The analysis of underwater acoustic data makes use of many descriptors and metrics. When data are carefully gathered, avoiding aliasing and clipping and including all necessary calibration and normalization factors it is possible to produce standard measures that agree with ISO standards. These descriptors allow precise comparisons to be made between data from different measurement campaigns using different equipment. Such precise comparisons are necessary if accurate estimates are to be made of any potential impact of sound on aquatic life. This report has set out definitions of metrics that can be used to describe signal amplitude, frequency-content, duration and energy, and their corresponding levels, where relevant. It has outlined procedures by which these metrics can be calculated, starting from an observable field quantity such as sound pressure, particle displacement, particle velocity or particle acceleration. Although the majority of underwater acoustic measurements available to date are of sound pressure, equal emphasis is given here on particle motion.

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