Visualizing Zooplankton Distributions: Combined Video and Acoustic Mapping of Patch Structure.

Poster at AGU 1996.

Mark C. Benfield, Peter H. Wiebe, Charles H. Greene, Cabell S. Davis, Scott M. Gallager, Timothy K. Stanton

High-frequency acoustic surveys provide a means for rapidly quantifying the distribution of biological and non-living sound scatterers in the ocean. Recent advances in scientific visualization permit acoustic data collected from transects to be converted to a three-dimensional volume rendering of acoustic patchiness (Greene et al. 1994). Whil evisualizations of this type indicate substantial patchiness, single frequency acoustics cannot currently provide the identities of the scattering agents. The Video Plankton Recorder (VPR) is a towed system which provides data on the identities and size-frequencies of planktonic organisms and particulates along its tow path. The VPR provides a mechanism for verifying the identities of major sound scatterers. A joint-ship acoustic and VPR survey of a physically stratified region of Georges Bank revealed the presence of several large, subsurface acoustic patches. Associated VPR data suggests that these patches are predominantly generated by pteropods (Limacina), which are known to be extremely strong sound scatterers. The VPR and acoustics did not survey precisely the same water because they were towed by different vessels steaming parallel tracklines. This may explain some differences in the distribution of acoustic patches and volume-rendered VPR data. A new towed vehicle under construction (BIOMAPER II) will combine the VPR with multi-frequency acoustics on a single platform to provide a powerful tool for resolving the patch structure of marine zooplankton.