Functional-prior-based approaches to Bayesian PDE-constrained inversion using physics-informed neural networks

TL;DR

This paper introduces functional-prior-based methods for Bayesian PDE inversion using physics-informed neural networks, enabling the incorporation of physically meaningful priors in function space.

Contribution

It proposes two novel approaches, FPI-BPINN and fParVI-PINN, to integrate functional priors into Bayesian PINN-based inverse problems.

Findings

Both methods accurately estimated posterior distributions in experiments.

Random Fourier features improved Gaussian prior representation and posterior approximation.

FPI-BPINN offers flexibility, while fParVI-PINN provides higher accuracy.

Abstract

Physics-informed neural networks (PINNs) provide a mesh-free framework for solving PDE-constrained inverse problems, but their extension to Bayesian inversion still faces a fundamental difficulty: prior distributions are typically defined in the weight space of neural networks, whereas physically meaningful prior assumptions are more naturally expressed in function space. In this study, we introduce a unified framework, termed functional-prior-based approaches to Bayesian PDE-constrained inversion using physics-informed neural networks (fpBPINN), to incorporate functional priors into Bayesian PINN-based inversion. We consider two complementary approaches. The first is a functional-prior-informed Bayesian PINN (FPI-BPINN), in which a neural network weight prior is learned to be consistent with a prescribed functional prior, and Bayesian inference is subsequently performed in weight space. The second is function-space particle-based variational inference for PINNs (fParVI-PINN), which performs Bayesian estimation using ParVI directly in function space. We also show that random Fourier features (RFF) play an important role in representing Gaussian functional priors with neural networks and in improving posterior approximation. We applied the proposed approaches to one-dimensional seismic traveltime tomography and two-dimensional Darcy-flow permeability inversion. These numerical experiments showed that both approaches accurately estimated posterior distributions, highlighting the significance of introducing physically interpretable functional priors into Bayesian PINN-based inverse problems. We also identified the contrasting advantages of FPI-BPINN and fParVI-PINN, namely flexibility and accuracy, respectively.