scholarly journals Variation of Zooplankton Mean Volume Backscattering Strength from Moored and Mobile ADCP Instruments for Diel Vertical Migration Observation

2019 ◽  
Vol 9 (9) ◽  
pp. 1851 ◽  
Author(s):  
Angga Dwinovantyo ◽  
Henry M. Manik ◽  
Tri Prartono ◽  
Susilohadi Susilohadi ◽  
Tohru Mukai
Keyword(s):  
Vertical Migration ◽  
Acoustic Doppler Current Profiler ◽  
Target Strength ◽  
Zooplankton Species ◽  
North Sulawesi ◽  
Lembeh Strait ◽  
Backscattering Strength ◽  
Current Profiler ◽  
The Mean ◽  
Sound Scattering Layer

Zooplankton can be detected by using acoustic Doppler current profiler (ADCP) instruments through acquiring the mean volume backscattering strength (MVBS) data. However, the precision of the backscattered signal measured by single ADCP measurement has a limitation in the MVBS variation of zooplankton. The objectives of this study were to analyze the MVBS and vertical velocity from ADCPs at the same time and location for zooplankton’s daily vertical migration (DVM) observation. Measurements were conducted in Lembeh Strait, North Sulawesi, Indonesia. Instruments used included a moored ADCP 750 kHz and a mobile ADCP 307.2 kHz. High MVBS value was found at 11.5–16 m depths and was identified as the sound scattering layer (SSL). The DVM patterns in the SSL displayed significant differences over time and had good relationships with the diurnal cycle. Theoretical target strength (TS) from the scattering models based on a distorted-wave Born approximation (DWBA) was estimated for Oithona sp. and Paracalanus sp.; the two dominant species found in the observed area. However, ΔMVBS and ΔTS proved that the dominant zooplankton species were not the main scatterers. The strong signal in SSL was instead caused by the schools of various zooplankton species.

scholarly journals Vertical structure of currents in the vicinity of the Iceland-Scotland Ridge

2005 ◽  
Vol 23 (6) ◽  
pp. 1963-1975 ◽  
Author(s):  
C. Carollo ◽  
I. Astin ◽  
J. Graff
Keyword(s):  
General Circulation ◽  
Bottom Topography ◽  
Acoustic Doppler Current Profiler ◽  
Tidal Currents ◽  
Residual Flow ◽  
Residual Currents ◽  
Tidal Motion ◽  
Dominant Component ◽  
Current Profiler ◽  
The Mean

Abstract. An analysis of current profiles carried out on moored Acoustic Doppler Current Profiler data sets recorded during the Variability of Exchanges In the Northern Seas project is presented here for several locations in three sections in the vicinity of the Iceland-Scotland Ridge: (1) north of the Faroes, (2) in the Faroe-Bank Channel and (3) in the Faroe-Shetland Channel. Total currents have been decomposed into three components, namely the mean residual flow, tide and surge. The mean residual flow is found to be dominant. Results for the major tidal constituents (M2, S2, N2, O1 and K1) are shown and discussed. It is found that the predominant tidal harmonic M2 becomes steered through depth to align with the bottom topography. The mean residual flow is found to be generally larger than the surge, particularly in the Faroe-Bank Channel below 500m depth where it is the dominant component. Here tidal rectification, i.e. the topographic rectification of tidal currents originating in nonlinearities that rectify the oscillatory tidal motion, is identified as the process enhancing the large mean residual currents found. From the current structure, two water masses are identified in the channel: the upper slowing moving inflow water and the colder outflow water characterised by a 3–6-day periodicity. In the Faroe-Shetland Channel the flow is characterised by large tidal currents, particularly in shallow waters. Instead, north of the Faroes none of the component was identified as dominant. The results show that the variability of the current components is strongly dependent upon topography and water depth. Keywords. Oceanography: Physical (Currents; General circulation; General or miscellaneous)

scholarly journals Improving Estimates of the Antarctic Circumpolar Current Streamlines in Drake Passage

2008 ◽  
Vol 38 (5) ◽  
pp. 1000-1010 ◽  
Author(s):  
Yueng-Djern Lenn ◽  
Teresa K. Chereskin ◽  
Janet Sprintall
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Acoustic Doppler Current Profiler ◽  
Drake Passage ◽  
Meridional Overturning Circulation ◽  
Dynamic Height ◽  
Current Profiler ◽  
Meridional Overturning ◽  
The Mean ◽  
Circumpolar Current

Abstract Accurately resolving the mean Antarctic Circumpolar Current (ACC) is essential for determining Southern Ocean eddy fluxes that are important to the global meridional overturning circulation. Previous estimates of the mean ACC have been limited by the paucity of Southern Ocean observations. A new estimate of the mean surface ACC in Drake Passage is presented that combines sea surface height anomalies measured by satellite altimetry with a recent dataset of repeat high-resolution acoustic Doppler current profiler observations. A mean streamfunction (surface height field), objectively mapped from the mean currents, is used to validate two recent dynamic height climatologies. The new streamfunction has narrower and stronger ACC fronts separated by quiescent zones of much weaker flow, thereby improving on the resolution of ACC fronts observed in the other climatologies. Distinct streamlines can be associated with particular ACC fronts and tracked in time-dependent maps of dynamic height. This analysis shows that varying degrees of topographic control are evident in the preferred paths of the ACC fronts through Drake Passage.

scholarly journals Temporal variations of zooplankton biomass in the Ligurian Sea inferred from long time series of ADCP data

Ocean Science ◽  
2014 ◽  
Vol 10 (1) ◽  
pp. 93-105 ◽  
Author(s):  
R. Bozzano ◽  
E. Fanelli ◽  
S. Pensieri ◽  
P. Picco ◽  
M. E. Schiano
Keyword(s):  
Time Series ◽  
Acoustic Doppler Current Profiler ◽  
Temporal Variations ◽  
Zooplankton Biomass ◽  
Mesopelagic Fish ◽  
Ligurian Sea ◽  
Time Frequency ◽  
Backscattering Strength ◽  
Current Profiler ◽  
Long Time

Abstract. Three years of 300 kHz acoustic doppler current profiler data collected in the central Ligurian Sea are analysed to investigate the variability of the zooplankton biomass and the diel vertical migration in the upper thermocline. After a pre-processing phase aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time–frequency analysis. The effect of changes in the environmental condition is also investigated. The highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern found here points to a "nocturnal" migration, with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also, twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and they are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the available historical acoustic doppler current profiler time series.

scholarly journals Measuring herring densities with one real and several phantom research vessels

2009 ◽  
Vol 66 (6) ◽  
pp. 1264-1269 ◽  
Author(s):  
Ruben Patel ◽  
Egil Ona
Keyword(s):  
Pelagic Fish ◽  
Target Strength ◽  
Fish Biomass ◽  
Marine Science ◽  
Lateral Aspect ◽  
Multibeam Sonar ◽  
The Real ◽  
Backscattering Strength ◽  
The Mean

Abstract Patel, R., and Ona, E. 2009. Measuring herring densities with one real and several phantom research vessels. – ICES Journal of Marine Science 66: 1264–1269. Vessel-induced avoidance can potentially cause a large bias in acoustic estimates of schooling, pelagic-fish biomass. This paper presents a method for quantifying this uncertainty. Volume-backscattering strength (Sv) from a horizontally projecting, multibeam sonar (Simrad MS70) is resampled to form synthetic, vertical, echosounder beams to the side of the survey vessel. These data are analysed as if they were collected from phantom vessels surveying parallel transects at fixed ranges from the real vessel. The nautical-area-backscattering coefficients (sA) from the synthetic echograms are compared with those measured by conventional 70 and 120 kHz echosounders (Simrad EK60) on the real vessel. Data collected in 2006 from schools of Norwegian spring-spawning herring are used to illustrate the method and explore its limitations. Potential effects of vessel-induced avoidance are evaluated by comparing the mean sA values observed from the phantom vessels with those observed from the real vessel. The technique also allows direct estimates of the mean lateral-aspect target strength of in situ herring.

Seasonal changes in the diel vertical migration of Chaoborus punctipennis larval instars

2014 ◽  
Vol 71 (5) ◽  
pp. 665-674 ◽  
Author(s):  
Lauren Emily Barth ◽  
W. Gary Sprules ◽  
Mathew Wells ◽  
Melissa Coman
Keyword(s):  
Vertical Migration ◽  
Diel Vertical Migration ◽  
Acoustic Doppler Current Profiler ◽  
Acoustic Backscatter ◽  
Migration Behavior ◽  
Larval Instars ◽  
Reverse Migration ◽  
Coregonus Artedi ◽  
Chaoborus Punctipennis ◽  
Current Profiler

We describe a novel seasonal shift in the vertical migration behavior of Chaoborus punctipennis second-instar larvae in Lake Opeongo, Ontario. An upward-looking 600 kHz acoustic Doppler current profiler (ADCP) moored at a fixed 22 m station in the lake recorded acoustic backscatter continuously during the study period. Zooplankton samples collected indicated that the abundance of C. punctipennis larval instars accounted for the greatest proportion of variance in the linear backscatter from the ADCP. The large fourth-instar larvae underwent normal diel vertical migration throughout the study. Smaller second-instar larvae underwent reverse migration during late June but switched to normal migration by late July. The acoustic record indicates that the switch occurred over a few days around late June, and at this time a double vertical migration appeared with the second instars leading and following the migration of fourth instars. We speculate that these changes in the migration of second instars are driven by seasonal shifts in predation risk from larval cisco (Coregonus artedi) and by the need to minimize spatial overlap with the larger fourth instars.

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