Fig. 8
From: Sounding out life in the deep using acoustic data from ships of opportunity
Importance of transducer motion correction. (a) Checking the precondition of Dunford68 algorithm using PSD analyses of motion data recorded by selected vessels with varying dimensions and range of weather conditions, indicating the strength of variations (energy) in pitch and roll data as a function of waveform frequency. Recorded pitch and roll data were converted from Cartesian to polar coordinate for translating platform motion as transducer angle off-axis. (b) Shows spectrogram analysis of example motion data recorded by RV Investigator at a sampling rate of 10 Hz, indicating temporal variations in waveform frequencies with insignificant energy contribution from rapid vessel movements above 2 Hz. Panels (c,d) display magnitudes and effects of transducer motion correction (see Table 7 for description) applied to 18 and 38 kHz calibrated raw \({s}_{v}\) data recorded onboard RV Investigator during 12–13 March 2018 in Southern Ocean, highlighting expected changes between beamwidths of transducers used. Similarly, (e) the magnitudes of motion correction applied to 38 kHz calibrated raw \({s}_{v}\) data recorded onboard FV Isla Eden during 06–16 June 2019 in Southern Indian Ocean is provided to highlight appreciable changes between vessel design and nature of sea state. Note the non-linear range dependent effect in all cases. In boxplots, the vertical line inside of each box is the sample median. The right and left edges of each box are the upper and lower quartiles respectively. The distance between the right and left edges is the interquartile range (IQR). Values that are more than 1.5 IQR away from the right or left of the box are outliers (red plus sign).
