Super-resolution data assimilation

TL;DR

This paper introduces Super-resolution data assimilation (SRDA), a neural network-based method that enhances low-resolution model forecasts to high-resolution accuracy, significantly improving data assimilation performance with manageable computational costs.

Contribution

The study presents a novel SRDA approach that uses neural networks to emulate high-resolution fields from low-resolution forecasts, outperforming traditional interpolation methods in data assimilation.

Findings

SRDA reduces errors by 40% compared to low-resolution assimilation.

SRDA's performance is close to high-resolution systems, with only 16% larger errors.

Computational cost increases by 55%, but accuracy gains are substantial.

Abstract

Increasing the resolution of a model can improve the performance of a data assimilation system: first because model field are in better agreement with high resolution observations, then the corrections are better sustained and, with ensemble data assimilation, the forecast error covariances are improved. However, resolution increase is associated with a cubical increase of the computational costs. Here we are testing an approach inspired from images super-resolution techniques and called "Super-resolution data assimilation" (SRDA). Starting from a low-resolution forecast, a neural network (NN) emulates a high-resolution field that is then used to assimilate high-resolution observations. We apply the SRDA to a quasi-geostrophic model representing simplified surface ocean dynamics, with a model resolution up to four times lower than the reference high-resolution and we use the Ensemble Kalman Filter data assimilation method. We show that SRDA outperforms the low-resolution data assimilation approach and a SRDA version with cubic spline interpolation instead of NN. The NN's ability to anticipate the systematic differences between low and high resolution model dynamics explains the enhanced performance, for example by correcting the difference of propagation speed of eddies. Increasing the computational cost by 55\% above the LR data assimilation system (using a 25-members ensemble), the SRDA reduces the errors by 40\% making the performance very close to the HR system (16\% larger, compared to 92\% larger for the LR EnKF). The reliability of the ensemble system is not degraded by SRDA.