HR: 0800h
AN: OS51C-02    [Abstracts]
TI: The use of ADCPs for Detecting Turbulence
AU: * Fransson, L O
EM: lindaf@misu.su.se
AF: Department of Meteorology/Physical Oceanography, Stockholm University 106 91 Stockholm Sweden, Stockholm, 106 91, Sweden
AB: It is generally assumed that the backscatter utilized by Acoustic Doppler Current Profilers (ADCPs) originates from particulate or biological matter in the water column. Based on a 70-day data set from the deeper reaches of the Faroe-Bank Channel, it is, however, demonstrated that under pronounced shear-flow conditions turbulence- induced density inhomogeneities appear to be capable of also serving this purpose. Measurements took place at three different stations representing varying hydrographic situations; across the channel the density stratification associated with the shear zone increases significantly between the northeastern side and the southwestern side. The recorded magnitude of the acoustic-return intensity proved to be highest at the level of maximum vertical shear. A large number of data losses were furthermore found in the shear layer, most likely due to the fish- rejection option included in the signal processing. A closer investigation showed a correlation between the data losses and the predominant semi-diurnal tide which supports the hypothesis that the high return signals are due to turbulence-induced density inhomogeneities; it is unlikely that particulate/biological matter suspended in the free water mass would show any tidal dependence. This suggested use of ADCPs is based of the same principles as those underlying Sonic Detection and Ranging (SODAR) used in atmospheric research.
DE: 4259 Ocean acoustics
DE: 4262 Ocean observing systems
DE: 4294 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly