Acoustic Transponders Research Articles

Design and DSP implementation of signal processing module for underwater acoustic transponder

Design and DSP implementation of signal processing module for underwater acoustic transponder

An improved acoustic transponder system via LCCLC impedance matching network and equalization control strategy

AbstractThe underwater acoustic transducer (UAT) generates a large amount of reactive power during the operation, greatly limiting the output capability of the power amplifier. It is necessary to match the UAT and improve its load characteristics. The conventional design methods are not powerful enough to solve nonlinear or parameter‐sensitive problems, lacking enough convergence ability for the network design problem. This article proposes an optimization design method for LCCLC impedance matching network based on the improved chaos optimization algorithm and the corresponding equalization control strategy. First, the impedance model of the UAT is proposed, and then the matching principle of the LCCLC network is analyzed. Based on these, the optimization design for LCCLC network is described in detail. Then, to solve the problem of the calculation of the command signal, a control method based on the FIR filter principle is proposed. Finally, the proposed methods are verified by an experimental platform. The results show that the proposed design method and its corresponding control strategy successfully solve the matching and emission problems.

Autonomous Visual Fish Pen Inspections for Estimating the State of Biofouling Buildup Using ROV

The process of fish cage inspections, which is a necessary maintenance task at any fish farm, be it small-scale or industrial, is a task that has the potential to be fully automated. Replacing trained divers who perform regular inspections with autonomous marine vehicles would lower the costs of manpower and remove the risks associated with humans performing underwater inspections. Achieving such a level of autonomy implies developing an image processing algorithm that is capable of estimating the state of biofouling buildup. The aim of this work is to propose a complete solution for automating the said inspection process; from developing an autonomous control algorithm for an ROV, to automatically segmenting images of fish cages, and accurately estimating the state of biofouling. The first part is achieved by modifying a commercially available ROV with an acoustic SBL positioning system and developing a closed-loop control system. The second part is realized by implementing a proposed biofouling estimation framework, which relies on AI to perform image segmentation, and by processing images using established computer vision methods to obtain a rough estimate of the distance of the ROV from the fish cage. This also involved developing a labeling tool in order to create a dataset of images for the neural network performing the semantic segmentation to be trained on. The experimental results show the viability of using an ROV fitted with an acoustic transponder for autonomous missions, and demonstrate the biofouling estimation framework’s ability to provide accurate assessments, alongside satisfactory distance estimation capabilities. In conclusion, the achieved biofouling estimation accuracy showcases clear potential for use in the aquaculture industry.

Application of deep neural networks for inferring pressure in polymeric acoustic transponders/sensors

Passive sensor-transponders have raised interest for the last few decades, due to their capability of low-cost remote monitoring without the need for energy storage. Their operating principle includes receiving a signal from a source and then reflecting the signal. While well-established transponders operate through electromagnetic antennas, those with a fully acoustic design have advantages such as lower cost and simplicity. Therefore, detection of pressures using the ultrasound signal that is backscattered from an acoustic resonator has been of interest recently. In order to infer the pressure from the backscattered signal, the established approach has been based upon the principle of detection of the shift to the frequency of resonance. Nevertheless, regression of the pressure from the signal with a small error is challenging and has been subject to research. Here in this paper, we explore an approach that employs deep learning for inferring pressure from the ultrasound reflections of polymeric resonators. We assess if neural network regressors can efficiently infer pressure reflected from a fully acoustic transponder. For this purpose, we compare the performance of several regressors such as a convolutional neural network, a network inspired by the ResNet, and a fully connected neural network. We observe that deep neural networks are advantageous in inferring pressure information with a minimal need for analyzing the signal. Our work suggests that a deep learning approach has the potential to be integrated with or replace other traditional approaches for inferring pressure from an ultrasound signal reflected from fully acoustic transponders or passive sensors.

Integrating hydroacoustic and telemetric surveys to estimate fish abundance: a new approach to an old problem

Population abundance is a critical metric in fisheries and conservation, but it is very difficult to measure accurately. Existing estimation methods present significant challenges: mark–recapture methods are time- and labour-intensive, and hydroacoustic echo counting methods face issues with target identity and the habitat types where they can be effectively applied. We present a new methodology for abundance estimation that can improve the reliability of echo counting methods. Split beam hydroacoustic survey data are integrated with telemetry data from fish bearing acoustic transponder tags. These tags are counted by a spatially and temporally concurrent multibeam acoustic survey to produce mark–recapture abundance estimates. We assessed this approach on four wild lake trout populations, ranging in abundance from ∼200 to ∼3000 adults. Our abundance estimates were consistent with those derived from conventional Schnabel and Jolly–Seber mark–recapture studies. We show that the precision achievable with this method in 1 year of field work rivals that provided by long-term (>10 years) continuous mark–recapture studies. We also discuss other ecological questions that could be addressed with this approach.

Passive underwater Acoustic IDentification (AID) tags for enhancing Autonomous Underwater Vehicle (AUV) navigation during docking or homing operations

Autonomous underwater vehicle (AUV) navigation requires accurate positioning information from the surrounding environment, especially for tasks such as AUV homing or docking operations. Previous literature has introduced a class of low-cost passive underwater acoustic markers, termed Acoustic IDentification (AID) tags [Satish and Sabra, J. Acoust. Soc. Am. 149(5), 3387–3405 (2021)] built of multi-layer shells with different acoustic properties and thicknesses to generate a uniquely engineered acoustic signature, composed of the multiple reflections created by the layer interfaces. These passive AID tags can be detected by an AUV instrumented with a high-frequency sonar transducer at significantly greater distances than conventional optical methods, especially in turbid waters. Additionally using AID tags as navigation-aid can also alleviate the need of relying on active acoustic transponders. An implementation of a constellation of AID tags enabling fine underwater positioning an AUV towards a docking station or for homing purposes will be presented to provide proof of concept. Furthermore, the optimization of the design of the AID tags for this application aswell as specific signal processing detection methodologies to improve thedetectability of AID tags in the presence of interfering signals (e.g., clutter) will be discussed. [Work supported by the Office of Naval Research].

Measuring the footprint of fly-dragging gear

The extent and area of seabed swept by fishing gear is necessary information to examine the effects of the fishing on the seabed. We estimated the gear footprint of fly-dragging fishing gear which has not been well studied until now, by measuring its movement. We installed a GPS logger on the fishing boat (80 kW main engine) to determine the its speed and track, acoustic transponder loggers with depth gauges on the heaviest part of the warp (300 m from the boat of the total 712 m in length, called elbows) to determine the distance between the elbows, depth loggers on the head rope and on the ground rope to determine the water depth and the net height, underwater tension loggers connected to the bridles to understand when the tension was transmitted, and speed loggers on the top of the net to determine the speed of the net. Four hauls ranging from 38.6 to 49.6 min from shooting of the marker buoy to retrieval of the net were done. The average distance between the elbows was 302.3 m at the start of the tow, which narrowed to 6.3 m at the end of the tow. The net began to move approximately 3.5 min after the start of the tow, and the speed of the net also increased as the elbow narrowed and the tension increased. The gear footprint which is the area of seabed where either warps or the net passed over was 200,978 m2 on average, which was much larger than the estimated gear footprint of other Japanese demersal towed net that use similar sizes of boats and nets. Demersal seine fishing including the fly-dragging use light and small fishing gear so that it is considered as an ecologically-friendly fishing method compared to otter trawls, but the large gear footprint as estimated in this study may give a negative impact on the seabed environment since the gear would shear off sessile organisms and seaweeds, and flatten the seabed.

Expediting recovery of autonomous underwater vehicles in dynamic mission environments: A system‐of‐systems challenge for underwater warfare

AbstractAs autonomous underwater vehicle (AUV) adoption increases, operators demand advanced behaviors from commercial off‐the‐shelf systems. However, new behaviors can often only be deployed operationally once assured. This paper overviews research into expediting recovery to an operator's vessel through a custom homing behavior, demonstrating technology advancement in conjunction with test and evaluation activities. Advanced docking infrastructure and frameworks are still under development, yet current AUV operations require rapid and reliable recovery when mission factors change. Homing is achieved with a directional acoustic transponder providing range and bearing data to the AUV from the operator's vessel. A converted measurement Kalman filter processes range and bearing data that generates dynamic waypoints for the AUV through MOOS‐IvP as a backseat driver; a universal approach and filtering that is unique from prior AUV research. Results from simulations and field trials were analysed through a modular and experimental Test & Evaluation framework that was adopted specifically to help verify and validate the new AUV behavior, including systematic variations in recovery boat manoeuvres. The process includes documented use for the first time in AUV research of combinatorial screening (high throughput testing) and an average standardized residual metric to focus development early, encourage constructive iteration and build operational and engineering trust. Consistent homing was demonstrated with localization within 0.3 m and homing within 1.8 m of a moving digital acoustic transponder.

The recurring impact of storm disturbance on black sea bass (Centropristis striata) movement behaviors in the Mid-Atlantic Bight.

Storm events are a significant source of disturbance in the Middle Atlantic Bight, in the Northwest Atlantic, that cause rapid destratification of the water column during the late summer and early fall. Storm-driven mixing can be considered as a seasonal disturbance regime to demersal communities, characterized by the recurrence of large changes in bottom water temperatures. Black sea bass are a model ubiquitous demersal species in the Middle Atlantic Bight, as their predominantly sedentary behavior makes them ideal for tagging studies while also regularly exposing them to summer storm disturbances and the physiological stresses associated with thermal destratification. To better understand the responsiveness of black sea bass to storm impacts, we coupled biotelemetry with a high-resolution Finite Volume Community Ocean Model (FVCOM). During the summers of 2016-2018, 8-15 black sea bass were released each year with acoustic transponders at three reef sites, which were surrounded by data-logging receivers. Data were analyzed for activity levels and reef departures of black sea bass, and fluctuations in temperature, current velocity, and turbulent kinetic energy. Movement rates were depressed with each consecutive passing storm, and late-season storms were associated with permanent evacuations by a subset of tagged fish. Serial increases in bottom temperature associated with repeated storm events were identified as the primary depressor of local movement. Storm-driven increases in turbulent kinetic energy and current velocity had comparatively smaller, albeit significant, effects. Black sea bass represents both an important fishery resource and an indicator species for the impact of offshore wind development in the United States. Their availability to fisheries surveys and sensitivity to wind turbine impacts will be biased during periods of high storm activity, which is likely to increase with regional climate change.

Fin whale 40‐Hz calling behavior studied with an acoustic tracking array

Fin whale 40‐Hz calling behavior studied with an acoustic tracking array

Experimental evaluation of passive underwater acoustic markers

Autonomous Underwater Vehicle (AUV) navigation requires accurate positioning information underwater which is most commonly achieved using active acoustic transponders. Such transponders typically require maintenance, power and are not covert. As an alternative, the concept of using passive underwater acoustic markers with layered media for underwater navigation has been previously explored theoretically and experimentally using flat interfaces [Satish et al., JASA-EL 145(1), EL84–EL89]. In order to design passive acoustic markers with a more isotropic scattered response, acoustic markers with curved symmetry were investigated experimentally using scaled ultrasonic testing of 3-D printed concentric hemispheres. Subsequently, larger acoustic markers using acrylic hemispherical shells are constructed and insonified by conventional high-frequency SONAR, and their acoustic signatures are measured and compared to theoretical responses. Tag design considerations and preliminary results for the scattered response from different acoustic markers are compared for uniqueness of acoustic signature.

Interseismic strain build-up on the submarine North Anatolian Fault offshore Istanbul

Using offshore geodetic observations, we show that a segment of the North Anatolian Fault in the central Sea of Marmara is locked and therefore accumulating strain. The strain accumulation along this fault segment was previously extrapolated from onshore observations or inferred from the absence of seismicity, but both methods could not distinguish between fully locked or fully creeping fault behavior. A network of acoustic transponders measured crustal deformation with mm-precision on the seafloor for 2.5 years and did not detect any significant fault displacement. Absence of deformation together with sparse seismicity monitored by ocean bottom seismometers indicates complete fault locking to at least 3 km depth and presumably into the crystalline basement. The slip-deficit of at least 4 m since the last known rupture in 1766 is equivalent to an earthquake of magnitude 7.1 to 7.4 in the Sea of Marmara offshore metropolitan Istanbul.

Passive underwater acoustic tags using layered media.

Autonomous Underwater Vehicle (AUV) navigation requires accurate positioning information from the environment. Existing underwater navigation paradigms employ active acoustic transponders that assist in this task, but these more complex and costly systems require maintenance and power. This paper presents instead a passive underwater marker made of different horizontally stacked acoustically reflective materials that is cost effective and relatively simple to service. A marker's characteristic acoustic signature can be detected by AUVs as acoustic backscattering upon tag insonification, and hence be used for navigation purposes.

Accurate Ocean Bottom Seismometer Positioning Method Inspired by Multilateration Technique

The positioning of ocean bottom seismometers (OBS) is a key step in the processing flow of OBS data, especially in the case of self popup types of OBS instruments. The use of first arrivals from airgun shots, rather than relying on the acoustic transponders mounted in the OBS, is becoming a trend and generally leads to more accurate positioning due to the statistics from a large number of shots. In this paper, a linearization of the OBS positioning problem via the multilateration technique is discussed. The discussed linear solution solves jointly for the average water layer velocity and the OBS position using only shot locations and first arrival times as input data.

Norwegian monitoring (1990–2015) of the marine environment around the sunken nuclear submarine Komsomolets

Norway has monitored the marine environment around the sunken Russian nuclear submarine Komsomolets since 1990. This study presents an overview of 25 years of Norwegian monitoring data (1990–2015). Komsomolets sank in 1989 at a depth of 1680 m in the Norwegian Sea while carrying two nuclear torpedoes in its armament. Subsequent Soviet and Russian expeditions to Komsomolets have shown that releases from the reactor have occurred and that the submarine has suffered considerable damage to its hulls. Norwegian monitoring detected 134Cs in surface sediments around Komsomolets in 1993 and 1994 and elevated activity concentrations of 137Cs in bottom seawater between 1991 and 1993. Since then and up to 2015, no increased activity concentrations of radionuclides above values typical for the Norwegian Sea have been observed in any environmental sample collected by Norwegian monitoring. In 2013 and 2015, Norwegian monitoring was carried out using an acoustic transponder on the sampling gear that allowed samples to be collected at precise locations, ∼20 m from the hull of Komsomolets. The observed 238Pu/239,240Pu activity ratios and 240Pu/239Pu atom ratios in surface sediments sampled close to Komsomolets in 2013 did not indicate any releases of Pu isotopes from reactor or the torpedo warheads. Rather, these values probably reflect the overprinting of global fallout ratios with fluxes of these Pu isotopes from long-range transport of authorised discharges from nuclear reprocessing facilities in Northern Europe. However, due to the depth at which Komsomolets lies, the collection of seawater and sediment samples in the immediate area around the submarine using traditional sampling techniques from surface vessels is not possible, even with the use of acoustic transponders. Further monitoring is required in order to have a clear understanding of the current status of Komsomolets as a potential source of radioactive contamination to the Norwegian marine environment. Such monitoring should involve the use of ROVs or submersibles in order to obtain samples next to and within the different compartments of the submarine.

Comprehensive Analysis of Traveltime Data Collected Through GPS‐Acoustic Observation of Seafloor Crustal Movements

AbstractWe have developed a comprehensive inversion scheme to analyze traveltime data collected through GPS‐acoustic observations on a campaign basis. Our method uses a quantity called the “nadir total delay” (NTD), which is analogous to the zenith total delay in Global Navigation Satellite Systems analyses, to represent the time variation of the sound speed. The observation equation using the NTD is an approximated formulation. We examine its applicable scope using numerical experiments and demonstrate that the approximation holds well enough in practice. Traveltime data from all our observation campaigns were utilized together for inversion calculation to determine the following: (1) the positions of individual precision acoustic transponders at the time of a particular reference campaign, (2) the displacement from these positions of a rigid array at the time of each campaign, and (3) the time variation of the NTD during each campaign. We applied this method to actual data to fix the array geometry more precisely. Also, we have made a first step in detecting vertical motions as well as horizontal motions, though further enhancement of the accuracy will be required. In performing linear regression of array displacements obtained from the inversion, their error covariance has a significant effect on the resulting velocities. When the covariance is taken into account, nearly the same velocities are obtained no matter what campaign is taken as reference in the inversion.

Joint inversion for transponder localization and sound-speed profile temporal variation in high-precision acoustic surveys.

This letter develops a Bayesian inversion for localizing underwater acoustic transponders using a surface ship which compensates for sound-speed profile (SSP) temporal variation during the survey. The method is based on dividing observed acoustic travel-time data into time segments and including depth-independent SSP variations for each segment as additional unknown parameters to approximate the SSP temporal variation. SSP variations are estimated jointly with transponder locations, rather than calculated separately as in existing two-step inversions. Simulation and sea-trial results show this localization/SSP joint inversion performs better than two-step inversion in terms of localization accuracy, agreement with measured SSP variations, and computational efficiency.

A GPS Positioning Method for Underwater Targets Using Dual Acoustic Devices

Since the existing underwater GPS positioning technology can only position underwater targets equipped with acoustic transponders, this study proposed a method of positioning underwater combining targets based on an ultra short baseline forwardlooking sonar acoustic device. The mathematical model of the obtaining longitude and latitude coordinates of the underwater target in the WGS84 ellipsoidal coordinate system was established. A group of data was given based on the measuring state, and Monte Carlo simulation was carried out to study the effects of the random errors in the indirect measurements in the algorithm on the positioning accuracy and the combined effect of the random errors in the indirect measurements in the algorithm on the positioning accuracy at different geological locations. The preset target was measured in the offshore waters of Dalian, confirming the validity of the proposed algorithm.

Hybrid Baseline Localization for Autonomous Underwater Vehicles

This paper presents a hybrid baseline (HBL) navigation method for autonomous underwater vehicles (AUVs). In this approach, a floating acoustic transponder is used to augment moving short baseline (MSBL) navigation, in which two transponders are mounted on a source ship. Kinematic information regarding the floating buoy and source ship are communicated via acoustic messages to the AUV fleet. Simultaneously, clock synchronization and a predefined broadcast cycle enables transponder-to-AUV range estimates based on the acoustic message time-of-flight. Using the extended Kalman (EKF) filter formulation, the broadcasted kinematic information and acoustic ranges are combined onboard each AUV in the fleet to estimate the states of the source ship, the floating transponder, and the AUV itself. Simulation was used to optimize the configuration and performance of the HBL navigation, and field tests were performed to evaluate the navigational performance. In post-processing, high-accuracy position and timing data for the source ship and floating buoy was added to the onboard navigation data in an EKF to recreate the path of the AUV. The accuracy of this post-mission localization was evaluated relative to AUV positions independently measured by an acoustic tracking array at the test facility. The resulting AUV position estimation showed a mean error of 1.59 m, an improvement over the previous result (using MSBL navigation only) of 3.30 m.

Based on Adaptive Notch Filter Design of Underwater Acoustic Transponder for Seismic Exploration in Shallow Sea

Underwater acoustic transponder is widely used in marine underwater acoustic positioning system for high resolution seismic exploration. This paper introduces the structure of underwater acoustic transponder. Analysis of characteristics of underwater acoustic signal, we used Adaptive Notch Filter based on received signal detection. And the result of simulation was given.