9 Jan 2026

Review of Hydroacoustic Data Associated with Small-Diameter Vinyl and Timber Pile Driving Operations

This review investigates root-mean-square sound levels, peak sound levels, and single-strike sound exposure levels resulting from small-diameter vinyl and timber pile driving operations with sufficient supporting information to assess potential impact on endangered species identified in the NOAA acoustic impact calculator. We identify 49 relevant records associated with installing timber pilings 14 in. in diameter and smaller and one record associated with vinyl piling. While acceptable for use as proxy data within the NOAA tool, the records exhibit significant unexplainable scatter of as much as +20 dB. Example calculations show that well intentioned hypothetical proposals coordinated in the permit application process could project vastly different impacts to endangered species. We therefore conclude that, within the framework of current practices and tools, these data cannot support informed decision-making by US Army Corps of Engineers (USACE) regulators as to whether small-scale timber or vinyl pile driving operations will jeopardize the continued existence of protected species or result in the destruction or adverse modification of critical habitat to comply with the Endangered Species Act. We recommend supplementing existing data with targeted collections as well as developing pile-specific coordination and assessment guidance for use by USACE regulators during the permitting process.

12 Aug 2025

Acoustic Winter Terrain Classification for Offroad Autonomous Vehicles

Abstract: Autonomous vehicles can experience extreme changes in performance when operating over winter surfaces, and require accurate classification to transit them safely. In this work we consider acoustic classification of winter terrain, and demonstrate that a simple and efficient frequency-space analysis exposed to a small convolutional neural network, rather than recurrent architectures or temporally-varying spectrogram inputs, is sufficient to provide near-perfect classification of deep snow, hardpacked surfaces and ice. Using a dual-microphone configuration, we also show that acoustic classification performance is due to a combination of vehicle noises and vehicle-terrain interaction noises, and that engine sounds can serve as a particularly powerful classification cue for offroad environments.

2 Nov 2022

Willis Coupling in One-dimensional Layered Bulk Media

Abstract: Willis coupling, which couples the constitutive equations of an acoustical material, has been applied to acoustic metasurfaces with promising results. However, less is understood about Willis coupling in bulk media. In this paper a multiple-scales homogenization method is used to analyze the source and interpretation of Willis coupling in one-dimensional bulk media without any hidden degrees of freedom, or one-dimensional layered media. As expected from previous work, Willis coupling is shown to arise from geometric asymmetries, but is further shown to depend greatly on the measurement position. In addition, a discussion of the predicted material properties, including Willis coupling, of macroscopically inhomogeneous media is presented.

13 Oct 2022

Data Acquisition Software for Impedance Tube Measurements

Abstract: Transmission impedance tube measurements are necessary to measure the asymmetric acoustic property known as Willis coupling. However, software is required to measure and store data from an impedance tube for acoustic material characterization. This report details the overall structure of custom-developed software built from low-level functions. Software libraries from the data acquisition system as well as the HDF5 file system are the basis for the code. A command line user interface guides a user through the necessary steps in data collection.

29 Jan 2021

Optical and Acoustical Measurement of Ballistic Noise Signatures

Abstract: Supersonic projectiles in air generate acoustical signatures that are fundamentally related to the projectile’s shape, size, and velocity. These characteristics influence various mechanisms involved in the generation, propagation, decay, and coalescence of acoustic waves. To understand the relationships between projectile shape, size, velocity, and the physical mechanisms involved, an experimental effort captured the acoustic field produced by a range of supersonic projectiles using both conventional pressure sensors and a schlieren imaging system. The results of this ongoing project will elucidate those fundamental mechanisms, enabling more sophisticated tools for detection, classification, localization, and tracking. This paper details the experimental setup, data collection, and preliminary analysis of a series of ballistic projectiles, both idealized and currently in use by the U.S. Military.