kHz Acoustic Doppler Current Profiler Research Articles

Krill diel vertical migration: A diagnostic for variability of wind forcing over the Beaufort and Chukchi Seas

Measurements of echo intensities were acquired in shelf waters of the western Beaufort Sea near Utqiaġvik (formerly Barrow), Alaska by upward-looking 307 kHz acoustic Doppler current profilers during a 2008–2015 series of late-summer mooring deployments. These echo signals were analyzed for characteristic patterns of krill diel vertical migration (DVM) from which daily and seasonally-averaged DVM indices (DVMI) were derived. Time varying relationships among DVMIs (inferred krill biomasses) and local and regional wind regimes were diagnosed statistically. The threshold wind speed at which easterly winds promote upwelling of krill onto the western Beaufort shelf occurs at about 6 m s−1. Inferred krill biomass increases on the shelf as upwelling winds relax. Years (2009, 2012) in which inferred krill biomasses were higher on the western Beaufort shelf occurred when average mid-summer winds over the Chukchi Sea were from the south and average late-summer winds over the Beaufort shelf were weak and variable. In contrast, years (2008, 2010–11, 2013–15) in which inferred krill biomasses were lower occurred when average mid-summer winds over the Chukchi Sea were weak and variable and average late-summer winds over the Beaufort shelf were generally easterly and strong.

Kehadiran Gelombang Soliter dan Transpor Sesaat Sedimen tersuspensi di Perairan Pantai Bengkulu Tengah

<strong>Existence of Solitary Waves and Transient Suspended Sediment Transport in the Coastal Waters of Central Bengkulu. </strong>Coastal abrasion and suspended sediment transport driven by waves is occurring dreadfully in the coastal waters of Central Bengkulu. The abrasion tends to be accelerated by solitary waves during the southeast monsoon season. The primary data were obtained on 17-26 July 2014, while the secondary data derived from Google Maps imageries obtained on 17 June 2014, representing the southeast monsoon season. The primary data were collected by 1200 KHz Acoustic Doppler Current Profiler (ADCP) for water currents, a single beam Echosounder for depths, Garmin 276C GPS receiver for coordinate positions, RBR-TWR2050 (installed at at a fixed point at 102.2219 °E and 3.6916 °S and depth of 9 m) for height and wave periods, and a compass for the direction of wave propagation. The secondary data included Astrium satellite imageries compiled by Google Earth and displayed as Google Maps images on 17 June 2014. These images were used for identifying the appearance of wave groups and by using a feature in Google Earth, it showed that the estimated distance between wave packets hitting the coast accounted for 147 m. This study showed the existence of solitary waves with height and wave period of 1.02 m and 13.85 seconds respectively, while the wave length reached 147.7 m. The wave energy and wave energy flux were 1123.12 Jm<sup>-2</sup> and 12018.94 Jm<sup>-1</sup>s<sup>-1</sup>, calculated by using the cnoidal wave theory and solved by the KdV equation. These solitary waves have large destructive forces on unstable cliffs along the coasts. Derived from coastal abrasion processes and shown by the ADCP backscatter intensity with the highest of 146 dB, the suspended sediments were likely to be transported by water currents with an average speed of 25.99 cm s<sup>-1</sup> in the dominant direction to the south - southeast; and the sediments were deposited along the coast of Bengkulu City.

Seasonal patterns in deep acoustic backscatter layers near vent plumes in the northeastern Pacific Ocean

We used moored 75 kHz acoustic Doppler current profilers (ADCPs) to examine seasonal cycles in zooplankton deep scattering layers (DSLs) observed below 1300 m depth at Endeavour Ridge hydrothermal vents. DSLs are present year-round in the lower water column near vent plumes. Temporal variations suggest passive, flow-induced displacements superimposed on migratory movements. Although the strongest DSLs are shallower than the neutrally buoyant plumes (1900–2100 m), anomalies also occur at and below plume depth. Upward movement from plume depth in the main DSL is evident in late summer/fall, resulting in shallower DSLs in winter, consistent with the timing of adult diapause/reproduction in upper-ocean migratory copepods. Movement from the upper ocean to plume depth coincides with pre-adult migration to greater depths in spring. Synchronous 20–40 d cycles in DSLs may account for patchiness in space and time of above-plume zooplankton layers observed in summer during previous net-sampling surveys, and suggests lateral and vertical migratory movements to counter current drift away from plume-derived food sources. Persistent near-bottom DSLs move vertically between the spreading plume and seafloor. Historical net data suggests that these are deep, resident fauna. Unlike upper ocean fauna, they seem to be advected considerable distances from the ridge axis, where they are evident as remnant scattering layers.

Intraseasonal-to-Interannual Variability of the Upper-Layer Zonal Currents in the Tropical Northwest Pacific Ocean

The upper-layer circulation in the Tropical Northwest Pacific Ocean (TNWP) is characterized by the alternating zonal currents, such as North Equatorial Current (NEC) and Subtropical Countercurrent (STCC). The variabilities of the upper-layer zonal currents in the TNWP, which were obtained directly from 75 kHz acoustic Doppler current profiler (ADCP) measurements and indirectly from geostrophic calculations, were investigated on intraseasonal to interannual timescales from 2006 to 2014. Surface geostrophic current derived from sea surface height anomaly (SSHA) approximated well to the in-situ measurements with ADCP that was slightly better than the absolute geostrophic current obtained from AVISO. The interannual signals related to the El Nino-Southern Oscillation (ENSO) were quite apparent, especially near the boundary (about 17.5°N–19°N) between NEC and STCC. We found that the eastward-flowing southern STCC develops during the decaying phase of ENSO and weakens during La Nina. Strong easterlies during strong La Nina (e.g., 2010 La Nina event) seem to influence NEC to expand further north to the southern STCC region and this coincides with the meridional migration of the Sverdrup streamfunction. The southern STCC region is profoundly influenced by the mesoscale/sub-mesoscale eddy activities, which can intensify the eastward flow of STCC and ultimately contribute to the intraseasonal signal. We found that this intraseasonal signal weakened when La Nina happened in 2010, which is presumably associated with the northward expansion of NEC. Possible factors related to the discrepancies between surface geostrophic current and sub-surface ADCP data are discussed.

Estimation of Suspended Sediment Concentration by Using Mobile ADCP Instrument

The measurement of suspended sediment concentration (SSC) by using Acoustic Doppler Current Profiler (ADCP) instrument still not widely used in Indonesia. The application of this technology uses sound wave by four direction transducers placed in the vessel, and this ADCP measured the intensity of backscatter from sediment particles. This study is equipped with RD Instruments WorkHorse Mariner 307.2 kHz ADCP, and the water sample collected from Lembeh Strait, North Sulawesi by using van Dorn bottle sampler. Beyond the experimental purpose of this installation, the interest in having wide area data at different tidal condition is that it provides the possibility of determining the effect of tidal to the SSC. The losses of sound signal were corrected to get more accurate results. Simple linear regression analysis performed to obtain the estimates of the SSC. Estimation of SSC of ADCP measurement was then compared with SSC on water analysis in the laboratory, and the result showed that insignificantly different by statistical analysis. From this research, it showed that the concentration of suspended sediment ranged between 60-73 mg L−1 on location near the Port of Bitung, and 50-62 mg L−1 at a location away from the port. The result also observed that the highest concentration is in the region below the water column, and tidal condition was affected the condition of SSC. Based on all analysis, the mobile ADCP can provide a suitable measurement of suspended sediment concentration.

Pan-Arctic diel vertical migration during the polar night

Diel vertical migration (DVM) has generally been assumed to cease during the polarnight in the high Arctic, although recent studies have shown the occurrence of lunar vertical migrations (LVMs) and shallow DVMs. Here, we quantified when and where full-depth (>20 m), solar-mediated DVM exists on a pan-Arctic scale. We observed the scattering population, most likely to be comprised of zooplankton, using 300 kHz acoustic Doppler current profilers (ADCPs). We quantified the presence/absence of DVM, and found that DVM continues throughout the year to at least 20 m at all locations south of 74° N. North of 77° N, DVM ceases for a period of time duringthe polar night. The dates of this cessation accurately align with the date of the winter solstice (±2 d). Between 74 and 77° N, DVM presence/absence is variable. Acoustic data sampled at 89° N, however, showed no evidence of DVM at any time during the year — a new observation. Using indicators of presence/absence of sea ice from ADCPs and satellite-derived sea ice concentration data, we revealed that local variations in sea ice cover directly determine the continuation or cessationof DVM during the polar night. Earlier-forming and higher-concentration sea ice causes a cessation in DVM, whereas low-concentration or late-forming sea ice results in continuous DVM when comparing migrations at similar latitudes.

Annual Cycle of Turbulent Dissipation Estimated from Seagliders

AbstractThe rate of dissipation of turbulent kinetic energy is estimated using Seaglider observations of vertical water velocity in the midlatitude North Atlantic. This estimate is based on the large‐eddy method, allowing the use of measurements of turbulent energy at large scales O(1–10 m) to diagnose the rate of energy dissipated through viscous processes at scales O(1 mm). The Seaglider data considered here were obtained in a region of high stratification (1 × 10−4<N < 1×10−2s−1), where previous implementations of this method fail. The large‐eddy method is generalized to high‐stratification by high‐pass filtering vertical velocity with a cutoff dependent on the local buoyancy frequency, producing a year‐long time series of dissipation rate spanning the uppermost 1,000 m with subdaily resolution. This is compared to the dissipation rate estimated from a moored 600 kHz acoustic Doppler current profiler. The variability of the Seaglider‐based dissipation correlates with one‐dimensional scalings of wind‐ and buoyancy‐driven mixed‐layer turbulence.

Application of Acoustic Doppler Current Profiler (ADCP) to Observe Diel Vertical Migration of Zooplankton

Study of zooplankton behavior was observed because of their importance as a source energy for small fish and other organisms in the food chain. The aim of this study was to investigate diel vertical migration (DVM) of zooplankton using high frequency acoustic scattering techniques from an acoustic Doppler current profiler (ADCP) instrument. The DVM was observed by utilizing mean volume backscattering strength (MVBS) from the recorded ADCP’s echo intensities. MVBS data were obtained using a bottom-moored, upward looking 750 kHz ADCP at 15 m depth in Lembeh Strait, North Sulawesi, Indonesia. In this work, we simultaneously presented ADCP quantifications, zooplankton net samples, and oceanographic data (tidal and water current). The movement of zooplankton was shallower during the night and deeper during the day with changes of MVBS and ranged between -65 and -80 dB. From laboratory analysis, it was found that crustacean had the highest abundance and biomass, dominated at different time during the observation. However, further research should be performed with specific species using measured sound speed and density of zooplankton and laboratory analysis for grazing angle measurement should be conducted in order to improve accurate results of specific zooplankton.

Prefrontal bore mixing

AbstractRainbow Ridge, a 1950 m deep upthrusted ultramafic block along the axis of the Mid‐Atlantic Ridge, has an active hydrothermal vent system at 2400 m on its western slope. However, within 1 km from the vent excessive temperatures are barely measurable, probably due to strong turbulent mixing. This mixing is studied here using a 400 m long high‐resolution temperature sensor array moored with a 600 m ranging 75 kHz acoustic Doppler current profiler. Rich internal wave turbulence was recorded, characterized by 100–200 m upshoots and >200 m large overturning in particular near the end of the warming phase of the up and down moving tide. These highly nonlinear internal waves of tides interacting with buoyancy frequency waves extend up to 400 m above the sloping bottom of the ridge. While a turbulent “bottom boundary layer” could barely be defined, the more intense turbulence higher up in the water column is suggested to lead to the strong dispersion of the hydrothermal plume.

Use of ADCPs for suspended sediment transport monitoring: An empirical approach

AbstractA horizontally mounted 300 kHz acoustic Doppler current profiler was deployed in Fraser River at Mission, British Columbia, to test its capability to detect size‐classified concentration of suspended sediment. Bottle samples in‐beam provide a direct calibration of the hADCP signals. We also deployed a 600 kHz vertically mounted ADCP from a boat in combination with bottle samples. Fraser River at Mission is 525 m wide with moderate suspended sediment concentration (up to 350 mg L−1 in our measurements, mostly silt), and a modest sand load only at high flows. We use an entirely empirical approach to calculate the sediment load using ADCPs to test the reliability of acoustic methods when assumptions embedded in the sonar equation about the relation between suspended sediment size and concentration, and acoustic signals are violated. vADCP calibration using matched individual bottle samples and acoustic backscatter departed from the expected theoretical relation. Calibration using depth‐averaged sediment concentration and acoustic backscatter more closely matched theoretical expectations, but varied through the season. hADCP calibrations conformed with theoretical expectations and did not exhibit seasonal variation. Silt and sand were successfully discriminated; however, silt dominates the correlations. We found no coherent relation between acoustic attenuation and silt concentration. In‐beam results are extended by correlation to estimate mean sediment concentration and total suspended flux in the entire channel: this auxiliary correlation cancels any calibration bias and permits monitoring of size‐classified suspended sediment in absence of detailed information of sediment grain‐size distribution.

Internal wave–zooplankton interactions in the Alboran Sea (W-Mediterranean)

An upward looking 75 kHz ADCP (Acoustic Doppler Current Profiler) was moored at 100 m above the bottom in 912 m water depth in the central-north Alboran Sea (W-Mediterranean Sea). The ADCP sampled current and acoustic echo-amplitude at a rate of once per minute for 9 days, thereby revealing particular internal wave–zooplankton interactions that varied with depth. The ADCP's echo-amplitude, a measure of zooplankton abundance, showed a dominant diurnal periodicity due to vertical migration, and occasionally intense reflections manifesting high-frequency interfacial internal waves close to the buoyancy frequency. These waves reached excursions of up to about 90 m crest-trough, around 250 m. They were only visible in acoustic data during daytime when the zooplankton gathered near these thin interfacial layers. Around 500 m where the vertical density stratification was 10 times smaller than at 250 m, larger amplitude internal waves were observed, measuring up to about 150 m crest-trough. These waves had the lowest internal wave frequency, close to the inertial frequency. Below 600 m, the stratification was so weak that large (~100 m) vertical convection in the direction of the earth rotational vector dominated over internal gravity waves. At these depths, diurnal vertical migrations were not observed, which suggests that zooplankton either avoid or become dispersed by waters with large vertical convection. Light limitation is not expected to be a key factor in this case, as vertical migration has been observed deeper than 1000 m in other areas where stratification is greater.

Instantaneous movement of krill swarms in the Antarctic Circumpolar Current

Antarctic krill are known to have strong swimming capabilities, but direct observations of the speed and direction of krill‐swarm movement within their natural environment are rare. We identified and examined 4060 swarms within the main flow of the Antarctic Circumpolar Current (Scotia Sea) using a combination of an EK60 echosounder, a 153.6 kHz acoustic Doppler current profiler, and ground‐truthing nets. Net displacement magnitude (m) and net angle of deviation (d) were determined by vector subtraction from the background flow immediately below them. Values were compared against control data sets in which swarms were absent. With greater background flow, m became increasingly lower than predicted, which suggests that drag influences swarm movement. The characteristics of the flow regime influenced swarm behavior, given that both m and d varied according to the direction of background flow. Furthermore, multiple‐regression analysis indicated that swarm area, the vicinity of the sea‐ice edge, and salinity had a significant influence on m, with levels of displacement being greatest in larger swarms and in low‐salinity regions close to the ice edge. The ice edge is a key environment for Antarctic krill and swarm behavior may assist in retaining this location. Only fluorescence was found to have a significant influence on d, with deviations being greatest in regions of highest fluorescence. This agrees with laboratory observations of krill turning more frequently within food patches. We demonstrate that it is possible to measure instantaneous movement patterns in Antarctic krill swarms and, at large scales, these movements are consistent with current understanding of responses of krill to local stimuli such as sea‐ice and patches of food.

Seasonal changes in the diel vertical migration ofChaoborus punctipennislarval instars

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.

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

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.

Direct measurement of volume flux in the Faroe‐Shetland Channel and over the Iceland‐Faroe Ridge

Determining the exchange of water across the Iceland‐Faroe‐Scotland ridge is of fundamental interest because it measures the rate of transformation of North Atlantic water into dense water and thus the strength of the meridional overturning circulation (MOC). Here we study this exchange by monitoring all water flowing through the area east of Iceland to near the bottom or ∼600 m depth using a 75 kHz acoustic Doppler current profiler (ADCP) mounted on the high‐seas ferry M/F Norröna. Starting in March 2008, currents have been measured in the Faroe‐Shetland Channel (FSC) and along the Iceland‐Faroe Ridge (IFR) on the ferry's weekly round‐trips between Iceland and Denmark. The detided average transports (to the north) across the two sections are 4.1 ± 0.1 Sv (106 m2s−1) through the FSC and 4.4 ± 0.25 Sv across the IFR (this excludes ∼1.6 Sv circulating around the Faroes). The Norröna program is ongoing.

Vertical structure and transport of the Antarctic Circumpolar Current in Drake Passage from direct velocity observations

[1] The structure of the Antarctic Circumpolar Current (ACC) in Drake Passage is examined using 4.5 years of shipboard acoustic Doppler current profiler (ADCP) velocity data. The extended 1000 m depth range available from the 38 kHz ADCP allows us to investigate the vertical structure of the current. The mean observed current varies slowly with depth, while eddy kinetic energy and shear variance exhibit strong depth dependence. Objectively mapped streamlines are self‐similar with depth, consistent with an equivalent barotropic structure. Vertical wavenumber spectra of observed currents and current shear reveal intermediate wavenumber anisotropy and rotation indicative of downward energy propagation above 500 m and upward propagation below 500 m. The mean observed transport of the ACC in the upper 1000 m is estimated at 95 ± 2 Sv or 71% of the canonical total transport of 134 Sv. Mean current speeds in the ACC jets remain quite strong at 1000 m, 10–20 cm s −1 . Vertical structure functions to describe the current and extrapolate below 1000 m are explored with the aid of full‐depth profiles from lowered ADCP and a 3 year mean from the Southern Ocean State Estimate (SOSE). A number of functions, including an exponential, are nearly equally good fits to the observations, explaining >75% of the variance. Fits to an exponentially decaying function can be extrapolated to give an estimate of 154 ± 38 Sv for the full‐depth transport.

Comparison of acoustic backscattering techniques for suspended sediments investigation

The aim of this paper is to compare different methods for suspended sediment investigation using the backscattering power of acoustic Doppler current profilers (ADCPs). Different concentration–backscattering models and calibration strategies were compared using two frequencies or only one and accounting or not for sound adsorption due to sediments. Two Teledyne RD Instruments (RDI) ADCPs, working at different frequencies (600 and 1200 kHz), were used simultaneously on the same water column to investigate the suspended sediment concentration and grain size distribution at four cross-sections of a lower Paraná River bifurcation near San Martín city (Argentina). In the same campaign, a Sontek 1000 kHz ADCP previously calibrated with water samples was also used. By applying a mixed electric-acoustical backscatter approach, each RDI ADCP was calibrated on an expected mean concentration, and a homogeneous grain size was fixed among the whole measurement field. Concerning the concentration results, the calibration on the mean value was found to be sufficiently reliable when compared to the previously tested and accepted acoustical backscatter method calibrated against an array of field samples that covered the concentration range of extrapolation. The same electric-acoustic approach was applied for the two frequency method. In this case, the backscatter was calibrated against the expected mean grain size and concentration. Preliminary results concerning the concentration and grain size distribution are consistent with the results of other methods. The quantity and texture of suspended sediments of the Paraná River were found to be consistent with instrument limits in terms of backscattering sensitivity. The wash load did not affect the sound propagation, and sound adsorption due to suspended sand did not perturb the sand concentration assessment.

Multiple frequency acoustic backscatter discrimination of zooplankton and fish scatterers in Cape Cod Bay in Spring 2010.

During the late winter and early spring, Cape Cod Bay has large numbers of marine mammal and seabird predators that feed on aggregations of zooplankton (copepods) and fish (sand lance and herring). As part of a study investigating the foraging behavior of these top predators, we sampled the waters of Cape Cod Bay using multiple frequency (38, 120, 200, and 710 kHz) echosounders and a 600 kHz acoustic Doppler current profiler. To ground truth our data net tows and video plankton recorder casts were used to sample zooplankton, primarily small copepods, while a drop camera system was used to identify aggregations of fish. Combining the backscatter data with target strength estimates for the different scatterer types allowed us to estimate the identity, distribution, and abundance (numerical density) of zooplankton and fish in this area at spatial and temporal scales relevant to the foraging behavior of baleen whales. This method worked best when scattering aggregations were monospecific and target scattering spectra were distinct.

Impact of environmental forcing on the acoustic backscattering strength in the equatorial Pacific: Diurnal, lunar, intraseasonal, and interannual variability

We analyzed several records of mean volume backscattering strength ( S v ) derived from 150 kHz acoustic doppler current profilers (ADCPs) moored along the equator in upwelling mesotrophic conditions and in the warm pool oligotrophic ecosystem of the Pacific Ocean. The ADCPs allow for gathering long time-series of non-intrusive information about zooplankton and micronekton at the same spatial and temporal scales as physical observations. High S v are found from the surface to the middle of the thermocline between dusk and dawn in the mesotrophic regime. Biological and physical influences modified this classical diel cycle. In oligotrophic conditions observed at 170°W and 140°W during El Niño years, a subsurface S v maximum characterized nighttime S v profiles. Variations of the thermocline depth correlated with variations of the base of the high S v layer and the subsurface maximum closely tracked the thermocline depth from intraseasonal to interannual time-scales. A recurring deepening (20–60 m) of the high S v layer was observed at a frequency close to the lunar cycle frequency. At 165°E, high day-to-day variations prevailed and our results suggest the influence of moderately mesotrophic waters that would be advected from the western warm pool during westerly wind events. A review of the literature suggests that S v variations may result from changes in biomass and species assemblages among which myctophids and euphausiids would be the most likely scatterers.

A comparison of acoustic turbulence profiling techniques in the presence of waves

In order to measure turbulent quantities in coastal waters, one must either avoid or confront the confounding effect of waves. In previous work, we have developed a method to cancel waves when using the variance technique to compute Reynolds stress from acoustic Doppler current profiler (ADCP) data. In this paper, we extend this wave cancellation methodology to measurements of turbulent kinetic energy and dissipation using velocities measured along a single acoustic beam. Velocity profiles were collected using a Teledyne/RDI 1,200 kHz ADCP and a Nortek AWAC. The AWAC has a vertical beam that was programmed by Nortek to deliver profiles of vertical velocity. Vertical velocities are desirable both because they eliminate sources of phase error in the wave cancellation procedure and because they constrain measurement uncertainty with respect to turbulent anisotropy. Results indicate that acoustic profiles taken in standard Doppler mode, to which the vertical beam of the AWAC was limited, were too noisy to resolve turbulence under the deployment conditions herein. Pulse-to-pulse coherent modes such as those available on the ADCP were sufficiently low noise to resolve turbulent signals; however, vertical beam data are not available for this device. Nevertheless, our wave cancellation methodology was successful in removing the overwhelming variance associated with waves from both instruments, allowing realistic estimates of Reynolds stress, turbulent kinetic energy, and dissipation from the ADCP. This method holds even more promise as low-noise operating modes are developed for vertical beam acoustic profiling instruments such as the AWAC.