Metrics and standards for acoustic environmental assessments

Abstract

Because of stringent legal requirements and growing public interest, researchers must win government approval for any sea test involving acoustic emissions which could injure or harass marine animals. The approval process requires extensive documentation on the animals in the test area and likely impact of the test. This documentation (Environmental Assessment or Environmental Impact Statement) then includes predictions of shock wave and acoustic field characteristics in terms relevant to animal harassment and injury metrics. At present, there is no ‘‘standard’’ approach to developing an EA or an EIS; each research program provides its own format, metrics, etc. This presentation considers issues of standardization for the EA and EIS processes. In particular, literature on animal effects provides a variety of empirical thresholds in various units (e.g., peak pressure, impulse), while source metrics have their own particular units (e.g., energy density at range, intensity). Finally, signal must be estimated with a model that correctly propagates the quantity of interest in complex environments. None of these steps has a standard approach. Examples are given of problems encountered and recommendations made for standardization. Special attention is given to measurement techniques for marine animal response to sound.