Since the samples from the ADCP and echosounder are already accurately synchronized with each other in the one instrument, processing the data afterwards also becomes much more efficient.
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As an added touch for user flexibility, the Signature100 records the raw “demodulated acoustic return” signal. “This gives users the ability to process the signal using different algorithms, and to pick out different information from the signal that maybe our processing doesn’t reveal,” Velasco says.
Providing information on the movement of marine life
As reported in the IEEE paper, sea trials of the Signature100 in the Mediterranean Sea have demonstrated the high performance of this novel instrument. Focusing on the echosounder performance, a 70 kHz pulse (one of the three frequencies available in the system) was able to provide information on the movement of marine life.
Acoustically, a single fish can look very similar to a school of plankton of the same volume. For users to determine whether they are looking at one fish or a mass of plankton, and assess how big the individuals are, it is important they calibrate their echosounder for absolute backscatter. For the purposes of this initial field test, the Signature100’s echosounder was not calibrated for absolute backscatter, but from the movement patterns seen in the echograms the team is confident they detected the migration of plankton up and down the water column. Nortek is currently developing a way for users to calibrate the echosounders to enhance the instrument’s identification potential.