Learning Data-driven Surrogate and Correction Models for Satellite Observations in Numerical Weather Prediction

TL;DR

This paper develops machine learning-based surrogate models for satellite radiance observations in weather prediction, improving accuracy and efficiency by combining physics-based and data-driven approaches.

Contribution

It introduces two novel machine learning surrogate observation operators, including a hybrid residual correction model, for more accurate and computationally efficient satellite data assimilation.

Findings

Hybrid model reduces RMSE compared to RTTOV and fully data-driven emulator.

Both models incorporate 3D convolutions and U-Net architectures for spatial and vertical feature learning.

Hybrid residual model maintains physical consistency while enhancing radiance accuracy.

Abstract

Satellite observations play a critical role in numerical weather prediction where they are assimilated through an observation operator that maps model states to radiances. In the traditional Ensemble Kalman Filter, these observations are used to update the state by weighting their associated errors against model uncertainties to produce an optimal estimate. This process requires radiative transfer simulations for passive, downward-viewing satellite radiometers operating in the visible, infrared, and microwave spectra. Typically, such simulations rely on numerically integrating physical laws via models like RTTOV. In this paper, we introduce two machine learning surrogate observation operators inspired by modern computer-vision architectures: First, a fully data-driven emulator of radiative transfer, and second, a hybrid incremental correction model that learns only the residual relative to RTTOV, thereby retaining established physics while enabling data-driven refinement in complex conditions such as cloud-affected situations. The residual formulation improves radiance accuracy (lower Root Mean Squared Error (RMSE) than the fully data-driven emulator and RTTOV) and adds only moderate computational costs to the assimilation step. Both models combine 3D convolutions for vertical profile encoding with a 2D U-Net operating on latitude-longitude grids, allowing joint learning of vertical structure, spatial correlations, and inter-channel dependencies. We further provide a theoretical justification for deploying the hybrid surrogate as an observation operator in data assimilation.