Abstract
Abstract Today, numerous scientific echosounders are used as continuously monitoring systems in ocean observatories. These echosounders are usually calibrated in shallow water, either in laboratory tanks or at random ocean docks before deployments. If the systems are used for quantitative measurements by the observatories, they should be calibrated at the operating depths to consider the environmental effects on the calibration parameters. In this article, a simple in situ calibration method is presented, which was recently applied to one of the nodes of the Norwegian Lofoten-Vesterålen ocean observatory, when the research vessel with dynamic positioning system suspended and moved the calibration sphere between the vessel and the transducer. The calibration results of a 70-kHz split-beam echosounder demonstrate that this method can be applied to the cabled observatories.
Highlights
Ocean observatories provide data of multiple oceanic variables for scientific researches (Favali and Beranzoli, 2006), and interests for real time data acquisitions have been realized by cabled ocean observatories that assist monitoring rapid changes, as well as long-term observations
Compared to a standard vessel calibration with the target at about 20 m, the variability increases with the pulse volume at 180 m range, in which reverberating targets were inside the pulse volume and some fish targets were observed between the transducer and the calibration sphere
It is known that these factors will increase the phase variability and the variance of the calibration results
Summary
Ocean observatories provide data of multiple oceanic variables for scientific researches (Favali and Beranzoli, 2006), and interests for real time data acquisitions have been realized by cabled ocean observatories that assist monitoring rapid changes, as well as long-term observations. Compared to a standard vessel calibration with the target at about 20 m, the variability increases with the pulse volume at 180 m range, in which reverberating targets (zooplankton) were inside the pulse volume and some fish targets were observed between the transducer and the calibration sphere.
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