The imaginary part of the scattering Green function: monochromatic relations to the real part and uniqueness results for inverse problems

TL;DR

This paper establishes new algebraic identities relating the real and imaginary parts of the Green function for wave equations, leading to local uniqueness results in inverse problems with single and multiple frequencies.

Contribution

It introduces novel algebraic identities between Green function components, enabling local uniqueness proofs for inverse wave problems with limited frequency data.

Findings

Proves local uniqueness for Schrödinger equation with one frequency.

Establishes local uniqueness for acoustic wave equation with two frequencies.

Develops new algebraic identities involving Green function components.

Abstract

For many wave propagation problems with random sources it has been demonstrated that cross correlations of wave fields are proportional to the imaginary part of the Green function of the underlying wave equation. This leads to the inverse problem to recover coefficients of a wave equation from the imaginary part of the Green function on some measurement manifold. In this paper we prove, in particular, local uniqueness results for the Schr{\"o}dinger equation with one frequency and for the acoustic wave equation with unknown density and sound speed and two frequencies. As the main tool of our analysis, we establish new algebraic identities between the real and the imaginary part of Green's function, which in contrast to the well-known Kramers-Kronig relations involve only one frequency.