Topological acoustic sensing of ground stiffness: Presenting a potential means of sensing warming permafrost in a forest

The exploitation of sound as a remote sensing platform for environmental monitoring is a novel avenue for detecting changes in subsurface temperatures and properties in permafrost. We present a workflow for using the geometric phase of ground-supported acoustic waves (i.e., seismic waves) due to scattering by trees in a forest as a means of detecting global changes in permafrost stiffness. We work with a simulated environment composed of discrete masses and springs as a testbed for the vibrational response of a forest. For two different spatial distributions of trees, the geometric phase of ground-supported acoustic waves is numerically calculated using MATLAB to show how changes in ground stiffness, due e.g., to changes in subsurface temperature, affect changes in the phase. For acoustic waves with frequencies near the resonant frequencies of the trees the phase is shown to vary more drastically with ground stiffness. This topological acoustic workflow may present a new approach to characterizing changes in permafrost and provide early warning of thawing permafrost, which is vital to maintaining infrastructure and access to natural resources.