An operational system for processing and visualizing multi-frequency acoustic data

Abstract

2002. An operational system for processing and visualizing multi-frequency acoustic data. -ICES Journal of Marine Science, 159: 293-313.Calibrated and digitized data from two or more discrete echosounder frequencies can be combined for the purpose of separating and extracting the acoustic scattering from zooplankton and fish in mixed recordings. This method is also useful for quantifying the relative contribution of each frequency to the total acoustic-backscattering when scrutinizing records in large-scale, acoustic surveys. Echosounder hardware requirements are defined which would permit the ideal extraction of such information. These include calibration, transducer specification, pulse resolution and digital representation of the signals. During this initial study a special version of the Simrad EK500 multi-frequency, split-beam echosounder and the Bergen Echo Integrator (BEI) post-processing system were used. The echosounder transmitted pulses simultaneously at four frequencies, 18, 38, 120 and 200 kHz and transferred the received signals to the post-processing system in calibrated, raw, digitized format. Methods are described for echogram manipulation and for the construction of new, synthetic, combinedfrequency [c(f)] echograms. Examples of extracted scattering information from mixed layers of fish and small scattering-organisms, such as copepods and euphausiids, are shown, and the potential of the method is discussed.

Sensor Fusion and Autonomy as a Powerful Combination for Biological Assessment in the Marine Environment

“…For example, in a mission south of Catalina Is., CA in September, 2013, there was an acoustic scattering layer at approximately 300 m. At the range this feature is sampled, the ship-based sensor had a horizontal footprint of 37-40 m while the AUV sensor, flying 4 m above the layer, had a footprint of 0.6-3.7 m. The increased resolution means one can now resolve individuals rather than simply the layer at these depths ( Figure 3). The multiple frequencies also allow for classification of the individuals into taxonomic categories and size estimates [30,31]. This system, therefore, makes it possible to examine the biology of animals in the mesopelagic zone in ways previously only possible in the upper ocean.…”

Prey selection of offshore killer whales Orcinus orca in the Northeast Atlantic in late summer: spatial associations with mackerel

“…Continuous data-recordings at 18, 38, 70, 120, and 200 kHz were made with a Simrad EK60 echo sounder from a transducer depth of 8 to 10 m underneath the surface down to 500 m depth, using standard acoustic settings (Korneliussen & Ona 2002) on board the MVs 'Libas' and 'Eros,' whereas 38 and 200 kHz were used onboard the MV 'Endre Dyrøy.' Acoustic data focusing on Norwegian spring spawning (NSS) herring from 2006 and 2007 were scrutinized by 2 experienced scientists with the software program Large Scale Survey System (Korneliussen et al 2009), and Nautical Area Scattering Coefficient (NASC) values enabled confident allocation to herring.…”

Section and Total Scattering Strengths of Individual Fish Schools

“…33) Therefore, the frequency response obtained by a multi-frequency echo sounder 21,34) , is theoretically reasonable.…”