Wind profiles measurements and predictions for atmospheric acoustic propagation modeling
The Journal of the Acoustical Society of America
This work presents a comprehensive experimental system to measure meteorological conditions with ... more This work presents a comprehensive experimental system to measure meteorological conditions with both anemometers and a three-dimensional scanning Doppler LIDAR wind profiler. The LIDAR system captures real-time wind speed gradients at many locations along a particular heading. This work describes a method for extracting a cartesian grid of wind speeds gradients from a range height indicator (RHI) scan pattern. The LIDAR derived wind profiles are compared to logarithmic wind profiles based on single point traditional anemometer measurements. Differences in wind speed profiles observed using the two methods are presented and the implications on long range acoustic propagation modeling are discussed.
Using machine learning to identify and assess cloud coverage
Journal of the Acoustical Society of America, Mar 1, 2023
Modeling sea state induced atmospheric sound transmission loss
The Journal of the Acoustical Society of America
This work presents a numerical study on atmospheric sound propagation over rough rigid surfaces. ... more This work presents a numerical study on atmospheric sound propagation over rough rigid surfaces. The intent is to simulate acoustic propagation over water. Methods to estimate sea state induced atmospheric sound transmission loss and relative uncertainties are evaluated. In previous studies, a flat surface with an equivalent impedance was used to account for the effect of surface roughness on sound transmission loss. Equivalent impedances were estimated based on time-domain numerical simulations of atmospheric sound propagation above pseudorandom sea surfaces coherent with a Pierson-Moskowitz spectra. Estimation of equivalent impedances using time- and frequency- domain approaches are compared for cases up to sea state 4. Acoustic excess attenuation due to propagation over a rough surface was predicted by the authors, in a previous work, by correcting the excess attenuation of a propagation over a flat, perfectly reflecting surface. The correction factor was frequency and sea state ...
Atmospheric acoustic propagation modeling using heterogeneous wind profiles along the acoustic path
The Journal of the Acoustical Society of America
This work presents atmospheric sound propagation predictions using a parabolic equation solver th... more This work presents atmospheric sound propagation predictions using a parabolic equation solver that accounts for heterogeneous wind profile distribution along the acoustic path. Transmission loss predictions using both homogeneous and heterogeneous wind speeds information are compared with data. A three-dimensional scanning Doppler LIDAR wind profiler captures real-time wind speed gradients at many locations along the acoustic propagation path providing the heterogeneous wind speed profiles. The wind measurements are concurrent with a pitch catch transmission loss measurements. A long-range acoustic device on an anchored pontoon sends known chirp sequences to a seven-channel receiver array at the water’s edge at ranges up to approximately one kilometer. Additional synchronized meteorological observations include temperature, humidity, and wind measured with anemometers. Key differences in model results are highlighted and an assessment of the value of the computational cost is prese...
Investigation of engineering models for sound propagation in a near-shore environment
The aim of the paper is to describe a portable, modular, and scaleable system for measuring concu... more The aim of the paper is to describe a portable, modular, and scaleable system for measuring concurrent acoustic transmission loss and atmospheric characteristics. This system has been developed specifically to inform an effort to improve the ability to implement high fidelity numerical predictions of acoustic transmission loss, particularly in acoustically complex outdoor ranges, such as those that occur in coastal areas. Such a system has broad possible applicability in many outdoor atmospheric acoustic monitoring scenarios.
Sea state induced sound transmission loss of atmospheric broadband sources
The Journal of the Acoustical Society of America
This work presents a numerical study conducted on atmospheric sound propagation over sea. In part... more This work presents a numerical study conducted on atmospheric sound propagation over sea. In particular, it focuses on the sound pressure level prediction uncertainties induced by the water surface roughness. To quantify these uncertainties, the generalized terrain parabolic equation (GTPE) is used to model sound propagation above water surfaces at different seastates. Water roughness is pseudo-randomly generated using Pierson-Moskovitz ocean wave spectrum. Building on a previous result that has established a simple expression for predicting single frequency sound transmission loss as a function of sea state, this work extends the approach to broadband signal from 125 to 1000 Hz. This work presents relationships between fully developed sea states (up to sea state 4) and the uncertainties on sound pressure level predictions at distances up to 1000 m from the source. These relationships are presented for typical nocturnal thermal gradients and for different elevations from the water s...
Experimental investigation of the variance of ground impedance measurments in coastal environments
The Journal of the Acoustical Society of America
The purpose of this work is to understand the results obtained with the ANSI/ASA S1.18 standard f... more The purpose of this work is to understand the results obtained with the ANSI/ASA S1.18 standard for outdoor acoustic surface impedance measurements when applied to surfaces with characteristics at or outside the recommended use case. This study is part of a larger effort working to develop a numerical model for long-range atmospheric acoustic transmission loss over coastal areas. Previous studies were done to characterize the relationship between moisture content and effective flow resistivity of sandy shores by conducting acoustic surface impedance measurements following the procedure specified in the ANSI/ASA S1.18. While the standard specifies surface variation of less than 5 cm and at least four measurements per location, this work seeks to understand the consequences of surface variation in natural terrains on the obtained results. These consequences were evaluated by measuring the effective flow resistivity of multiple outdoor surfaces such as uniform grass, raked sandy shores...
Estimation of atmospheric sound transmission loss due to sea roughness by mean of an effective impedance: A numerical validation
The Journal of the Acoustical Society of America, 2018
Preliminary numerical studies have been demonstrated that sea roughness introduces an excess of t... more Preliminary numerical studies have been demonstrated that sea roughness introduces an excess of transmission loss of atmospheric sound propagation. However, numerical solution of the parabolic equation that describes this phenomenon is computationally intensive, particularly when the spatial domain is large (>1 km). This study evaluates the validity of implementing an effective impedance (a flat absorbing surface) in the place of a rough surface. The effective impedance is a parametric complex quantity that is different for each sea state. The parameters of the impedance are estimated by best fitting the numerical solution of a two-dimensional finite-difference time-domain solver. The effectiveness and validity of using this impedance in place of a rough surface is evaluated by direct comparison of the solutions of the Crank-Nicolson parabolic equation obtained with and without the impedance.
On atmospheric humidity and acoustic ducts
The Journal of the Acoustical Society of America, 2018
The development of various propagation ducting phenomena (elevated or surface) has been studied e... more The development of various propagation ducting phenomena (elevated or surface) has been studied extensively for electromagnetic and electro-optical wave propagation. The influence of changes in temperature, pressure, and humidity gradients on the strength and geometry of the duct in the electromagnetic propagation problem is well-documented, and there is substantial literature regarding the influence of temperature gradient on atmospheric acoustic propagation. Analytical results indicate that moisture gradients in warm air above a sea surface contribute meaningfully to the refraction of sound. This work uses numerical simulation to explore the atmospheric conditions that would support development of acoustic ducts or wave guide conditions during moderate range (<1 km) acoustic propagation. The aim of this overall effort is an improved numerical model of acoustic refraction and attenuation over moderate to long distances above a sea surface that accounts for sea state as well as b...
Full-field laser vibrometer study of dissipation in a beam with a coupled oscillator array
The Journal of the Acoustical Society of America, 2017
Coupled oscillator systems can be designed to manage the distribution of mechanical energy in vib... more Coupled oscillator systems can be designed to manage the distribution of mechanical energy in vibration or acoustic systems. A specific implementation of an array composed of small damped mass-spring attachments on a primary is here referred to as a subordinate oscillator array. SOAs and their ability to absorb energy from a primary mass are of continued importance in analysis for both structural and acoustic systems. The ability to dissipate energy in a specific frequency band has many potential applications. This work will use laser Doppler vibrometry (LDV) to evaluate a beam mounted on an electromechanical shaker with and without an attached planar SOA composed of much smaller beams. This study is motivated by earlier work that indicated a high sensitivity to disorder in the form of fabrication error. The apparatus allows for the controlled introduction of various levels of disorder to quantify its effect and compare to a numerical model. We will show full-field forced response f...
Sea surface contribution to sound transmission loss: Numerical comparison between three-dimensional and cylindrical symmetry approximation solutions
The Journal of the Acoustical Society of America, 2018
The atmospheric sound propagation over the sea depends on several factors including but not limit... more The atmospheric sound propagation over the sea depends on several factors including but not limited to temperature, wind speed, relative humidity, and roughness of the surface. The objective of this study is to determine the contribution to sound transmission loss of the sea surface roughness. The governing equations are implemented for a three-dimensional domain using a finite element method solver. The sea surface is assumed to be perfectly reflective and its shape is pseudo-randomly generated by using the Pierson and Moskowitz model. In previous studies, the cylindrical symmetry approximation has been widely used to allow a fast computation of the equations. However, the implementation of a three-dimensional domain allows a more realistic scenario and is here used as a tool to quantify the deviation from the approximated solution. An appropriate correction factor to be used when applying the cylindrical symmetry approximation is determined.
This work presents an effort to understand and characterize the role moisture content plays in ho... more This work presents an effort to understand and characterize the role moisture content plays in how sound interacts with sand on the beach. This exploratory effort is part of a larger project developing a numerical model of long-range (up to approximately 3 km) atmospheric acoustic propagation in littoral or riverine environments with a near-shore acoustic source and on-shore receivers. Previous experiments have studied moisture content of sand samples taken at various distances from the water's edge of an artificial beach. This works seeks to perform the same studies in natural coastal areas by recording moisture content in situ via a moisture probe at two depths and conducting testing with an impedance tube. Samples are collected at several distances from the shoreline at high and low tides. The results collected at the natural coastal areas are compared to those obtained from studies at the artificial lake in order to inform a related effort that seeks to capture the acoustic characteristics of the sandy beach for use in numerical modeling efforts. This study shows essentially no tidal influence on beach moisture gradient. The observed distance over which the sand transitioned from saturated to dry was generally less than a few meters.
Acoustic transmission loss models using experimental temperature profiles of the near surface atmospheric boundary layer
This work presents a comparison between existing simple atmospheric temperature models and experi... more This work presents a comparison between existing simple atmospheric temperature models and experimental measurements of the lower atmospheric boundary layer. This work is part of a larger project developing an improved numerical model of atmospheric acoustic propagation in littoral or riverine environments with a near-shore acoustic source and on-shore receivers. In this study, temperature, humidity, and pressure data are collected with the use of sensors mounted on an unmanned aerial vehicle. Vertical measured temperature profiles are compared to existing common models and assumptions to gain a better understanding of how sufficient these models are at representing the meteorological parameters that will affect acoustic transmission. Representative transmission loss case studies comparing measured and model temperature profiles are included. Temperature profiles that do not represent the observed very near surface warming present in the case study lead to predicted transmission los...
Earlier work has shown that an array of very small attached resonators can be designed to alter t... more Earlier work has shown that an array of very small attached resonators can be designed to alter the dynamic response of a primary structure. The altered response can be designed to make the primary structure appear heavily damped or to have a particular spectral shape such as a bandpass response. However, small errors in the distribution of mass and stiffness distribution of the attachments can have a significant effect, degrading the intended performance. This presentation discusses a concept of correcting small property distribution errors using shunted piezoelectric strip actuators bonded to the attachments.
Atmospheric sound transmission loss uncertainties induced by sea roughness
The Journal of the Acoustical Society of America, 2021
This work presents a numerical study conducted on atmospheric sound propagation over sea. In part... more This work presents a numerical study conducted on atmospheric sound propagation over sea. In particular, it focuses on the sound pressure level prediction uncertainties induced by the water surface roughness. To quantify these uncertainties, the generalized terrain parabolic equation (GTPE) is used to model sound propagation above water surfaces at different sea states. Water roughness is pseudo-randomly generated using an ocean wave spectrum. The GTPE predictions are compared with those obtained using the Crank-Nicholson parabolic equation (CNPE) solver. When using the CNPE the sea surface is flat and has a surface impedance equivalent to that of a rough surface. The use of the GTPE is less computationally efficient but provides insight on the detectability of an acoustic source at sea. This work presents relationships between fully developed sea states (up to sea state 4) and the uncertainties on sound pressure level predictions at distances up to 500 m from the source. These rela...
Acoustic surface impedance of sandy shores
The Journal of the Acoustical Society of America, 2021
This work presents an effort to characterize the relationship between moisture content and acoust... more This work presents an effort to characterize the relationship between moisture content and acoustic surface impedance of sandy soils. This effort is part of a larger project seeking to model long-range acoustic transmission loss over coastal areas. Previous studies were done to measure moisture content along the shore and collect samples for bench-testing with an impedance tube. This work seeks to build on those experiments by performing in situ acoustic surface impedance measurements with an omnidirectional sound source and two microphone receivers. These measurements follow the protocol set forth by the ANSI/ASA S1.18 and are recorded at multiple distances from the water on the shore. At each measurement location, sand samples are collected for gravimetric moisture analysis. Atmospheric conditions and ambient noise level are also recorded in accordance with the standard. These results demonstrate the variation of sand surface impedance from the fully saturated swash zone to nomina...
Graduate study at the Catholic University of America: Towards a century of acoustics
The Journal of the Acoustical Society of America, 2020
The Catholic University of America (CUA) has a graduate program with a long history in acoustics ... more The Catholic University of America (CUA) has a graduate program with a long history in acoustics dating back to the early 1930s. The acoustics program moved to the School of Engineering in the 1960s when there were strong needs in underwater acoustic studies to meet U.S. Naval applications. Recent interests include acoustical engineering, acoustic metamaterials, and environmental acoustic. Currently, a variety of graduate level acoustic courses are being offered in the CUA's Mechanical Engineering Department. Students can pursue a MS in Mechanical Engineering or Ph.D. with research in acoustics or vibrations. The courses in the program include a two-course sequence in fundamentals of acoustics, and more focused courses in ocean acoustics, atmospheric acoustics, acoustic metrology, marine bioacoustics, nonlinear vibration, acoustic imaging, and acoustic metamaterials. In addition, this program enables working professionals in the Washington, DC, area to complete a graduate degree...
Excess attenuation at the beach: A model validation
The Journal of the Acoustical Society of America, 2020
This work presents a comparison between experimental results and numerical modeling of atmospheri... more This work presents a comparison between experimental results and numerical modeling of atmospheric sound transmission loss across a range that includes water and a sandy shore. This work is part of a larger project developing a numerical model of long-range (∼3 km) atmospheric acoustic propagation in littoral or riverine environments with a near-shore acoustic source and on-shore receivers. The narrow angle parabolic equation method used in this work accounts for wind and temperature variation with elevation along the acoustic propagation path. The beach is modelled as an equivalent fluid employing the Johnson-Champoux-Allard-Pride-Lafarge (JCAPL) model. This eight-parameters model is reduced to a one-parameter model by considering the sand as randomly packed spherical particles. The single parameter is the grain size. Measured grain size distributions of the sand and its change in water content with the distance from the water inform model development of the beach. Sound pressure l...
Comparison of existing and experimental weather models of the near surface atmospheric boundary layer
The Journal of the Acoustical Society of America, 2020
This work presents a comparison between existing weather models and experimental measurements of ... more This work presents a comparison between existing weather models and experimental measurements of the lower atmospheric boundary layer. This work is part of a larger project developing a numerical model of long-range (~3 km) atmospheric acoustic propagation in littoral or riverine environments with a near-shore acoustic source and on-shore receivers. Temperature, humidity, and pressure data are collected with the use of iMet-XQ2 sensors mounted on an unmanned aerial vehicle. Vertical measured profiles that will then be compared to existing common models and assumptions (such as Monin-Obukhov similarity theory) to gain a better understanding of these mathematical models and how sufficient these models are at representing the meteorological parameters that will affect acoustic transmission.
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