Combining multibeam-sonar and multifrequency-echosounder data: examples of the analysis and imaging of large euphausiid schools

Abstract

Korneliussen, R. J., Heggelund, Y., Eliassen, I. K., Øye, O. K., Knutsen, T., and Dalen, J. 2009. Combining multibeam-sonar and multifrequency-echosounder data: examples of the analysis and imaging of large euphausiid schools. – ICES Journal of Marine Science, 66: 991–997. The first high-resolution, quantitative, multibeam sonar (Simrad MS70) ever developed was mounted in a keel of RV “G. O. Sars” with port-orientated beams. Each ping samples a volume of 60° horizontally × 45° vertically with 500 beams, which is often enough to insonify a complete school of fish or zooplankton. The large amount of resulting data is efficiently preprocessed with automatic, real-time detections of school candidates; these are accepted or rejected during post-processing. The system was used on the continental shelf near the Subantarctic island of South Georgia to study Antarctic krill (Euphausia superba), and some of the detected schools were immediately sampled with a six-frequency echosounder (Simrad EK60), then trawled with various nets to verify the target species and their size composition. For schools acoustically categorized as euphausiids, data from the two acoustic systems were used to estimate the school morphometrics and the krill size distributions. The principal objectives of this study were to explore the potential of combining data from a multibeam sonar, multifrequency echosounders, and nets, and to describe the efficient processing methods and software that facilitate the multi-instrument analyses. Three-dimensional morphometrics based on the MS70 data were consistent with corresponding two-dimensional morphometrics based on the echosounder data and could be used to improve the acoustic classifications of taxa or species. Additionally, automatic preprocessing and integration of data from different sources into the same user interface allowed efficient exploration and interpretation of all the acoustic data.

Section and Total Scattering Strengths of Individual Fish Schools

“…22,30,31) 25) cross-fan beam sonar, 23,24) and omnidirectional sonar, 22) which can scan vertical planes, should be used for this purpose. Since many research vessels install a quantitative echo sounder and such a sonar, 22,32) can use the several beams oriented downward to measure SV vertically and vertical scan to obtain the 3D distribution of fish, so that only by such sonar the proposed method is realizable.…”

Diel Vertical Migration Behaviour of the Northern Krill (Meganyctiphanes norvegica Sars)

“…Baumgartner and Fratantoni, 2008;Davis et al, 2008), and have provided new information on Antarctic krill (Brierley et al, 2002). Multibeam sonars have recently been exploited for characterising Antarctic krill school structure (Korneliussen et al, 2009). Even the use of low frequency acoustics to characterise distribution of Antarctic krill at the mesoscale level has been suggested ( Jagannathan et al, 2009), but Antarctic krill represents a special case of a dominant, schooling species which does not strictly apply to M. norvegica.…”

Simulations of multi-beam sonar echos from schooling individual fish in a quiet environment

“…It outputs simulated data for the specified instrument. The model facilitates the interpretation of real multi-beam data in terms of individual fish behaviors 32 and their aggregation morphology 33,34 and dynamics. 35 Furthermore, hypotheses regarding the spatiotemporal and orientational distributions of the targets 36 comprising a school, and their aggregate behavior, can be translated by the model to simulated acoustic observations for comparisons to real data.…”