Inverted echosounder for continuous high-resolution water column profiling from the NEPTUNE (Canada) ocean observatory

In the fall of 2009 a 3-frequency (38, 123, and 210 kHz) upward-looking echo sounder was deployed in 95m of water at the inshore Folger Passage node of the NEPTUNE Canada observatory. NEPTUNE (North-East Pacific Time-Series Undersea Networked Experiments) is an 800 km cabled ocean observation system off the Pacific coast of Canada which is now online and operational. The system supplies DC power to permanently sited instruments, and supports a bi-directional high-bandwidth datastream using optical fibres. Echo sounding at the Folger node currently takes place at 1 Hz for all 3 frequencies, interleaved with pings from other acoustic equipment at the node. This data is returned in real-time to a shore station, and is then archived and accessed via a Data Management and Archiving System (DMAS). Preliminary investigations of the first 4 months of the datastream show a wealth of information about the temporal variation of fish, zooplankton, and bubbles, which are themselves related to fish behavior and surface conditions. Significant variations occur over scales from 10 minutes to seasonal. The NEPTUNE observatory is designed for a lifetime of 20 years, and the acoustic record should allow for the investigation of long-term changes in biological conditions on the west coast of Canada.