinct quality checks to pinpoint outliers.
The research was published in the journal Deep-Sea Research Part I.
We developed this new QC system to provide a quality-homogenous database, with reduced human-workload and time cost on manual QC.
Zhetao Tan, Study First Author, Institute of Atmospheric Physics, Chinese Academy of Sciences
In CODC-QC, the 0.5% and 99.5% quantiles are used as thresholds to define local climatological ranges. These thresholds are time-varying, with the goal of incorrectly excluding real data during “extreme events.” These strategies are used in local climatological range checks for both temperature and vertical temperature gradient, where the anisotropic feature of water properties is attributed to, and topography barriers adjustment of water mass is made.
Furthermore, the CODC-QC system’s performance was evaluated using two expert/manual QC-ed benchmark datasets. This evaluation confirmed the effectiveness of the suggested strategy in deleting false data and reducing the percentage of valuable data incorrectly flagged.
The CODC-QC was also applied to the global World Ocean Database (WOD18), which included 16,804,361 temperature profiles spanning the years 1940 to 2021. According to temperature outlier statistics, 7.97% of measurements were rejected, with XBT data having the highest rejection rate (15.44%) and the Argo profiling float having the lowest rejection rate (2.39%).
We suggest a dependency of the quality of temperature observations on the instrumentation type.
Viktor Gouretski, Study Co-Author and Researcher, Institute of Atmospheric Physics, Chinese Academy of Sciences
The investigators also used the CODC-QC system to study global ocean warming.
We found that the application of the CODC-QC system leads to a 15% difference for linear trend of the global 0–2000 m ocean heat content changes within 1991–2021, compared with the application of WOD-QC (NOAA/NCEI), implying a non-negligible source of error in ocean heat content estimate.
Lijing Cheng, Study Corresponding Author and Professor, Institute of Atmospheric Physics, Chinese Academy of Sciences
The quality-controlled (by CODC-QC) and bias-corrected ocean in-situ profile data of CAS-Ocean Data Center, Global Ocean Science Database (CODC-GOSD) are now available freely.
Tan, Z., et al. (2023) A new automatic quality control system for ocean profile observations and impact on ocean warming estimate. Deep Sea Research Part I. doi.org/10.1016/j.dsr.2022.103961.