Operation and use of the Simrad EK500 on NBP02-04

Scott Gallager, Alec Scott, Philip Alatalo, and Dicky Allison

Data for the entire cruise were collected from all three frequencies on the Simrad EK500 from the 200 mile limit on day 215 through day 258. We addressed issues related to data collection, processing, calibration, and ice noise. Data from the Simrad EK500 are being processed and made available through the GLOBEC web site to augment data from BIOMAPER II and MOCNESS. An additional objective of this effort was to observe the association of acoustic backscatter with thermal gradients measured with the CTD and the CMIPS high resolution turbulence probe. At stations where the CTD/CMIPS was deployed and the Simrad EK500 data are available, correspondence between the acoustic record and turbulence structure may be made. Temperature profiles and the first order gradient in temperature are associated with acoustic backscatter intensity. Mid water column shear instability was imaged under so-called well-mixed conditions providing evidence of particle accumulation in regions of high shear. Examples will be shown where backscatter was likely due to turbulence and where it was likely due to scattering off of plankton and particles.