## 5 Conclusions
We further validated both QCs against satellite SSTs from available data sets of matchups for September 1981-December 2021 from several ACSPC RANs, including AVHRR GAC RAN2 from NOAA-07/09/11/12/14/15/16/17/18/19; AVHRR FRAC RAN1 from MetopA/B/C; VIIRS RAN3 from S-NPP/NOAA-20; and MODIS RAN1 from Terra/Aqua. The simultaneous use of matchups from satellites flying in different orbits allows for validating the diurnal signals observed in in situ SSTs, as well as discriminating the'real' diurnal variations in the water temperature from 'false' diurnal signals caused by the extraneous factors. Compared with the current iQuam QC, the DRC better preserves true diurnal variations in in situ SST, as well as its deviations from reference SST in the dynamic zones. At the same time, it efficiently rejects unrealistically large deviations from the reference SST. As a result, the DRC minimizes suppression of spatial and temporal variability in in situ SST and reduces the dependency of the QC results on the specific L4 analysis. In particular, the DRC reconciles the estimates of the mean global diurnal cycle derived from deviations of in situ SST from different L4 analyses, and increases their amplitudes. Overall, the DRC increases the monthly numbers of quality in situ SST measurements by 4-6% and improves the correlation between deviations of satellite and in situ SSTs from reference SST at the expense of increased SDs of deviations of in situ from satellite SST. We also explored the potential of introducing the additional, satellite-based quality level for in situ SSTs based on matching them with satellite SSTs. The exclusion of ~1% of outliers from the matchups reduces the standard deviations of in situ SSTs minus satellite SSTs below the levels typical for the current iQuam QC and significantly increases the correlation between \(T_{IS}-T_{L4}\) and \(T_{SAT}-T_{L4}\). The fraction of in situ measurements to which this new QL can be assigned, is relatively small in the earlier years, ranging from ~2.6% in the 1980s and increasing to 18-25% in the 2010s. However, these are the very same matchups used in Cal/Val of satellite retrievals. It is expected, therefore, that the elimination of these outliers will improve the satellite Cal/Val. Work is underway to implement the DRC in the official future releases of the iQuam. Future work will also aim at the development of advanced QC procedures for the platforms with a relatively low temporal sampling rate (ships, Argo floats), evaluation of the effects of the new QC on the training and validation of satellite SST retrievals, and further refining the DRC parameters as needed. Conceptualization, B.P. and A.I. ; methodology, B.P. ; software, B.P. ; validation, B.P., V.P. and O.J. ; formal analysis, B.P. ; investigation, B.P., A.I. and V.P. ; resources, A.I. ; data curation, V.P. and O.J. ; writing--original draft preparation, B.P. ; writing--review and editing, A.I. and BP. ; visualization, B.P. and V.P. ; supervision, A.I. ; project administration, A.I. ; funding acquisition, A.I. All authors have read and agreed to the published version of the manuscript. This work was supported by the following NOAA Programs: JPSS ([PERSON], JPSS Manager; [PERSON], JPSS Program Scientist; [PERSON], JSTAR Manager), GOES-R ([PERSON], Chair, Algorithm Working Group), ORS ([PERSON] and [PERSON], Managers), and NESDIS Innovation ([PERSON], NESDIS Chief Scientist and Program Manager). **Informed Consent Statement:** Not applicable. **Data Availability Statement:** In situ data processed with the current iQuam v.2.10 are available at [[https://www.star.nesdis.noaa.gov/socd/sst/iquam/](https://www.star.nesdis.noaa.gov/socd/sst/iquam/)]([https://www.star.nesdis.noaa.gov/socd/sst/iquam/](https://www.star.nesdis.noaa.gov/socd/sst/iquam/)) (accessed on 3 September 2023). In situ data reprocessed with the modified iQuam will be available after updating the official iQuam version. **Acknowledgments:** We thank NOAA JPSS, GOES-R, ORS, and NESDIS Innovation Programs for sustained support of _i_Quan development.