FIGURE 13. Boat-wakes in Three-Mile Slough (sampling rate 3 per second): (a) Unfiltered data, with positions indicated when passing boats were observed visually--note that the boat wake is practically invisible before filtering; (b) Filtered data; (c) Wavelet coefficients--the lower four scales have been multiplied by 20 to make them more visible. The filtering consists of zeroing all coefficients except the two highest-frequency scales.