Ambient Noise Power Research Articles

Signal detection method using a single vector hydrophone in ocean acoustics.

This paper focuses on the problem of transient signal detection using a single vector hydrophone in a horizontal isotropic acoustic field. The covariance matrix of the three sensor output quantities is analyzed in terms of its trace and determinant principal invariants, and the mathematical relationship between the signal-to-noise ratio and these invariants is established. Both the signal power and the ambient-noise power can be accurately estimated directly from the covariance matrix of the received data, and the signal-to-noise ratio can further be obtained. A signal power detector is proposed based on the theoretical analysis, and simulation results show that (i) it can detect signals with low signal-to-noise ratio and (ii) its performance is greatly improved compared with that of an energy detector under the condition of a nonstationary ambient-noise field. An experiment was performed to verify the theoretical analysis and the conclusions of the numerical simulation, and the data-processing results show that this method has good applicability in signal detection.

Empirical mapping for evaluating an LPWAN (LoRa) wireless network sensor prior to installation in a vineyard

The main aim of this study was to use Empirical mapping to test the efficiency of local low cost wireless network sensors (LPWAN - Low-Power Wide Area Network) before being applied in real wine-growing conditions. The second aim was to obtain information on the communication distances to be expected from a LPWAN, taking into account the specific needs and real conditions of a vineyard. A hand-held autonomous end-device was specifically built to simulate short messages sent by sensors via a locally designed LPWAN. This device was used to test the quality of the network from different locations within an entire vineyard and also inside the cellar. Two parameters were used to test the quality of reception of the messages: i) The Received Signal Strength Indication (RSSI), which is the received signal power measured in decibels (dB or dBm), and ii) the Signal-to-Noise Ratio (SNR), which is the ratio of the received signal power to the ambient noise power. Maps of signal reception and errors between the observed and the theoretical signal highlighted how vineyard environment (e.g., hedges, topography, and buildings) affects the signal. The results show that the maximum communication distance differed considerably from distances published in the literature. In the open field, the signal, although attenuated by the distance, was received up to 600 meters away, or even more in favourable conditions. Meanwhile, in urban areas the signal was attenuated by buildings and the electro-magnetic environment and therefore communication distances were very short (< 50 m). Empirical mapping has great potential for determining how the local environment affects signal quality and as a decision support tool for identifying the optimal location for the sensors and gateway. With a single well-positioned gateway, such low cost wireless sensor networks (LPWAN-LoRa) could be used by small to medium-sized vineyards to collect information from sensors either outside in the fields or indoors in the vineyard cellar. This paper proposes a very cheap method (< 40 €) for testing and spatialising the quality of a low cost wireless sensor network before its implementation, and it also provides information on zones with low quality reception.

Local acoustic habitat relative to hearing sensitivities in beluga whales (Delphinapterus leucas)

Background noise can have a substantial effect on communication signals, however far less is known about how natural soundscapes may influence hearing sensitivity. Here we compare the audiograms of 26 wild beluga whales measured in their natural environment to a series of ecoacoustic measurements within a primary portion of their Bristol Bay summer habitat, the Nushagak Estuary in Bristol Bay, AK, USA. Environmental acoustic measurements were made during 2012 and 2016 using two different methods: a moored recorder and drifter buoys. Environmental noise curves varied substantially. Drifter recordings from the middle of Nushgak Estuary had the highest spectrum levels during ebb tides with acoustic energy from sediment transport extending well into higher frequencies (ca. 60 kHz), likely due to rapidly moving tidal flow and shifting sediment in that location. Drifter recordings near the estuary mouth and shallow tidal flats were lower amplitude. Noise levels generally varied during drifts (in one case up to ca. 6 dB) reflecting acoustic cues available to the local belugas. The moored recorder showed a substantially different spectral profile, especially at lower frequencies, perhaps due to its attachment to a pier piling and subsequent pier noise. Hearing sensitivity varied by individual and thresholds often fell above 1/3 octave-band noise levels, but not overall noise spectral density. Audiograms of the most sensitive animals closely paralleled the lowest ambient noise power spectral density curves, suggesting that an animal’s auditory dynamic range may extend to include its habitat’s quietest conditions. These data suggest a cautious approach is necessary when estimating the sound-sensitivity of odontocetes found in quiet environments as they may have sensitive auditory abilities that allow for hearing within the lowest noise-level conditions. Further, lower level ambient noise conditions could provide a conservative estimate of the maximal sensitivity of some cetacean populations within specific environments.

A Speech Distortion and Interference Rejection Constraint Beamformer

Signals captured by a set of microphones in a speech communication system are mixtures of desired and undesired signals and ambient noise. Existing beamformers can be divided into those that preserve or distort the desired signal. Beamformers that preserve the desired signal are, for example, the linearly constrained minimum variance (LCMV) beamformer that is supposed, ideally, to reject the undesired signal and reduce the ambient noise power, and the minimum variance distortionless response (MVDR) beamformer that reduces the interference-plus-noise power. The multichannel Wiener filter, on the other hand, reduces the interference-plus-noise power without preserving the desired signal. In this paper, a speech distortion and interference rejection constraint (SDIRC) beamformer is derived that minimizes the ambient noise power subject to specific constraints that allow a tradeoff between speech distortion and interference-plus-noise reduction on the one hand, and undesired signal and ambient noise reductions on the other hand. Closed-form expressions for the performance measures of the SDIRC beamformer are derived and the relations to the aforementioned beamformers are derived. The performance evaluation demonstrates the tradeoffs that can be made using the SDIRC beamformer.

Interference Identification for Next Generation Wireless Networks

With the huge success of cellular mobile radio communications, demand for wireless services, applications, and technologies is expected to increase further. Such an increase forces recently emerging technologies (e.g., 4G) to coexist with the old ones (e.g., 2G–3G) in next generation wireless networks (NGWNs). In order for NGWNs to support all of these services and applications with the ever-increasing demand, wireless radio interference needs to be handled in an effective manner. Interference is a phenomenon which degrades the overall system capacity, affects the quality of service, and causes call drops and unnecessary handoffs in cellular mobile systems. Interference is a very important concept from the perspective of military and of national security. Both unintentional and intentional interference, which is also known as jamming, should be cleared away as soon as possible for security reasons. Therefore, identification of interference in a reliable manner is a crucial task for all of the future wireless communications systems. In this study, identification of radio interference in NGWNs is established. The proposed method takes into account the general characteristics of wireless propagation environments. Since it is difficult to completely define a general wireless propagation environment, statistical properties of widely used propagation environment classification such as urban and suburban is analyzed. Both first- and second-order of the statistical characteristics of wireless propagation environments are considered. It is shown that the proposed method can identify the presence of interference under practical scenarios in a reliable manner. In addition, it is demonstrated that the absence of a priori knowledge about the ambient noise power does not affect the performance of the proposed method. Interference management is predicted to be an essential part of the system design for emerging NGWNs. Interference is also extremely important for military and national security applications and services. Therefore, identification of any form of interference in a reliable manner is of crucial importance. In this study, a method that can identify the presence of interference reliably under practical scenarios is proposed. The method proposed does need any a priori information to identify the interference.

Maximizing the data transmission rate of a cooperative relay system in an underwater acoustic channel

In this paper, we investigate the problem of maximizing the data transmission rate of a cooperative relay system in an underwater acoustic communication channel. With amplify-and-forward relaying and adaptive source transmission, we present optimal transmit signal power adaptation policies that maximize the data transmission rate, considering both frequency and time domains. The analysis takes into account a physical model of acoustic path loss and ambient noise power spectral density. Typical characteristics of underwater channel such as frequency-dependent fading and time variations are also considered. Capacity bounds for channel state information (CSI) only at the receiver and CSI at both transmitter and receiver are presented. To maximize the data rate, we use the notion of an optimal bandwidth which corresponds to efficient allocation of signal power across the transmission bandwidth. Under the constraint of an average transmit power, the optimal transmit power adaptation policy is found to be ‘water-pouring’ in frequency-time domain, while the transmit power adaptation policy with a total power constraint is ‘water-pouring’ in frequency domain. Results show that both frequency domain and frequency-time domain power adaptation schemes provide much greater improvement in average data rate over that of the constant power case. Copyright © 2011 John Wiley & Sons, Ltd.

Capacity of Underwater Wireless Communication Channel With Different Acoustic Propagation Loss Models

In this paper, we calculate the capacity of a point-to-point communication link in an underwater acoustic channel. The analysis takes into account the effects of various acoustic propagation loss models. A physical model of ambient noise power spectral density is also considered. We perform a comparative assessment of the influence of various acoustic transmission loss models on the acoustic bandwidth and the capacity.

Temporal Variations in Global Seismic Station Ambient Noise Power Levels

Research Article| July 01, 2010 Temporal Variations in Global Seismic Station Ambient Noise Power Levels A. T. Ringler; A. T. Ringler U.S. Geological Survey Albuquerque Seismological Laboratory P.O. Box 82010 Albuquerque, New Mexico 87198-2010 U.S.A. aringler@usgs.gov Search for other works by this author on: GSW Google Scholar L. S. Gee; L. S. Gee U.S. Geological Survey Albuquerque Seismological Laboratory P.O. Box 82010 Albuquerque, New Mexico 87198-2010 U.S.A. aringler@usgs.gov Search for other works by this author on: GSW Google Scholar C. R. Hutt; C. R. Hutt U.S. Geological Survey Albuquerque Seismological Laboratory P.O. Box 82010 Albuquerque, New Mexico 87198-2010 U.S.A. aringler@usgs.gov Search for other works by this author on: GSW Google Scholar D. E. McNamara D. E. McNamara Search for other works by this author on: GSW Google Scholar Author and Article Information A. T. Ringler U.S. Geological Survey Albuquerque Seismological Laboratory P.O. Box 82010 Albuquerque, New Mexico 87198-2010 U.S.A. aringler@usgs.gov L. S. Gee U.S. Geological Survey Albuquerque Seismological Laboratory P.O. Box 82010 Albuquerque, New Mexico 87198-2010 U.S.A. aringler@usgs.gov C. R. Hutt U.S. Geological Survey Albuquerque Seismological Laboratory P.O. Box 82010 Albuquerque, New Mexico 87198-2010 U.S.A. aringler@usgs.gov D. E. McNamara Publisher: Seismological Society of America First Online: 09 Mar 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2010 by the Seismological Society of America Seismological Research Letters (2010) 81 (4): 605–613. https://doi.org/10.1785/gssrl.81.4.605 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. T. Ringler, L. S. Gee, C. R. Hutt, D. E. McNamara; Temporal Variations in Global Seismic Station Ambient Noise Power Levels. Seismological Research Letters 2010;; 81 (4): 605–613. doi: https://doi.org/10.1785/gssrl.81.4.605 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Recent concerns about time-dependent response changes in broadband seismometers have motivated the need for methods to monitor sensor health at Global Seismographic Network (GSN) stations. We present two new methods for monitoring temporal changes in data quality and instrument response transfer functions that are independent of Earth seismic velocity and attenuation models by comparing power levels against different baseline values. Our methods can resolve changes in both horizontal and vertical components in a broad range of periods (∼0.05 to 1,000 seconds) in near real time. In this report, we compare our methods with existing techniques and demonstrate how to resolve... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Imaging in the ocean with ambient noise: the ORB experiments

Acoustic daylight imaging is a new technique that has been proposed for creating pictorial images of objects in the ocean from the ensonification provided by the incident ambient noise field. To investigate the feasibility of the technique, a series of experiments was performed from the research platform ORB, moored in San Diego Bay, Southern California. Central to these experiments was an acoustic receiver known as ADONIS (acoustic daylight ocean noise imaging system), which consists of a spherical reflector, 3 m in diameter, with an elliptical array of 130 hydrophones at the focal surface. This system, which is broadband, operating between 8 and 80 kHz, forms a total of 126 receive-only beams spanning the vertical and horizontal. The ambient noise power in each beam is mapped into a pixel on a VDU. Various types of targets were used in the experiments, including planar panels and cylindrical, polyethylene drums containing wet sand, seawater or syntactic foam (essentially air), and most of the experiments were conducted with the targets at ranges between 20 and 40 m. At the time of the experiments the noise field in the area was created primarily by snapping shrimp. Moving, color images of the object space were successfully created with ADONIS. Some representative static images from the moving sequences are presented and discussed in the paper.

Infrasonic ambient noise in the ocean due to atmospheric pressure fluctuations on the surface

The theory of infrasonic ambient noise in a semiinfinite, isotropic ocean due to random wind-pressure fluctuations acting on the sea surface is reexamined. The surface pressure field is modeled as a Poisson distribution of point forces. This provides a boundary condition that must be satisfied by the solution of the homogeneous Helmholtz equation for the resultant acoustic field in the ocean. Using this solution the spatial coherence function of the ambient noise is constructed, from which the directionality in the vertical is derived and shown to be the same as that for the noise field produced by a random distribution of vertical dipoles on the surface. The power spectrum of the noise scales with the point spectrum of the wind-pressure fluctuations, which is determined empirically from published measurements of wind-pressure spectra taken over water, and with the square of the Helmholtz number for the turbulent sources. Since the Helmholtz number is very much less than unity, it is concluded that wind turbulence is an inefficient mechanism for producing sound in the ocean. A comparison of the final result for the ambient noise power spectrum with measured noise spectra, taken by several investigators in various parts of the world, indicates that wind turbulence generally makes an insignificant contribution to the infrasonic ambient noise in the ocean.

In situ acoustic calibration for a large aperture array

During September 1987, a large aperture acoustic array was deployed vertically in the Northeast Pacific to study low-frequency noise in the ocean. Coherent combination of the 120-channel outputs requires knowledge of individual element amplitude and phase response for accurate results. Two in situ methods of array calibration are described and results from the September experiment are presented. The first method used transmissions from a low-frequency source of known location and power level. Simulating the conditions encountered during the transmission, the power arriving at the array was predicted by several acoustic propagation models. By comparing the array response at specific frequencies to the response predicted by the models, an absolute calibration was obtained. An error curve for the phase data was generated by unwrapping the phase, accounting for a sampling offset in the array, and subtracting a multiple linear regression curve. The second method determines relative amplitude levels by examining the average ambient noise power output of a specified frequency band across the array. Using spectral, coherence, and directionality plots, the level of self-noise in the array was shown to be below that of the ambient noise being measured. These two independent methods provide a consistent set of element calibration values used for array beamforming. [Work supported by ONT.]

Suppression of acoustic noise in speech using two microphone adaptive noise cancellation

Acoustic noise with energy greater or equal to the speech can be suppressed by adaptively filtering a separately recorded correlated version of the noise signal and subtracting it from the speech waveform. It is shown that for this application of adaptive noise cancellation, large filter lengths are required to account for a highly reverberant recording environment and that there is a direct relation between filter misadjustment and induced echo in the output speech. The second reference noise signal is adaptively filtered using the least mean squares, LMS, and the lattice gradient algorithms. These two approaches are compared in terms of degree of noise power reduction, algorithm convergence time, and degree of speech enhancement. Both methods were shown to reduce ambient noise power by at least 20 dB with minimal speech distortion and thus to be potentially powerful as noise suppression preprocessors for voice communication in severe noise environments.

Approximate ray angle diagram

The ray angle diagram presents loci as a function of depth of the angles which selected rays make with the horizontal as sound propagates in the ocean. It provides useful qualitative information about deep ocean propagation and the vertical distribution of signal and ambient noise power. The loci are based on Snell’s law. It is shown that an approximate ray angle diagram (ARAD) can be easily constructed directly from the sound-velocity profile since on an appropriate scale the loci of one minus the cosine of the ray angle versus depth are approximately mirror images of the sound-velocity profile. The approximations are shown to involve negligible errors for cases of interest in underwater acoustics. The use and construction of the ARAD are illustrated with examples. A simple graphical technique is presented for annotating the ARAD with range information from which rays may be plotted without the use of a computer.

Approximate ray angle diagram

The Ray Angle Diagram presents loci as a function of depth of the angles which selected rays make with the horizontal as sound propagates in the ocean. It provides useful qualitative information about deep ocean propagation and the vertical distribution of signal and ambient noise power. The loci are based on Snell's law. It is shown that an Approximate Ray Angle Diagram (ARAD) can be easily constructed directly from the Sound Velocity Profile since on an appropriate scale the loci of one minus the cosine of the ray angle versus depth are approximately mirror images of the Sound Velocity Profile. The approximations are shown to involve negligible errors for cases of interest in underwater acoustics. The use and construction of the ARAD are illustrated with examples. A simple graphical technique is presented for annotating the ARAD with range information from which rays may be plotted without the use of a computer.

COLLECTION AND ANALYSIS OF PACIFIC OCEAN‐BOTTOM SEISMIC DATA

A total of 500 hours of usable ocean‐bottom seismic data recorded on pressure and three components of velocity has been collected in three geographically separate areas of the Pacific Ocean at depths to 20,000 ft. These data are presently being analyzed to determine the extent to which monitoring seismic motion on the ocean floor can assist Project VELA UNIFORM goals of detection and identification of underground and underwater nuclear blasts. Analysis of three earthquakes and ambient noise recorded simultaneously on the ocean bottom and land reveals: 1. Ocean‐bottom signal‐to‐noise ratios are equal to or less than those seen at a comparative land station; 2. Ocean‐bottom signal and noise levels are higher than those obtained at the land station; and 3. Ocean‐bottom ambient noise power spectra increase in level towards the microseismic 6‐ to 8‐sec peak as do the land data. No strong directional ocean‐bottom noise components have been observed. Simultaneous recording of pressure and particle velocity affords the ocean‐bottom station a distinct advantage over its land counterpart, through exploitation of the relationships between pressure and vertical velocity which exist for various types of arrivals and modes.