During austral summer 2018/2019, we deployed an array of six submerged moorings equipped with Nortek Signature100 integrated wideband echosounder and acoustic Doppler current profilers (ADCPs) on the continental shelf of the northern Antarctic Peninsula. Acoustic data from these instruments were used to classify targets, estimate water flow and the biomass of Antarctic krill ( Euphausia superba ), and quantify krill flux (biomass transport). We differentiated krill from other target aggregations using a supervised classification of data from the echosounder representing five wideband frequency bins spanning 68–113 kHz and two narrowband frequencies at 70 and 120 kHz. We estimated krill biomass using echosounder data collected at 120 kHz and water flow using the ADCP data. We estimated the biomass flux from the product of mean volumetric krill density and flow speed over a depth-integration range of 150 m. The overall mean krill areal biomass density based on hourly averages was 174 g⋅m –2 during the austral summer (December–March). Mean daily biomass decreased by an order of magnitude, from 300 to 31 g⋅m –2 , over the sampling period, and fluctuated by nearly a factor of 4 above and below the local trend within weekly intervals. Mean current direction was along-shelf toward the west, and mean flow speed increased from ∼0.10 to 0.14 m⋅s –1 during the season. Krill flux was correlated with biomass variation, and the grand mean flux was 0.13 g⋅m –2 ⋅s –1 . During the study period and in our approximately 1,300 km 2 study area, average total biomass of krill was 116265 metric tons, and total cumulative krill biomass was 2.5 million tons. Our results demonstrate the utility of integrated echosounder-ADCP systems for quantifying krill flux in an important foraging area used by krill-dependent predators (seabirds and marine mammals) that breed nearby and highlight the scales of variability in a key prey resource required by these predators.

A re-configurable analogue to digital converter (ADC) for underwater acoustic phased array transducers was developed and tested in this study. The ADC achieved a 7.18 effective number of bits resolution with a sampling frequency of 10MHz. It was implemented in a field programmable gate array (FPGA). The proposed method interfaces an array transducer directly with the FPGA using minimal external components and could be fine-tuned for a specific instrument type.

Upper-ocean turbulence is central to the exchanges of heat, momentum, and gasses across the air/sea interface, and therefore plays a large role in weather and climate. Current understanding of upper-ocean mixing is lacking, often leading models to misrepresent mixed-layer depths and sea surface temperature. In part, progress has been limited due to the difficulty of measuring turbulence from fixed moorings which can simultaneously measure surface fluxes and upper-ocean stratification over long time periods. Here we introduce a direct wavenumber method for measuring Turbulent Kinetic Energy (TKE) dissipation rates, ϵ, from long-enduring moorings using pulse-coherent ADCPs. We discuss optimal programming of the ADCPs, a robust mechanical design for use on a mooring to maximize data return, and data processing techniques including phase-ambiguity unwrapping, spectral analysis, and a correction for instrument response. The method was used in the Salinity Processes Upper-ocean Regional Study (SPURS) to collect two year-long data sets. We find the mooring-derived TKE dissipation rates compare favorably to estimates made nearby from a microstructure shear probe mounted to a glider during its two separate two-week missions for (10−8) ≤ ϵ ≤ (10−5) m2 s−3. Periods of disagreement between turbulence estimates from the two platforms coincide with differences in vertical temperature profiles, which may indicate that barrier layers can substantially modulate upper-ocean turbulence over horizontal scales of 1-10 km. We also find that dissipation estimates from two different moorings at 12.5 m, and at 7 m are in agreement with the surface buoyancy flux during periods of strong nighttime convection, consistent with classic boundary layer theory.

Echosounders are widely used to quantify fish behavior, fish stocks, and zooplankton biomass. Acoustic Doppler Current Profilers have also been used to accurately measure currents in all of the world's major water bodies over the last 30 years. The present work evaluates the performance of a combined echosounder/ADCP system, the Nortek Signature100, for simultaneous biomass assessment and current profile data analysis. Due to its combined current profiling and scientific echosounding capabilities, the system is seeing increased usage in biomass flux applications, particularly in Antarctic krill research. However, capabilities of the system are still being studied and the present work aims to expand characterization of its performance. To that effect, a four month deployment was carried out by the French National Center for Scientific Research (CNRS) in the Mediterranean Sea with an up-looking Signature100 mounted atop the ALBATROSS mooring line. The line was at a total water depth of 2420 m and its top was approximately 370 m below the surface. Data show significant variations in scattering conditions between daytime and nighttime due to diel vertical migration (DVM), often unrelated to horizontal velocity fluctuations, highlighting not only the multiple frequency band capabilities of the system (up to 7 bands), but also the strength of the combined echosounder and current profiling functions. Echoview, a commercial software package for hydroacoustic data processing, was used to further explore the spatial and temporal patterns of the organisms observed in the echosounder data. A semi-automated technique was implemented to efficiently and objectively clean (e. g. remove interference generated by passing ship traffic), classify (e.g. based on relative frequency response or morphology), and characterize the narrow bandwidth and pulse compressed echosounder data by generating outputs that can contribute to the management and monitoring of aquatic resources.

Here we present the development of a short range (0.5 to 20 m), low cost (<; USD 5,000), three-beam, 1 MHz acoustic Doppler current profiler called the Nortek ECO. The system employs a robust wideband velocity measurement technique where the only required user inputs are: 1) when deployment should start, 2) how often to sample, and 3) what is the water type. The hardware is highly portable, measuring only 130 mm tall by 85 mm in diameter and weighing 1.0 kg in air. It communicates externally with Bluetooth Low Energy technology, and is powered by an embedded smart Li-Ion battery that is charged by induction. Three independent activation methods are implemented, including Near-Field Communication, and all communication controlled via a platform-independent Progressive Web App. Coupled with the ADCP is a deployment and recovery system allowing for single-person operation at depths up to 50 m. Discussion of the system concept and design are presented, including sample data.

Improvements to motion compensation in current profile data from surface buoys have been previously presented [1] and here we expand on this previous work on the integration of Attitude and Heading Reference Sensors (AHRS) to Acoustic Doppler Current Profilers (ADCP). Presently, the applicability of surface buoy-mounted ADCPs is generally limited to those applications where spatial and temporal averaging are acceptable methods to address motion concerns. However, the increasing demand from both the research and operational communities for ever finer resolution in space and time is rendering averaging as an unacceptable method for these type of deployments. But recent technological advances in miniature gyro-compensated motion sensors (improved accuracy and resolution, and reduction in physical size, power consumption, and cost) addresses some of the earlier concerns with surface buoy-mounted ADCPs. This is achieved through real-time bin mapping at the individual ping level where true tilt data is derived from the AHRS, as opposed to non-gyro-compensated tilt sensors that are the norm for ADCPs up to now. These advances allow for more precise validation of surface buoy-mounted ADCP data against static-mounted reference systems. Data from test deployments is presented, including comparison with reference systems, as well as comparison with simulated “standard” tilt sensors.

The Surface Wave Instrument Float with Tracking (SWIFT) is a freely drifting platform for measurements of waves, currents, and turbulence in the ocean surface layer. This platform has been used globally to study wave breaking, wave-current interactions, and waves in ice. A new version (v4) of the buoy has recently been developed and demonstrated in the Office of Naval Research "Langmuir Circulations" field campaign along the California coast (2017). The new version is built around a 5-beam Acoustic Doppler Current Profiler (Nortek Signature 1000) with a multi-pulse coherent mode for high-resolution turbulence measurements. The new Doppler profiler enables estimates of the turbulent dissipation rate down to 3.5 m below waves, compared with 0.5 m in the previous version, and can measure a much larger range of turbulence levels than the previous version. The new version also uses a broadband Doppler mode to profile the mean currents down to 20 m. Mean Eulerian velocity profiles are estimated from the wave-averaged profiler velocities by applying a wave-following bias correction that scales with the Stokes drift and has twice the vertical decay scale. Finally, the new version supports real-time telemetry of raw sea surface elevations for reconstruction of individual waves by processing a coherent array of multiple SWIFTs, with applications for short-range wave-by-wave forecasting. These combined improvements to the platform are intended to advance understanding of wave processes and applications in the ocean surface layer.

The present work describes a newly-developed Acoustic Doppler Current Profiler (ADCP) that has a fully integrated single-beam wide-band biological echosounder, thus serving a dual purpose: current measurement and biomass assessment. The system comprises a traditional 4-beam Janus configuration head, which is responsible for profiling the currents, with a vertically oriented center beam for collecting high-resolution acoustic backscatter data for subsequent biomass analysis. The system belongs to the Signature Series family of ADCPs launched in 2013 by Norwegian scientific instrumentation company Nortek. Named Signature100, it is powered by the AD2CP electronics platform, described in United States Patent 7.911.880. The four slanted beams (current profiling beams) operate at a center frequency of 100 kHz and have a range of up to 400 m with 4 m spatial resolution and sampling rate up to 1 Hz. The center vertical beam (echosounding beam) has a wider frequency band of approximately 70-120 kHz with a high dynamic range (~130 dB), and presently operating in up to three discreet pulse characteristics from a single beam set: 1) 70 kHz monochromatic, 2) 120 kHz monochromatic, and 3) 91 kHz chirp with 50 percent bandwidth and pulse compression. Acoustic pulses from the echosounder beam are interweaved with pulses for the current profiling beam for synchronous data collection. In this work we describe the system's configuration, capabilities and results from initial trials.

The present work focuses on improving motion compensation in current profile data from surface buoys by integration of an Attitude and Heading Reference Sensor (AHRS) to a state-of-the-art Acoustic Doppler Current Profiler (ADCP), thus expanding its use into applications where fine spatial and temporal resolutions are desired. Presently, the applicability of surface buoy-mounted ADCPs is generally limited to those applications where spatial and temporal averaging are acceptable methods to address motion concerns. However, the increasing demand from both the research and operational communities for ever finer resolution in space and time is rendering averaging as an unacceptable method for these type of deployments. But recent technological advances in miniature motion sensors (improved accuracy and resolution, and reduction in physical size, power consumption, and cost) promises to address some of the earlier concerns with surface buoy-mounted ADCPs by enabling realtime bin mapping at the individual ping level. Additionally, these advances allow for more precise validation of surface buoy mounted ADCP data against static-mounted reference systems.

This paper describes the instrumentation and techniques for long-term targeted observation of the centimeter-scale velocity structure within the oceanic surface boundary layer, made possible by the recent developments in capabilities of autonomous platforms and self-contained pulse-coherent acoustic Doppler current profilers (ADCPs). Particular attention is paid to the algorithms of ambiguity resolution ("unwrapping") of pulse-coherent Doppler velocity measurements. The techniques are demonstrated using the new Nortek Signature1000 ADCP mounted on a Lagrangian float, a combination shown to be capable of observing ocean turbulence in a number of recent studies. Statistical uncertainty of the measured velocities in relation to the ADCP setup is also evaluated. Described techniques and analyses should be broadly applicable to other autonomous and towed applications of pulse-coherent ADCPs.

Acoustic Doppler velocimeters (ADVs) are a valuable tool for making high-precision measurements of turbulence, andmoorings are a convenient and ubiquitous platform for making many kinds of measurements in the ocean. However, because of concerns that mooring motion can contaminate turbulence measurements and that acousticDoppler profilersmakemiddepth velocitymeasurements relatively easy, ADVs are not frequently deployed from moorings. This work demonstrates that inertial motion measurements can be used to reduce motion contamination from moored ADV velocity measurements. Three distinct mooring platforms were deployed in a tidal channel with inertial-motion-sensor-equipped ADVs. In each case, motion correction based on the inertial measurements reduces mooring motion contamination of velocity measurements. The spectra from these measurements are consistent with other measurements in tidal channels and have an f25/3 slope at high frequencies-consistent with Kolmogorov's theory of isotropic turbulence. Motion correction also improves estimates of cross spectra and Reynolds stresses. Acomparison of turbulence dissipation with flow speed and turbulence production indicates a bottom boundary layer production-dissipation balance during ebb and flood that is consistent with the strong tidal forcing at the site. These results indicate that inertial-motion-sensor-equipped ADVs are a valuable new tool for making high-precision turbulence measurements from moorings.

The Vectron is a new pulse-coherent Doppler sonar system that has been developed to allow remote measurement of turbulent velocities at mid-water depth (O 10 m distant from the instrument transducers) to meet the measurement and monitoring needs of the in-stream tidal generating industry. Multiple sonar units (based on the Nortek AD2CP hardware platform) are networked together and the instrument is configured with a modular philosophy that allows a great deal of flexibility in acoustic sampling schemes. Time synchronization between the essentially independent instruments is achieved through a low latency Ethernet switch using a master Precision Time Protocol (PTP) clock. Pulse-to-pulse coherent sampling is achieved by taking advantage of bistatic beam geometries that isolate a small sample interval (at 7 m from the central transducer). Velocity ambiguity is overcome using a completely new technique based on multiple computations of the pulse-to-pulse correlations. A prototype system was deployed from a wharf in Parrsboro (Nova Scotia) where turbulent flows with mean velocities up to about 2 m/s were observed. Velocity power spectra are presented and compared to reference observations from a nearby single-point flowmeter.

When designing ADCPs, we trade off profiling range, vertical resolution and energy consumption. The last point is restricted by the availability of batteries and is usually fixed for a planned deployment. The first two points are intertwined in a complex relation because good vertical resolution requires both short acoustic pulses and a reasonably wide bandwidth, both of which lead to shorter range. As such, it is hard to reach any breakthrough in the range-resolution characteristics of an ADCP without finding a completely new approach to estimating velocity from the acoustic echo. Against this backdrop, our development of a new long range current profiler focused on optimizing each element in the system that we could control, from transducer design to mechanical design, from power consumption to profiling range, and from interfacing to data storage. Combined with a very flexible timing controller, this novel system provides the basis for a new generation of current profilers where the hardware platform is referred to as AD2CP, of which the Signature75 long range current profiler is the first fully commercial implementation. In a recent test outside Toulon France, the system functioned every bit as efficiently as we could have hoped and collected velocity data over a profiling range exceeding 900 meters in the Mediterranean.

Nortek provides a combined wave and current profiling instrument in the form of the AWAC. This variant of the traditional ADCP has managed to circumvent the classic limitations of measuring short waves in deep waters by introducing a vertical beam that directly measures the height of the water-air interface (waves) above the instrument. This same vertical beam has also demonstrated that it is capable of measuring the distance to the water-ice interface, and as a result can be used as means to estimate ice draft or ice thickness. Measurement campaigns that have taken place in relatively shallow coastal waters (less than 50 meters) are finding themselves more often in deeper waters. These deployments are also occurring at more extreme latitudes where the presence of ice is more common. This means that common measurement requirements now include measuring ice thickness in addition to current profiles and directional wave observations. Nortek has addressed this need of measurements in deeper waters by building upon the success of the AW AC. A 400 kHz AWAC has been developed and intended for deployment depths of 100 meters. The 400 kHz AWAC is outfitted with a temperature compensated pressure sensor and firmware with a dual functioning surface tracking measurements for ice and waves. The wave burst measurement contains detection methods for both water-air interface and water-ice interface; this means the AWAC can transition seamlessly from wave measurements in the summer to ice measurements in the winter. Ice thickness data is presented for two AWACs deployed in the Beaufort Sea, Alaska. These data are compared to an ASL ice profiler. AWAC data was collected in a special diagnostic mode and allowed for the user to select the best water-ice interface detection method in post-processing. The results show that there is favorable agreement between the AWAC and the ASL ice profiler. This data set was useful in developing the now existing firmware used to detect the water-ice interface. These shallow water data did not illustrate errors associated with an unknown speed of sound profile which is identified as the primary source of error for the AST distance measurement. Additionally, wave results are presented for the 400 kHz AWAC and compared to a 600 kHz AWAC, which was deployed in the vicinity. The data show that non-directional estimates agree well, however directional estimates are complicated by the fact that the two AWACs were deployed at different locations and exposed to different wave directions due to local refraction. It is clear that another comparison test needs to be conducted with the reference instrument collocated with the 400 kHz AWAC.

The EasyQ is a compact sensor that measures river flow velocity and water level (stage). It is appropriate for monitoring river discharge at sites where velocity is needed to supplement stage measurements. In the longer term, its ability to provide sufficient data to automate quality control will improve routine dissemination of river flow data. The EasyQ produces data specifically to support automated data quality control. It measures velocity and signal strength in three cells, thus enabling validation of the data by comparison of the different cells. An integrated pressure sensor plus two independent stage quality parameters provide means to validate and automatically correct stage measurements. A fourth beam enables the EasyQ to detect changes in the depth of the nearby channel. This report summarizes two test comparisons of the EasyQ with nearby sensors. In the White River, comparison of EasyQ velocities with other nearby velocity sensors shows that the EasyQ's velocity measurement is accurate to around 1%. Comparison with a nearby AVM shows that the EasyQ velocity is proportional to the velocity averaged across the full width of the river. This result suggests that an EasyQ's velocity, measured at the side, can produce index velocities appropriate for estimating the discharge of the river. At Fall Creek, the EasyQ stage readings matched a nearby shaft encoder with a standard deviation of 4.7 mm. The EasyQ flagged several of its stage data points bad, and its pressure sensor provided the basis for accurate reconstruction of the missing data.