Sea Noise Research Articles

Characterization and modeling of wind-dominated ambient noise in South China Sea

Characterization and modeling of wind-dominated ambient noise in South China Sea

Ambient noise dynamics in a heavy shipping area

The management of underwater noise within the European Union's waters is a significant component (Descriptor 11) of the Marine Strategy Framework Directive (MSFD). The indicator related to continuous noise, is the noise levels in two one-third octave bands centered at 63Hz and 125Hz. This paper presents an analysis of underwater noise in the Celtic Sea, a heavy shipping area which also hosts the seasonal Ushant thermal front. In addition to the MSFD recommended frequency bands, the analysis was extended to lower and upper frequency bands. Temporal and spatial variations as well as the influence of the properties of the water column on the noise levels were assessed. The noise levels in the area had a high dynamic range and generally exceeded 100dB re 1μPa. Finally, the results highlighted that oceanic mooring must be designed to minimize the pseudo-noise and consider the water column physical properties.

Corrugated-Diaphragm Based Fiber Laser Hydrophone with Sub-100 μPa/Hz1/2 Resolution.

In this work, a beat-frequency encoded fiber laser hydrophone is developed for high-resolution acoustic detection by using an elastic corrugated diaphragm. The diaphragm is center-supported by the fiber. Incident acoustic waves deform the diaphragm and induce a concentrated lateral load on the laser cavity. The acoustically induced perturbation changes local optical phases and frequency-modulates the radio-frequency beat signal between two orthogonal lasing modes of the cavity. Theoretical analysis reveals that a higher corrugation-depth/thickness ratio or larger diaphragm area can provide higher transduction efficiency. The experimentally achieved average sensitivity in beat-frequency variation is 185.7 kHz/Pa over a bandwidth of 1 kHz. The detection capability can be enhanced by shortening the cavity length to enhance the signal-to-noise ratio. The minimum detectable acoustic pressure reaches 74 µPa/Hz1/2 at 1 kHz, which is comparable to the zeroth order sea noise.

Anthony Hawkins—A pioneer of fish bioacoustics

For over 50 years since his first description of underwater sounds by the haddock (Melanogrammus aeglefinus), Anthony (Tony) Hawkins has investigated numerous topics on fish bioacoustics and has been a leading pioneer in examining the production and reception of sound by fishes and more recently the impacts of anthropogenic sounds on fishes. Tony has worked on a diverse number of fish species including commercially important species such as the cod (Gadus morhua) and the Atlantic salmon (Salmo salar). He has investigated a number of important bioacoustic research topics that range from investigating the acoustic properties of swim bladders, examining how behaviorally-relevant sounds can be masked by sea noise, and determining the directional hearing sensitivities and capabilities of fishes. Throughout his career, Tony has strived to perform behavioral experiments on fish under the appropriate biologically relevant acoustic conditions in the natural environment, which can often be a more difficult but an effective and rewarding approach to conducting fish bioacoustic experiments. His classic experiments and important research findings on fish hearing are still referenced today and are regularly used in environmental impacts statements to estimate the hearing capabilities of fishes.

Characteristics of snapping shrimp noise in the northeastern East China Sea

Snapping shrimp sounds are a dominant source of high-frequency ambient noise (e.g., > 1 kHz) in temperate and tropical coastal waters of depths less than 60 m. Surprisingly, a recent shallow water experiment conducted in the northeastern East China Sea (SAVEX15) revealed an abundance of snapping shrimp sounds in approximately 100-m deep shallow water from two 16-element vertical line arrays (VLAs) deployed over 10 days. Our preliminary analysis indicates the pressure amplitude statistics fits a SαS (symmetric alpha-stable) distribution due to a heavy tail over the commonly assumed Gaussian distribution, while the temporal statistics of shrimp snaps detected above some threshold appears to fit a non-homogeneous Poisson process. In addition, the VLAs allow for localization of individual snapping shrimp. In this paper, the temporal and spatial variability of the noise characteristics dominated by snapping shrimp sounds are investigated in the northeastern East China Sea.

Acoustic and Ultrasonic Detection With Radio-Frequency Encoded Fiber Laser Sensors

Fiber lasers have been exploited as sensors for the detection of extremely weak mechanical parameters, by monitoring the radio-frequency beat signal between orthogonal polarized lasing modes. This sensor scheme has presented advantages including advanced measurement capability, low cost and convenience in signal demodulation, resistance to environmental disturbances, and intrinsic multiplexing capability. Here, we demonstrate the capability of the fiber laser sensors for the detection of low-frequency ( 1 MHz (denoted as “high frequency” in this paper) and around 200 kHz (denoted as “medium frequency”), toward different applications. For low-frequency acoustic sensing, the detection limit reaches 74 μPa/Hz1/2 at 1 kHz which is comparable to the zeroth-order sea noise. For high-frequency ultrasound detection, the laser sensor presents a detection capability of 40 Pa over 50 MHz bandwidth, which allows its application as an ultrasound detector in photoacoustic (PA) imaging. Preliminary three dimensional PA imaging is presented, by means of time-to-space reconstruction. Ultrasound detection with a polymer-packaged fiber laser at 100 kHz range is demonstrated, which could find applications in underwater search and targeting. Its imaging capability is also exhibited.

Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea

Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~20dB at a frequency of 125Hz, and ~10dB on average over 10–1000Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning.

Ambient Noise Analysis and Modeling in Shallow water of Arabian Sea

work presents a shallow water ambient noise analysis and modeling effort in the Arabian Sea. Real ambient noise recording at very shallow depths has been analyzed for two environmentally unique periods when the sound velocity profile and the wind conditions present distinct characteristics. Ambient noise data were collected for January and March in the shallow water of Arabian Sea between the wind speed 0.0 m/s to 4.11 m/s. The relative spectral energy distribution of sea noise is presented for a number of wind speeds. Linear relationship between the sea noise spectrum levels and the wind speed were found for the entire frequency range, but the slope were frequency dependent. The results of empirical fitting based on the analysis were used for noise level prediction and the model predictions were compared with the measured noise level. Such study post extensive validation has the potential to develop predictive models for ambient noise estimation based on recorded data. dependent coefficient. The ambient noise was also shown to be site specific in shallow water where speed of the sound and the bottom properties vary substantially with the location. Gayer & Wille (1984) in their work made measurements in North Sea and Baltic Sea and reported that the influence of propagation loss on the wind dependent shallow water noise appears to be marginal even at extremely different area. It was observed that the contradicting behavior of the summer and winter noise levels was due to wind stress at sea surface. Similar work by Ingenito (1989) on site dependence of wind- dominated ambient noise in shallow water reported lower noise level of around 2 dB in the silt bottom at wind speed of 7 m/s when compared to sand bottom at wind speed 3-5 m/s and variability of 10 dB in the average noise spectrum level was observed in the essential fraction of the entire range of the spectrum. The large spread of wind generated noise levels measured for the same wind speed and wave height in the absence of other noise sources is essentially attributed to the site dependence and the primary site dependent factor that influence the noise level being acoustic propagation which in turn are dependent on the season, ocean depth and the bottom composition . Piggott (1964), has reported a logarithm relation for the ambient noise and the wind speed based on his study at two depths in very shallow water (36 m and 51 m), where the non wind dependent factors were reported to be not significant and the contribution of the wind dominated source was observe to be dominant at nearly all wind speeds and all frequencies. The relation has been extensively validated by numerous researchers and adapted for varying sites. The relation is presented below for reference:

Seasonal and diel variability of the underwater noise in the Baltic Sea

The results of ambient sea noise measurements performed in strongly stratified shallow basins in the southern Baltic Sea are presented. The experiments were conducted with an autonomous hydroacoustic buoy that was equipped with two omnidirectional hydrophones located inside and outside the seasonal waveguide. Data were collected in two areas with contrastingly diverse sound propagation conditions-at the Bornholm Deep in winter and at the Gdansk Deep in summer. The noise spectrum levels indicate a strong dependence on the sound propagation conditions (season, location) and show significant differences with the observation depth. At frequencies f < 1 kHz, the noise at the same wind speeds is approximately 10-15 dB higher in winter than in summer. The wind-driven component of the noise frequently does not match the patterns of the Knudsen curves. Furthermore, the noise demonstrates the diel variability. The relative differences of the noise spectrum levels inside and outside of the subsurface winter waveguide reveal regular changes by as much as 15 dB, and are the most visible in the frequency range of 1-2 kHz after sunset. The changes are synchronized with the vertical migration of marine organisms and correspond to the resonant frequencies of the fishes' swim bladders.

Suppression of Underwater Noise Induced by Cavitation: SONIC

In EU FP7 project SONIC, partners set out in October 2012 to study the underwater radiated noise of ships and shipping. The objectives of the project were (1) to study the numerical and experimental techniques to determine the underwater noise; (2) to develop methods for mapping the noise of ships and shipping; and (3) to determine mitigation measures to reduce the underwater radiated noise.Numerical methods focused on determination of the cavitation extent and dynamics on propellers which is the main source of noise of commercial shipping. Research also focused on methods to determine the underwater radiated noise from machinery. Experimental methods in model test facilities have been studied and validated against dedicated full scale measurements. The ship noise source levels obtained from these numerical and experimental methods provide input to shipping noise mapping tools to determine the overall underwater noise in a certain sea area.Based on the experience gained in the SONIC project, a set of guidelines for regulators concerned with underwater radiated noise of ships were developed together with the AQUO project. These guidelines discuss the definitions, numerical and experimental methods and mitigation solutions for underwater radiated noise.This paper gives an overview of the work done by all partners in the SONIC project.

Regional Variations and Trends in Ambient Noise: Examples from Australian Waters.

Studies of ambient noise south of Australia show higher levels at low frequencies in the deep water off the continental shelf compared with locations on the shelf. The difference arises because of differences in transmission loss. Marine animals would experience significantly different noise levels and directionality in the two regions and while crossing the boundary, provide positional information. Opportunities for long-range, low-frequency communication by animals would be significantly limited by the higher background noise in the open ocean. Measures of long-term sea noise trends highlight the influence of biological sources and the importance of local sound transmission regimens.

Reflection loss estimation using shallow water ambient noise in the Arabian Sea off the west coast of India

This study focuses on the application of a recently developed array processing technique, for estimating the seabed reflection loss, using ambient noise in extremely shallow water (Siderius et al, 2013). According to synthetic array processing technique, the angular resolution of directionality and reflection loss derived from ambient noise can be improved. In this method, Toeplitz property of noise coherence function is used to improve the angular resolution in beamforming. The simulated result of the developed technique provides higher angular resolution for vertical directionality and reflection loss. Ambient noise data recorded in wind prevailing conditions, using a 12 element vertical array from the shallow waters off the west coast of India was used for the analysis. The results from the experimental data conclude that, the reflection loss derived from a 12 element physical array can achieve angular resolution, comparable to a synthetically expanded 6 element physical array.

Mobile Equipment for Hydro-Acoustic Parameters Measurement

During construction and during exploitation operations of the offshore objectives occurs, inevitably, noise pollution in the marine environment. This paper presents a system for measuring underwater acoustic field. The mobile polygon is described, which is used in noise measurements for the determination of sea noise.

Shipping noise affecting immune responses of European spiny lobster (Palinuruselephas)

Marine crustaceans are influenced by numerous environmental factors. Environmental stress from pollutants seems to affect their metabolism, growth, moulting, survival, and immune defence. Recently, it has become clear that there is an impact of the global increase in sea noise levels due to shipping traffic on crustacean welfare. Considering the ecological and commercial importance of the European spiny lobster (Palinurus elephas (Fabricius, 1787)) in most parts of the Mediterranean coastal area, in the present study we investigated whether shipping noise pollution contribute to changing the immune parameters of stress in the European spiny lobster. The animals were exposed to a mix of noises produced by different typologies of the boat played back in a tank, and the values of cellular and humeral parameters were evaluated. Total haemocyte count (THC), haemolymphatic protein concentration, phenoloxidase (PO) activity in cell-free haemolymph, and heat shock protein 27 (Hsp27) expression in haemocyte lysate were considered potential biomarkers of stress. THC and PO activity decreased significantly, whereas total protein and Hsp27 expression increased significantly. Overall, the results demonstrate that the stressful conditions investigated in this study affect both cellular and biochemical parameters in the European spiny lobster.

Marine target detection in quad-pol synthetic aperture radar imagery based on the relative phase of cross-polarized channels

A focus on marine target detection in noise corrupted fully polarimetric synthetic aperture radar (SAR) is presented. The property of the relative phase between two cross-polar- ized channels reveals that the relative phases evaluated within sea surface area or noise corrupted area are widely spread phase angle region ½−π; π� due to decorrelation effect; however, the rel- ative phases are concentrated to zero and � π for real target and its first-order azimuth ambi- guities (FOAAs), respectively. Exploiting this physical behavior, the reciprocal of the mean square value of the relative phase (RMSRP) is defined as a new parameter for target detection, and the experiments based on fully polarimetric Radarsat-2 SAR images show that the strong noise and the FOAAs can be effectively suppressed in RMSRP image. Meanwhile, validity of the new parameter for target detection is also verified by two typical Radarsat-2 SAR images, in which targets' ambiguities and strong noise are present. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.9

The effect of ocean fronts on acoustic wave propagation in the Celtic Sea

Underwater noise is now classed as pollution in accordance with the Marine Strategy Framework Directive. Noise from shipping is a major contributor to the ambient noise levels in ocean, particularly at low (<300Hz) frequencies. This paper studies patterns and seasonal variations of underwater noise in the Celtic Sea by using a coupled ocean model (POLCOMS) and an acoustic model (HARCAM) in the year 2010. Two sources of sound are considered: (i) representing a typical large cargo ship and (ii) noise from pile-driving activity. In summer, when the source of sound is on the onshore side of the front, the sound energy is mostly concentrated in the near-bottom layer. In winter, the sound from the same source is distributed more evenly in the vertical. The difference between the sound level in summer and winter at 10m depth is as high as 20dB at a distance of 40km. When the source of sound is on the seaward side of the front, the sound level is nearly uniform in the vertical. The transmission loss is also greater (~ 16 dB) in the summer than in the winter for shallow source while it is up to ~20dB for deep source at 30km.

Noirse-Made-Earsy:

It has been said that “anybody who takes ‘Finnegans Wake’ as an ur-text will probably have a low signal to noise ratio.”1 Doubtless any meaningful signal that the reader of the Wake receives must be separated from a much larger background of confusion and dissonance. Another way of looking at it, however, is that noise is inseparable from the process of sense making. In this study I use such theoreticians of noise as Jacques Attali, Michel Serres, and Avital Ronell to show how noise in the Wake does not merely destroy, distort, or obscure meaningful patterns and structures but collaborates in their creation. The article is divided into three sections. First, I take two test cases from Ulysses and the Wake respectively, to show how noise is coded into meaning by both the waking and dreaming mind. Second, I examine the political dimensions of the imposition of meaning on noise and the subversions of meaning by noise in terms of the battle between generations (father against sons) and within generations (brother against brother). Finally, I place these themes in the context of the postmodernist

Acoustic detection and long-term monitoring of pygmy blue whales over the continental slope in southwest Australia

A 9-yr dataset of continuous sea noise recording made at the Cape Leeuwin station of the Comprehensive Nuclear-Test-Ban Treaty hydroacoustic network in 2002-2010 was processed to detect calls from pygmy blue whales and to analyze diurnal, seasonal, and interannual variations in their vocal activity. Because the conventional spectrogram correlation method for recognizing whale calls in sea noise resulted in a too high false detection rate, alternative algorithms were tested and the most robust one applied to the multi-year dataset. The detection method was based on multivariate classification using two spectrogram features of transients in sea noise and Fisher's linear discriminant, which provided a misclassification rate of approximately 1% for missed and false detections at moderate sensitivity settings. An analysis of the detection results revealed a consistent seasonal pattern in the whale presence and considerable interannual changes with a steady increase in the number of calls detected in 2002-2006. An apparent diurnal pattern of whales' vocal activity was also observed. The acoustic detection range for pygmy blue whales was estimated to vary from about 50 km to nearly 200 km from the Cape Leeuwin station, depending on the ambient noise level, source level, and azimuth to a vocalizing whale.

Underwater Noise Generated by a Small Ship in the Shallow Sea

Abstract Study of the sea noise has been a subject of interest for many years. The first works in this scope were published at the turn of the twentieth century by Knudsen (Knudsen et al., 1948) and G. Wenz (Wenz, 1962). Disturbances called “shipping noise” are one of the important components of the sea noise. In this work the results of an experimental research of underwater noise produced by a small ship of a classic propulsion are presented. A linear receiving antenna composed of two orthogonal components was used in the investigation. Identification of the main sources of acoustic waves related with the ship was achieved. In addition, the intensity of the wave was measured. The research was performed in conditions of the shallow sea.

Vector-scalar noise fields formed by an excited sea surface

Vector-scalar noise fields in a waveguide were studied using computer simulation. A stochastic model of dynamic acoustic noise was used in the calculations. Noise field parameters on a single vector-scalar module and spatial correlation functions on vector-scalar arrays in a homogeneous waveguide were analyzed. Calculations were performed for vertically and horizontally located arrays. It was shown that the vector-scalar noise field characteristics depend on the bottom parameters and the state of the ocean surface due to the wind force. The calculation results can be used to predict the characteristics of detection and direction finding of signal sources for vector-scalar arrays working in a waveguide against the background of sea noise.