Fig. 3. Flow noise increases with flow speed. The tag was attached to a wing and towed at different speeds in order to establish a relationship between flow noise magnitude and flow velocity. Flow noise was determined by calculating the root-mean-square sound pressure at the 50-Hz 1/3 octave bands. The 50-Hz 1/3 octave band was chosen because it exhibited both a high flow noise level and a distinct partitioning of flow noise magnitude for each flow velocity. The least-squares regression through the data is described by the equation y=0.0015x²–0.3327x+18.748; r²=0.99. This equation was used to estimate the instantaneous speed of the whale throughout the dive cycle for a given level of flow noise recorded by the tag.