Receiver Depth Research Articles

Localizing Snapping Shrimp Noise Using a Small-Aperture Array

In warm shallow waters, one can consistently hear the crackling sound due to snapping shrimp. An individual sound or “snap” is highly impulsive. Knowing the source locations of these snaps facilitates the development of some unique passive sensing applications. One common approach in localizing these snaps is to calculate the time difference of arrival (TDoA) of snaps across sensors of an array. For a snap originating from a short distance away, in terms of a few multiples of the array aperture size, the signal from the snap forms a curved wavefront, such that both the direction of arrival (DoA) and the range of the snap can be obtained by studying the TDoA of the wavefront. However, this method is infeasible for long-range 3-D localization due to the need for large-aperture 3-D arrays. Smaller aperture arrays allow estimation of DoA for far-field sounds, but not the range. Since the ocean surface acts like an acoustic mirror that reflects the snaps, we can estimate the range of the snaps by measuring the TDoA between the direct arrivals and their surface reflections, even if the snaps occur in the far-field of the array. Given a set of perfectly associated direct and surface-reflected snaps, we derive a range estimator parameterized by nominal receiver depth and receiver orientation. In practice, we know these parameters only approximately. The problem is further complicated by the fact that snaps are acoustically similar to each other, and so associating a snap with its surface reflection can be difficult. We propose an algorithm that solves the problem of estimation of snap locations, snap associations, and receiver parameters, jointly. We verify the method through numerical simulation and through experimental results.

Vertical correlations of sound field at large depths in deep water

The research on the vertical correlation characteristics of sound field in deep water has important implications for enhancing the vertical array gain and improving the ability to detect the underwater target. Based on a deep-water experiment conducted in the South China Sea, the vertical coherence of sound fields in the direct zone, shadow zone and convergence zone are analyzed with the sound signals received by a vertical line array that covers the maximal depth to 1,866 m. The numerical analysis based on the ray theory is carried out to provide corresponding theoretical explanations to the variations of the vertical correlation characteristics at different ranges and depths. The vertical correlation coefficients in the direct zone are higher than 0.707 for the whole depth and drop very little with the increase of the vertical depth. It is because the main contributions come from direct arrival ray and sea surface reflection ray. The pulse structure is relatively simple, and the time delays of the two rays increase with the space between two receivers increasing. In the shadow zone, sound energy mainly comes from bottom reflection. Therefore, the vertical correlation coefficients are relatively low. Multi-path arrival is observed obviously. Vertical correlation coefficients drop quickly with depth increasing. With range increasing, the time delays of the multi-path pulses decrease. The vertical correlation coefficients at the same depth will increase a little with range increasing. Near the first convergence zone, vertical correlations oscillate periodically with the increase of vertical separation, and share the same distribution pattern with the sound energy along the vertical direction, which is caused by the periodical oscillation of two groups of the refracted rays from water volume. The refracted rays have the same amplitude, therefore, the time delays of the two group of rays increase with receiver depth increasing, and the phase of sound filed fluctuates in <inline-formula><tex-math id="M1">\begin{document}$The research on the vertical correlation characteristics of sound field in deep water has important implications for enhancing the vertical array gain and improving the ability to detect the underwater target. Based on a deep-water experiment conducted in the South China Sea, the vertical coherence of sound fields in the direct zone, shadow zone and convergence zone are analyzed with the sound signals received by a vertical line array that covers the maximal depth to 1,866 m. The numerical analysis based on the ray theory is carried out to provide corresponding theoretical explanations to the variations of the vertical correlation characteristics at different ranges and depths. The vertical correlation coefficients in the direct zone are higher than 0.707 for the whole depth and drop very little with the increase of the vertical depth. It is because the main contributions come from direct arrival ray and sea surface reflection ray. The pulse structure is relatively simple, and the time delays of the two rays increase with the space between two receivers increasing. In the shadow zone, sound energy mainly comes from bottom reflection. Therefore, the vertical correlation coefficients are relatively low. Multi-path arrival is observed obviously. Vertical correlation coefficients drop quickly with depth increasing. With range increasing, the time delays of the multi-path pulses decrease. The vertical correlation coefficients at the same depth will increase a little with range increasing. Near the first convergence zone, vertical correlations oscillate periodically with the increase of vertical separation, and share the same distribution pattern with the sound energy along the vertical direction, which is caused by the periodical oscillation of two groups of the refracted rays from water volume. The refracted rays have the same amplitude, therefore, the time delays of the two group of rays increase with receiver depth increasing, and the phase of sound filed fluctuates in <inline-formula><tex-math id="M1">\begin{document}$\left[ {0,2} {\text{π}}\right]$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.png"/></alternatives></inline-formula>periodically. The periodicity causes the sound intensity and the vertical correlation coefficients to have the same oscillation structures. If the rays have the same phases, the main contribution comes from refraction rays, the structure of the pulses is relatively simple and causes vertical correlation to be higher. Otherwise, the main contribution comes from bottom reflected rays, the structure of the pulses is complex, and vertical correlation drops down. <b><i>Corresponding Author: Li Zheng-lin</i></b> $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.png"/></alternatives></inline-formula>periodically. The periodicity causes the sound intensity and the vertical correlation coefficients to have the same oscillation structures. If the rays have the same phases, the main contribution comes from refraction rays, the structure of the pulses is relatively simple and causes vertical correlation to be higher. Otherwise, the main contribution comes from bottom reflected rays, the structure of the pulses is complex, and vertical correlation drops down.

Experimental Demonstration of Shadow Zone Localization Using Deep Water Interference Patterns Measured by a Single Hydrophone

This paper discusses the frequency–range interference patterns of the sound field in deep water based on ray theory when the source and the receiver are near the sea surface. Approximate formulas of the frequency–range interference patterns in the shadow zone are derived. In the shadow zone, the sound intensity periodic structure is caused by the interference among the bottom-reflected, bottom–surface-reflected, surface–bottom–surface-reflected, and bottom–surface-reflected rays. The sound intensity changes according to the frequency with two cycles, which increase with the propagation range but decrease with the source and the receiver depths. As a result, the range and depth of the broadband sound source can be extracted from the interference cycles of the sound intensity using a single hydrophone. Interference patterns due to sea-surface broadband noise sources in the shadow zone have been observed in two deep-sea experiments in the South China Sea. Given the high signal-to-noise ratio, the interference cycles can be extracted manually from the time–frequency surfaces. Then, the availability of single hydrophone localization in the shadow zone is verified by experimental data. Compared with the conventional passive source localization methods, this method does not require broadband guide sources, precise seafloor acoustical parameters, or intensive computation of replica fields.

A parallelization of the wavenumber integration acoustic modelling package OASES

The wavenumber integration seismo-elastic model OASES can simulate the wave propagation in layered media, consisting of rough interfaces, elastic and porous layers. The wavenumber integration technique requires only the interesting frequencies, receiver depths, and offsets, to be calculated. As we seek to model pulse propagation at higher frequencies, denser sampling of frequencies must be applied. For complex media with many layers, and many vertical sections, the computation time quickly escalates. By exploiting that each frequency response can be calculated independently, a parallelization of the OASES package has been achieved and is presented here. This makes otherwise unfeasible or unpractical simulations computationally achievable. The parallel OASES package is applied to, and benchmarked on, several acoustic and seismic problems. The increased computation capacity is used to simulate and image the full wave field of several cases, reducing the computation time in one case from 1.5 years to 5 hours.The wavenumber integration seismo-elastic model OASES can simulate the wave propagation in layered media, consisting of rough interfaces, elastic and porous layers. The wavenumber integration technique requires only the interesting frequencies, receiver depths, and offsets, to be calculated. As we seek to model pulse propagation at higher frequencies, denser sampling of frequencies must be applied. For complex media with many layers, and many vertical sections, the computation time quickly escalates. By exploiting that each frequency response can be calculated independently, a parallelization of the OASES package has been achieved and is presented here. This makes otherwise unfeasible or unpractical simulations computationally achievable. The parallel OASES package is applied to, and benchmarked on, several acoustic and seismic problems. The increased computation capacity is used to simulate and image the full wave field of several cases, reducing the computation time in one case from 1.5 years to 5 hours.

CO2 Injection Monitoring Using Transient Electromagnetic in Ground-Borehole Configuration

Using geophysical methods, specifically transient electromagnetic (TEM), for CO2 monitoring is an effective way to detect CO2 diffusion. In this work, a multi-scale finite-difference time-domain (FDTD) algorithm was established to monitor CO2 by defining new iterative relations and approximating boundary conditions, which achieves unification in the time and space domain. The response curve characteristics of different forms of CO2 were acquired by changing the receiver's depth and position, CO2 resistivity, scale, and injection stage. Different models considering a planar, tilted, and large-scale CO2 bodies, which were established to test the capacity of TEM monitoring for CO2. The TEM response of injected CO2 bodies had obvious characteristics and the response curve had distinguishable differences from background. This phenomenon could provide reference models for real TEM CO2 monitoring.

Optimization of deployment depth for active towed array sonar (ATAS) using simulated annealing

The active towed array sonar (ATAS) is an active operating sonar towed behind the surface ship and deployed at various depths. The performance of ATAS may vary with the deployment depth. This study proposes a method which calculates the optimal deployment depth using simulated annealing (SA) in order to reduce the total computational time spent in the direct search of the deployment depth. We define a sonar performance function (SPF) with the probability of detection, which represents as a degree of how well the ATAS might perform at particular deployment depth. Then, the optimal depth is defined as the depth where the SPF is maximized. The SPF depends on the acoustic environment, target position and source-receiver depth. The optimization results are compared with the direct calculation of SPF at all deployment depth of source and receiver. Also, our study provides the optimal depths in the area of East Sea of Korea.

Performance Analysis of Single-Receiver Matched-Mode Localization

Acoustic propagation in shallow water at low frequency is characterized by a few propagating modes. When the source is impulsive or short enough, the modes can be extracted from the signal received on a single sensor using a warping operator. This opens the door to single-receiver matched-mode processing (SR-MMP) as a means to estimate source location and/or ocean environmental parameters. While the applicability of SR-MMP has been demonstrated through several experiments, prediction of its achievable performance has not been fully investigated. In this paper, performance analysis of SR-MMP is carried out using numerical simulations of a typical shallow water environment, incorporating possible environmental mismatch as well as degradations resulting from nonideal modal filtering. SR-MMP is a nonlinear estimation problem that presents three regions of operation: the high SNR asymptotic region driven by local errors, the intermediate SNR threshold region driven by sidelobe ambiguities and the low SNR no-information region. The method of interval errors, which gives computationally efficient and reliable mean squared error performance prediction, is used to conduct the analysis. The results suggest that the SR-MMP performance depends strongly on the source/receiver depth. A significant loss in performance is observed when the receiver is located at a node common to two modes. Receiver depth must therefore be chosen with care. SR-MMP seems to be quite robust to mismatch on the seabed properties alone but does not handle well the combined effect of seabed and water column mismatches. Nonideal modal filtering has a moderate impact on performance.

Altering Vertical Placement of Hydroacoustic Receivers for Improved Efficiency in Coldwater Estuary Zones

AbstractAcoustic telemetry is used to study Atlantic Salmon Salmo salar migration ecology and identify mortality zones within estuary systems. Improved detection efficiency helps reduce the uncertainty associated with survival estimates and improves the accuracy of various migration performance metrics. While emigrating salmon smolts and postsmolts are largely surface‐oriented, using the top few meters of the water column, literature suggests they may sound to 10 m or deeper, influencing detection probability and therefore survival estimates. We determined the influence of receiver depth on detection efficiency to improve telemetry assessments in our coldwater estuary zones. We found significant differences in total detections with experimental depths. Detection efficiency of transmitters improved as much as 18.3% when receivers were placed on the bottom and by 9.2% when receivers were placed at 20 m versus 10 m depth. In a second portion of our study, we evaluated the influence of depth and several environmental variables on detection efficiency using sentinel transmitters. Receivers placed at 20 m depth had greater detection efficiencies than receivers placed at 10 m depth during increased precipitation and wind speed events and at all tide stages. Our results can be used to improve detection efficiency of tagged, epipelagic Atlantic Salmon smolts in coldwater estuary zones.Received November 14, 2016; accepted May 24, 2017Published online August 9, 2017

Streamer depth versus vessel and seismic interference noise

For marine seismic surveying, it is commonly assumed that the noise level decreases with depth. In addition, recent advances in broadband seismic have shown that a greater receiver depth is beneficial in preserving low-frequency data. However, in a heavily trafficked ocean, noise from other ships, including seismic interference, is a counteractive process in which the noise actually varies with depth. Normal modes can be used to explain and predict the ship noise and seismic interference noise level. We find that weather noise is dominant below the first mode’s cutoff frequency (approximately 6 Hz), ship noise is dominant from that frequency to the upper end of the useful seismic frequency band (80 Hz). We have used a data set in which the streamer was towed at 8, 45, and 60 m depths in three passes over the same area in the North Sea. The water depth is 135 m on average. We observe that the noise level at 45 and 60 m depth is approximately 1.6 times stronger than that at 8 m. We find that the air-gun energy is up to 46 dB stronger than the noise from the seismic vessel. However, the total noise from all the ships within several hundred kilometers radius can reduce the data quality.

Advanced processing for UHR3D shallow marine seismic surveys

ABSTRACTTraditionally, commercial ultra‐high‐resolution 3D multichannel seismic surveys have used sources with relatively low‐frequency content (up to 600 Hz) with corresponding relatively low resolution. The new generation of multi‐tip sparkers, however, utilising negative discharge technology, is able to produce repeatable high‐frequency signals (above 2.5 kHz) with the potential to image hundreds of metres of the shallow stratigraphy at < 50 cm vertical resolution. These sources would be especially suited to ultra‐high‐resolution 3D studies such as the foundations of wind turbines installations for offshore wind farms.However, simple downsizing of conventional processing sequences, designed for sources of significantly lower frequency content, is not enough. To preserve the signal properties of the sparker source and produce accurately positioned seismic images, new strategies are needed. The implementation of processing solutions that accurately determine source and receiver depths for all shots is also paramount to correctly reduce the data to the desired vertical datum.A basic methodology for deriving geometry and shot corrections for wave motion and tides from the 3D data themselves has already been demonstrated. With Differential Global Positioning System (DGPS) navigation available on both source and streamers and the correct integration of the seismic recording and positioning systems, this concept has been further developed and refined to be more precise. Being able to derive components of the streamer position and depth is of great importance for effective broadband processing from the slanting streamers that are deployed in acquisition. New procedures and processing techniques have been developed, and their efficacy is demonstrated on case studies of recently acquired 2D and 3D multichannel data.

Array design considerations for exploitation of stable weakly dispersive modal pulses in the deep ocean

Modal pulses are broadband contributions to an acoustic wave field with fixed mode number. Stable weakly dispersive modal pulses (SWDMPs) are special modal pulses that are characterized by weak dispersion and weak scattering-induced broadening and are thus suitable for communications applications. This paper investigates, using numerical simulations, receiver array requirements for recovering information carried by SWDMPs under various signal-to-noise ratio conditions without performing channel equalization. Two groups of weakly dispersive modal pulses are common in typical mid-latitude deep ocean environments: the lowest order modes (typically modes 1–3 at 75Hz), and intermediate order modes whose waveguide invariant is near-zero (often around mode 20 at 75Hz). Information loss is quantified by the bit error rate (BER) of a recovered binary phase-coded signal. With fixed receiver depths, low BERs (less than 1%) are achieved at ranges up to 400km with three hydrophones for mode 1 with 90% probability and with 34 hydrophones for mode 20 with 80% probability. With optimal receiver depths, depending on propagation range, only a few, sometimes only two, hydrophones are often sufficient for low BERs, even with intermediate mode numbers. Full modal resolution is unnecessary to achieve low BERs. Thus, a flexible receiver array of autonomous vehicles can outperform a cabled array.

Geoacoustic Inversion for Bottom Parameters via Bayesian Theory in Deep Ocean**Supported by the National Natural Science Foundation of China under Grant No 11174235.

We develop a new approach to estimating bottom parameters based on the Bayesian theory in deep ocean. The solution in a Bayesian inversion is characterized by its posterior probability density (PPD), which combines prior information about the model with information from an observed data set. Bottom parameters are sensitive to the transmission loss (TL) data in shadow zones of deep ocean. In this study, TLs of different frequencies from the South China Sea in the summer of 2014 are used as the observed data sets. The interpretation of the multidimensional PPD requires the calculation of its moments, such as the mean, covariance, and marginal distributions, which provide parameter estimates and uncertainties. Considering that the sensitivities of shallow-zone TLs vary for different frequencies of the bottom parameters in the deep ocean, this research obtains bottom parameters at varying frequencies. Then, the inversion results are compared with the sampling data and the correlations between bottom parameters are determined. Furthermore, we show the inversion results for multi-frequency combined inversion. The inversion results are verified by the experimental TLs and the numerical results, which are calculated using the inverted bottom parameters for different source depths and receiver depths at the corresponding frequency.

A Simple Method for Source Depth Estimation with Multi-path Time Delay in Deep Ocean**Supported by the National Natural Science Foundation of China under Grant No 11174235.

A method of source depth estimation based on the multi-path time delay difference is proposed. When the minimum time arrivals in all receiver depths are snapped to a certain time on time delay-depth plane, time delay arrivals of surface-bottom reflection and bottom-surface reflection intersect at the source depth. Two hydrophones deployed vertically with a certain interval are required at least. If the receiver depths are known, the pair of time delays can be used to estimate the source depth. With the proposed method the source depth can be estimated successfully in a moderate range in the deep ocean without complicated matched-field calculations in the simulations and experiments.

Vertical amplitude phase structure of a low-frequency acoustic field in shallow water

We obtain in integral and analytic form the relations for calculating the amplitude and phase characteristics of an interference structure of orthogonal projections of the oscillation velocity vector in shallow water. For different frequencies and receiver depths, we numerically study the source depth dependences of the effective phase velocities of an equivalent plane wave, the orthogonal projections of the sound pressure phase gradient, and the projections of the oscillation velocity vector. We establish that at low frequencies in zones of interference maxima, independently of source depth, weakly varying effective phase velocity values are observed, which exceed the sound velocity in water by 5–12%. We show that the angles of arrival of the equivalent plane wave and the oscillation velocity vector in the general case differ; however, they virtually coincide in the zone of the interference maximum of the sound pressure under the condition that the horizontal projections of the oscillation velocity appreciably exceed the value of the vertical projection. We give recommendations on using the sound field characteristics in zones with maximum values for solving rangefinding and signal-detection problems.

Spatial correlation of the high intensity zone in deep-water acoustic field**Project supported by the National Natural Science Foundation of China (Grant Nos. 11434012 and 41561144006).

The spatial correlations of acoustic field have important implications for underwater target detection and other applications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterborne modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.

Data-based depth estimation of an incoming autonomous underwater vehicle.

The data-based method for estimating the depth of a moving source is demonstrated experimentally for an incoming autonomous underwater vehicle traveling toward a vertical line array (VLA) of receivers at constant speed/depth. The method assumes no information on the sound-speed and bottom profile. Performing a wavenumber analysis of a narrowband signal for each hydrophone, the energy of the (modal) spectral peaks as a function of the receiver depth is used to estimate the depth of the source, traveling within the depth span of the VLA. This paper reviews the theory, discusses practical implementation issues, and presents the data analysis results.

Some new observations on the underwater sound field from impact pile driving

The underwater sound field from impact pile driving has been studied in recent years, motivated largely by the high levels and impulsive character of the sound and potential impacts on marine life. Here we report on new observations made on a vertical line array (VLA) and neutrally buoyant geophone (vector sensor) both positioned 120 m from the pile, to inform future modeling and mitigation efforts. These observations include: (1) a ground-wave precursor of amplitude 200 Pa, or 10% of peak pressure (2) delayed arrival structure in the impulsive time series due to injection of airborne sound from the hammering process, and (3) properties of the Scholte wave as a function of receiver depth. The study originates from Puget Sound, WA, and involves a 30-cm diameter steel pile installed with impact hammer energy ~200 kJ. Water depth at pile was 9 m, gradually increasing to 17 m at the VLA range. Pile depth was recorded over the sequence of 300 pile strikes, and this knowledge is essential to interpret these observations as the pile was driven 12 m into the sediment. [Research supported by Washington State Dept. of Transportation with partial support from ONR.]

A time efficient aggregation convergecast scheduling algorithm for wireless sensor networks

We investigated the aggregation convergecast scheduling problem in wireless sensor networks. In order to reduce the time needed for data collection through aggregation convergecast, we propose a scheduling algorithm based on an aggregation tree which enables a small delay lower bound and a time slot allocation method which uses the time slots efficiently. To achieve a small delay lower bound, we take the sum of the receiver's depth and child number as the cost of the transmission links and then construct an aggregation tree gradually by adding to it a link with the minimum cost iteration by iteration. To use the time slots efficiently, we use a neighbor degree ranking algorithm together with a supplementary scheduling algorithm to allocate time slot for the sensor nodes. Experiments show that the proposed scheduling algorithm outperforms other work in most cases by reducing the number of time slots needed for data collection by more than 10 %, which indicates the feasibility of our approach for data collection in wireless sensor networks.

Optimizing the efficiency of a solar receiver with tubular cylindrical cavity for a solar-powered organic Rankine cycle

In this study, a solar collector was considered with a cylindrical cavity receiver. The receiver was a type of coated copper closed-tube open cylindrical cavity. Thermal oil was used as the working fluid in the cavity receiver. The affecting parameters including the concentrator shape, concentrator reflectivity, concentrator optical error, solar tracking error, receiver aperture area, receiver tube diameter, cavity receiver depth, inlet temperature and the mass flow rate of the thermal oil through the receiver were investigated. Also, R141b was considered as the working fluid of the ORC system in the condition of saturated vapor. The main focus of this study was on the thermal modeling and optimization of cylindrical cavity receiver. With the help of the ray-tracing software, SolTrace, and the receiver modeling techniques, the optimum aspect ratios are identified. It is conducted that for attaining higher collector efficiency, higher overall efficiency and higher network smaller tube diameter, optimum height of cavity and lower thermal oil inlet temperature are necessary.

The reflection and shadow effects of seamounts on sound propagation in deep water

The seamounts have enormous effects on sound propagation in deep water. Some abnormal propagation phenomena were observed for two different tracks with the flat bottom and the seamounts bottom environments. A propagation experiment was conducted in the South China Sea in 2014. The effects of seamounts on sound propagation were analyzed by using the wideband signals. It’s observed that, in the first shadow zone about 28 km, the transmission loss (TL) for the environment with the seamounts was decreased up to 7 dB compared with the TL for the environment without the seamounts, due to the reflection effects of the seamount. And in the first convergence zone about 56 km, the TL was increased more than 30 dB for the shallow source. It was because that most of the deep refraction waves were blocked by the seamount. In the reflection zone of seamount, the TL increased as the depth of the receiver became deeper for less of sound rays could arrival and most of the grazing angles became bigger. Moreover, the TL difference between receiver depth 170 and 1868 m was nearly 10 dB. At the range more than 30 km, the TL trends were consistent as receiver depth vary from 170 to 1868 m, because it can be equivalent to that all the rays were reject from the top of the seamount. The numerical TLs and pulse arrival structures can match with experimental results well. Abnormal TLs and pulse arrival structures at different ranges are explained by using ray and wave theory.