Long-term continuous monitoring of the diffuse attenuation coefficient at 490 nm from global oceans using combined SeaWiFS and MODISA data

ABSTRACT

To enhance the long-term monitoring ability of multi-sourced remote sensing data, we needed to minimize the inter-mission biases between the data retrieved from different satellites. We evaluated three existing diffuse attenuation coefficients at 490 nm (K_d(490)) using nine independent datasets collected from the global oceans. The results indicate that the updated neural network-based four-band K_d(490) retrieval model (updated-NFKM) decreased the uncertainty by > 4% from the NASA official K_d(490) retrieval model (NOKM) and the inherent optical properties-based K_d(490) retrieval model (IOPK). Specifically, matchup analysis showed that the updated-NFKM model produced < 40% uncertainty in deriving K_d(490) from MODISA and SeaWiFS data, and the uncertainty of SeaWiFS-predicted K_d(490) was ~ 5% lower than the MODISA-predicted K_d(490). Using the updated-NFKM model, >80% of the global ocean had an uncertainty for K_d(490) estimates that were lower than 30%, while the model performed much better for the Western Pacific, Arctic Ocean, and Northern Atlantic compared to the Eastern Pacific, South Ocean, and Southern Atlantic. To enable a naturally smooth transition from SeaWiFS to MODISA-observed K_d(490) products, it was critical to cross-calibrate the inter-mission difference. The results show that using the cross-calibration models proposed in this study, the MODISA-predicted K_d(490) accounted for > 86% of the variations of SeaWiFS-predicted K_d(490), even though the empirical coefficients of the cross-calibration model had to be adjusted according to the time scales of the composite remote sensing data. Finally, we used the cross-calibration model to minimize the time series of SeaWiFS and MODISA-predicted K_d(490) data. Our results indicate that the K_d(490) values gradually increased in the low-latitude regions during past two decades.

KEYWORDS:

• Heat stratification
• upper oceanic layer
• turbid water
• solar heating
• integrated attenuation coefficient model

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The National Natural Science Foundation of China [42022045, Chen], and Shan’xi Key Research and Development Program [2022ZDLSF06-09, Chen] provided financial support for this study.