Spectral Holography: Imaging Complex Systems with Broadband Sound

Conventional holograms record the structure of scattered waves at many spatial positions, but just one frequency. These recordings encode information about the positions, sizes and material properties of the scatterers that can be extracted either by numerically reconstructing the three-dimensional wave or by analyzing the hologram with a generative model as an inverse problem. Much of the same information can be captured in the frequency dependence of the amplitude and phase of scattered waves recorded at a very small number of positions. While such spectral recording would be challenging in optical holography, it is a natural fit for acoustic holography. We introduce spectral holography by demonstrating Lorenz-Mie tracking and characterization of macroscopic objects with broadband sound.