AUTHOR=Chen Zhihui , Wang Pinqiang , Bao Senliang , Zhang Weimin 

TITLE=Rapid reconstruction of temperature and salinity fields based on machine learning and the assimilation application

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 9 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.985048

DOI=10.3389/fmars.2022.985048

ISSN=2296-7745

ABSTRACT=Satellite observations play important roles in ocean operational forecasting systems, however, the direct assimilation of satellite observations cannot provide sufficient constraints on the model underwater structure. This study adopted the indirect assimilation method. First, we created a 3D temperature and salinity reconstruction model that took into account the advantage of the nonlinear regression of the generalized regression neural network with the fruit fly optimization (abbreviated as FOAGRNN). Compared with the SODA3.4.2 reanalysis product and the WOA13 climatology data, the reconstructed T/S profiles had better accuracy and could better describe the characteristics of mesoscale eddies and the thermocline structure. Then, the reconstructed T/S profiles were assimilated into the Regional Ocean Model System (ROMS) using the Incremental Strong constraint 4D Variational (I4D-Var) data assimilation algorithm. The quantitative and qualitative analysis results indicated that compared with the direct assimilation of satellite observations, the root mean square errors (RMSEs) of temperature and salinity were reduced by 34% and 31% respectively by assimilating the reconstructed T/S profiles. Furthermore, this method significantly improved the simulation effect of the model underwater structure, especially in the 300 m to 500 m water layer. Compared with the National Information Center’s real-time analysis data, the machine learning-based assimilation system demonstrated a significant advantage in the simulation of underwater salinity structure with an RMSE reduced by 12.5%, while showing a similar performance in the simulation of underwater temperature structure.