Clicks and recording

Click beam structure – small cetaceans The click beam is typically about 10o wide - measured out to half the 'on-axis' intensity. Lower frequency components spread more widely, and are less rapidly absorbed. There are side-lobes for each frequency. This creates a complex structure.

dolphin clicks show this at some frequencies

Side-lobes received by a C-POD as off-axis reflections - surface echoes: Colour shows frequency, height shows amplitude Direct path, beam centre Off beam axis, reflected by sea surface Beam centre, refracted path

'Multipath clusters' of echoes and refraction pathways are the norm for dolphin clicks and their similarity is useful evidence of a common source and pathway

.wav file record v C-POD-F record .wav file 500k/s click record 70 bytes 16 bytes Timing: 2microsecs C-POD-F timing resolution requires a starting sampling rate of 1MHz. Upsampled to 4MHz this gives accurate identification of some very useful waveform features - the position of the loudest cycle in a long click, and the cycle wavelength pattern around the peak. Click spectra often yield only 2 hard features (spectral peak and bandwidth), while high-res waveforms add several more. FFT spectrum bandwidth drops with click length. That is not useful, and a more stable measure can be derived from the high-res waveform.

Data volumes SAMBAH - Continuous .wav file records would require 12,000 TB or 4,000 TB with compression. Recording triggered by clicks could reduce the .wav file size further, but loses useful pathway information. SAMBAH - C-POD records - actual size 0.4 TB At present .wav file analysis is by eye, because automated error rates commonly exceed the maximum acceptable rate, and false positives can be in sporadic cluusters. So 1 day of data can take 8 hours to analyse by eye. SAMBAH had >100k days. SAMBAH automated analysis : 5 days.

… data analysis can be the killer!