Surface Wave Measurements Research Articles

Vertical seismic profiling using double-beamforming processing of nonuniform anthropogenic seismic noise: The case study of Rittershoffen, Upper Rhine Graben, France

Correlating ambient seismic noise allows us to image the subsoil in various contexts and at different scales. Applying this technique to anthropogenic seismic noise can be challenging when the spatial distribution of the sources is not uniform. We have addressed the feasibility of exploiting this kind of noise in addition to microseismic noise to extend the reconstruction of Rayleigh-wave dispersion at periods between 0.2 and 1 s. We used data acquired with two small aperture arrays ([Formula: see text] stations with a 200 m helical distribution) deployed near the deep geothermal site of Rittershoffen (Alsace, France). In this region, the sparse human activity causes strong seismic noise, whose nonuniform spatial distribution limits our ability to determine the surface wave velocity between stations using the classical noise correlation technique at periods of less than 1 s. We have used double beamforming to isolate the noise sources that contribute constructively to the empirical Green’s function between the two arrays and recovered the Rayleigh-wave dispersion curve at periods less than 1 s. Using a probabilistic inversion, we found that such data, combined with surface wave measurements at periods greater than 1 s, are helpful to improve the reliability of [Formula: see text] and [Formula: see text] profiles at depths down to the deep-geothermal reservoir (2.5 km). Such profiles are helpful in a geothermal context because they improve the location of induced seismic events, necessary for reservoir monitoring and risk assessment.

GSpecDisp: A matlab GUI package for phase-velocity dispersion measurements from ambient-noise correlations

We present a graphical user interface (GUI) package to facilitate phase-velocity dispersion measurements of surface waves in noise-correlation traces. The package, called GSpecDisp, provides an interactive environment for the measurements and presentation of the results. The selection of a dispersion curve can be done automatically or manually within the package. The data are time-domain cross-correlations in SAC format, but GSpecDisp measures phase velocity in the spectral domain. Two types of phase-velocity dispersion measurements can be carried out with GSpecDisp; (1) average velocity of a region, and (2) single-pair phase velocity. Both measurements are done by matching the real part of the cross-correlation spectrum with the appropriate Bessel function. Advantages of these two types of measurements are that no prior knowledge about surface-wave dispersion in the region is needed, and that phase velocity can be measured up to that period for which the inter-station distance corresponds to one wavelength. GSpecDisp can measure the phase velocity of Rayleigh and Love waves from all possible components of the noise correlation tensor. First, we briefly present the theory behind the methods that are used, and then describe different modules of the package. Finally, we validate the developed algorithms by applying them to synthetic and real data, and by comparison with other methods. The source code of GSpecDisp can be downloaded from: https://github.com/Hamzeh-Sadeghi/GSpecDisp.

Susy, Seascan, and other acoustical contraptions

In the early 1990s, the acoustical oceanography research group, led by Dr. David Farmer, developed several high-frequency sonar platforms for near-surface oceanography. These platforms, suspended approximately 25 m below the surface, typically supported six frequencies of upward-looking echo-sounders and up to four steerable 100 kHz sidescan sonars. Additionally, the SUSY platform had four extensible arms, 4.5 m in length, each supporting a wideband hydrophone. The platforms had sufficient batteries and data recording for up to 40 hours of autonomous operation, which could be extended through scheduled on/off periods. The intent of these platforms was to investigate properties of near-surface bubble due to breaking waves, with additional Doppler velocity measurements of surface waves and convective circulations. These platforms were also used for other studies, such as tidal convergence zones and ship wakes. The SEACAN platform was also used to assess zooplankton and fish populations in lake in Japan. This presentation will review key field trials and scientific achievements generated through use of these platforms.

Acoustic surface waves measurements by self mixing array transducers for nondestructive testing and structure health monitoring applications

In the Non Destructive Testing (NDT) and Structure Health Monitoring (SHM) field, Surface Acoustic Waves (SAWs) are widely employed to detect defects and/ or to monitor the integrity of the structure to test. In this context, SAWs contactless measurements offer several advantages with respect to the traditional use of a recording piezoelectric transducers fixed in the structure to test. They can be easily employed in situations of difficult access to the structure avoiding the generation of undesired reflections due to the presence of a second transducers mass. The gold standard technique for this this kind of measurements is the scanning Laser Doppler Vibrometer (sLDV), which allows to perform contactless measurements with a high spatial resolutions and a good Signal to Noise ratio. The main drawback is the high costs to be supported and the large acquisition time that a 2D grid of measurement points could require. Moreover, to ensure an optimal reflection of the incident light, the surface of the structure under test is often treated with reflective paint or stickers. The purpose of this article is to build a large bandwidth array transducer for NDT/SHM applications overcoming the sLDV measurements disadvantages. This technique is based on the use of Laser diodes. The principle behind this approach is the Self Mixing effect occurring when the optical beam is back-scattered in the active cavity of the diode itself.

Assessment of a geological model by surface wave analyses

A set of horizontal to vertical spectral ratio (HVSR) and multichannel analysis of surface waves (MASW) measurements, carried out in the Altavilla Milicia (Sicily) area, is analyzed to test a geological model of the area. Statistical techniques have been used in different stages of the data analysis, to optimize the reliability of the information extracted from geophysical measurements. In particular, cluster analysis algorithms have been implemented to select the time windows of the microseismic signal to be used for calculating the spectral ratio H/V and to identify sets of spectral ratio peaks likely caused by the same underground structures. Using results of reflection seismic lines, typical values of P-wave and S-wave velocity were estimated for each geological formation present in the area. These were used to narrow down the research space of parameters for the HVSR interpretation. MASW profiles have been carried out close to each HVSR measuring point, provided the parameters of the shallower layers for the HVSR models. MASW inversion has been constrained by extrapolating thicknesses from a known stratigraphic sequence. Preliminary 1D seismic models were obtained by adding deeper layers to models that resulted from MASW inversion. These justify the peaks of the HVSR curves due to layers deeper than MASW investigation depth. Furthermore, much deeper layers were included in the HVSR model, as suggested by geological setting and stratigraphic sequence. This choice was made considering that these latter layers do not generate other HVSR peaks and do not significantly affect the misfit. The starting models have been used to limit the starting research space for a more accurate interpretation, made considering the noise as a superposition of Rayleigh and Love waves. Results allowed to recognize four main seismic layers and to associate them to the main stratigraphic successions. The lateral correlation of seismic velocity models, joined with tectonic evidences, allowed to plot two geological sections, showing the main pattern of geological formations and tectonic structures.

Implementation of S-band marine radar for surface wave measurement under precipitation

Civil marine radar, which operates at a low grazing-incidence angle and with horizontal polarization in transmitting and receiving, can be modified and used as a primary tool for surface wave monitoring. The high spatial resolutions of sea-clutter image sequences from X-band radar offer a means of deriving individual waves and wave field at low-cost. However, the performance of X-band radar is impaired under rainy conditions, which are usually accompanied by the severe weather at sea. In the present study, we examine the effectiveness of S-band radar for wave measurements under precipitation. The results of comprehensive comparative studies with sea-truth data show that S-band radar is capable of carrying out wave measurements in rainy conditions. Although the longer wavelength of the S-band leads to a coarser resolution of radar imagery, the S-band radar features at least the equivalent performance of the X-band system in non-rainy conditions, in terms of wave height measurement. The results suggest that the S-band and X-band could be complementary systems. In rainy conditions the S-band is more efficient but in the non-rainy periods the X-band gives more confident results. The relationship of significant wave height with radar signal-to-noise ratio (SNR), and the modulation transfer function (MTF) between radar spectrum and wave spectrum for the used X-band and S-band radars are established and discussed in this paper.

A contactless ultrasonic surface wave approach to characterize distributed cracking damage in concrete

We describe an approach that utilizes ultrasonic surface wave backscatter measurements to characterize the volume content of relatively small distributed defects (microcrack networks) in concrete. A simplified weak scattering model is used to demonstrate that the scattered wave field projected in the direction of the surface wave propagation is relatively insensitive to scatterers that are smaller than the propagating wavelength, while the scattered field projected in the opposite direction is more sensitive to sub-wavelength scatterers. Distributed microcracks in the concrete serve as the small scatterers that interact with a propagating surface wave. Data from a finite element simulation were used to demonstrate the viability of the proposed approach, and also to optimize a testing configuration to collect data. Simulations were validated through experimental measurements of ultrasonic backscattered surface waves from test samples of concrete constructed with different concentrations of fiber filler (0.0, 0.3 and 0.6%) to mimic increasing microcrack volume density and then samples with actual cracking induced by controlled thermal cycles. A surface wave was induced in the concrete samples by a 50kHz ultrasonic source operating 10mm above the surface at an angle of incidence of 9°. Silicon-based miniature MEMS acoustic sensors located a few millimeters above the concrete surface both behind and in front of the sender were used to detect leaky ultrasonic surface waves emanating from concrete. A normalized backscattered energy parameter was calculated from the signals. Statistically significant differences in the normalized backscattered energy were observed between concrete samples with varying levels of simulated and actual cracking damage volume.

Field and laboratory stress-wave measurements of asphalt concrete

Non-contact surface wave measurements are performed on a new asphalt concrete (AC) pavement using 48 micro-electro-mechanical system (MEMS) sensors as receivers to estimate the real part of the dynamic moduli of the AC top layer. Laboratory measurements of core samples, extracted from the field measurement positions, are used to construct master curves for comparison with the field measurements. The real parts of the dynamic moduli from the two test methods are consistent at the field measurement temperatures, and the non-contact field measurements are highly repeatable. These results indicate a possible application for quality assurance of AC based on mechanical properties.

Convertion Shear Wave Velocity to Standard Penetration Resistance

Multichannel Analysis Surface Wave (MASW) measurement is one of the geophysics exploration techniques to determine the soil profile based on shear wave velocity. Meanwhile, borehole intrusive technique identifies the changes of soil layer based on soil penetration resistance, i.e. standard penetration test-number of blows (SPT-N). Researchers across the world introduced many empirical conversions of standard penetration test blow number of borehole data to shear wave velocity or vice versa. This is because geophysics test is a non-destructive and relatively fast assessment, and thus should be promoted to compliment the site investigation work. These empirical conversions of shear wave velocity to SPT-N blow can be utilised, and thus suitable geotechnical parameters for design purposes can be achieved. This study has demonstrated the conversion between MASW and SPT-N value. The study was conducted at the university campus and Sejagung Sri Medan. The MASW seismic profiles at the University campus test site and Sejagung were at a depth of 21 m and 13 m, respectively. The shear wave velocities were also calculated empirically using SPT-N value, and thus both calculated and measured shear wave velocities were compared. It is essential to note that the MASW test and empirical conversion always underestimate the actual shear wave velocity of hard layer or rock due to the effect of soil properties on the upper layer.

A noninvasive ultrasound elastography technique for measuring surface waves on the lung

The purpose of this work was to demonstrate an ultrasound based surface wave elastography (SWE) technique for generating and detecting surface waves on the lung. The motivation was to develop a noninvasive technique for assessing superficial lung tissue disease including interstitial lung disease (ILD). ILD comprises a number of lung disorders in which the lung tissue is stiffened and damaged due to fibrosis of the lung tissue. Currently, chest radiographs and computed tomography (CT) are the most common clinical methods for evaluating lung disease, but they are associated with radiation and cannot measure lung mechanical properties. The novelty of SWE is to develop a noninvasive and nonionizing technique to measure the elastic properties of superficial lung tissue. We propose to generate waves on the lung surface through wave propagation from a local harmonic vibration excitation on the chest through an intercostal space. The resulting surface wave propagation on the lung is detected using an ultrasound probe through the intercostal space. To demonstrate that surface waves can be generated on the lung, an ex vivo muscle-lung model was developed to evaluate lung surface wave generation and detection. In this model, swine muscle was laid atop a swine lung. A vibration excitation of 0.1s 100Hz wave was generated on the muscle surface and the surface waves on the lung were detected using a linear array ultrasound probe at 5MHz. To test its feasibility for patient use, SWE was used to measure both lungs of an ILD patient through eight intercostal spaces. The mean wave speed was 1.71±0.20m/s (±SD) at the functional residual capacity, while the mean wave speed was 2.36±0.33m/s at the total lung capacity. These studies support the feasibility of SWE for noninvasive measurement of elastic properties of lung and demonstrate potential for assessment of ILD.

Velocity measurements of cylindrical surface waves with a large aperture line-focus acoustic transducer

Acoustic microscopy has been widely applied in the measurements of the mechanical properties. However, the measurement of wave velocity on a curved cylindrical surface by acoustic microscopy was seldom reported. In this paper, we adopted a large aperture line-focus PVDF transducer and a defocusing measurement system to measure the velocity of a cylindrical surface waves. The theoretical model was established to study the relationship among the propagation path of surface waves, the geometric parameters of a transducer, and the diameter of a shaft specimen. Based on theoretical deduction and mathematical modeling, theoretical oscillation curves of phase difference were obtained. According to the improved V(f,z) analysis method, the V(f,z) curves were obtained through analyzing experimental data at different frequencies by Fourier transform. Then the surface wave velocity of the cylindrical tungsten steel specimen (Ø 20mm) could be determined by fitting the V(f,z) curves with the theoretical curves. The measurement results were consistent with the theoretical values, indicating that the measurement method was feasible. This study laid the basis for the ultrasonic measurement of the mechanical properties on the layer-coated cylinders.

Laboratory Experiment on the Bed Load Sediment Transport over a Rippled Bed

ABSTRACT Yang, Z.T.; Li, H.J.; Liang, B.C.; Lee, D.Y.; Pan, X.Y., and Xu, Y., 2016. Laboratory experiment on the bed load sediment transport over rippled bed. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 497–501. Coconut Creek (Florida), ISSN 0749-0208. Bed load sediment transport over rippled bedforms was investigated through a series of laboratory experiments with different combinations of bed slope, grain size, wave conditions and water level using a 2D wave flume. In addition to the measurement of surface waves and velocity, the water surface and bottom bed elevation were precisely monitored using video cameras to record the continuous processes of profile evolution, including ripple formation and migration under the assumption of longshore uniformity. The bed load sediment transport flux associated with ripple migration was then estimated....

On the reliability and limitations of the SPAC method with a directional wavefield

The spatial autocorrelation (SPAC) method is one of the most efficient ways to extract phase velocities of surface waves from ambient seismic noise. Most studies apply the method based on the assumption that the wavefield of ambient noise is diffuse. However, the actual distribution of sources is neither diffuse nor stationary. In this study, we examined the reliability and limitations of the SPAC method with a directional wavefield. We calculated the SPAC coefficients and phase velocities from a directional wavefield for a four-layer model and characterized the limitations of the SPAC. We then applied the SPAC method to real data in Karamay, China. Our results show that, 1) the SPAC method can accurately measure surface wave phase velocities from a square array with a directional wavefield down to a wavelength of twice the shortest interstation distance; and 2) phase velocities obtained from real data by the SPAC method are stable and reliable, which demonstrates that this method can be applied to measure phase velocities in a square array with a directional wavefield.

ULTRASOUND VELOCITY VARIATION AT PLASTIC DEFORMATION OF HIGH-CHROMIUM STEEL

The paper is devoted to the research of velocity variation of ultrasound propagation at plastic deformation of corrosion-resistant highchromium steel 40KH13 with ferrite-carbide (as-received condition), martensitic (after hardening) and sorbite (after high-temperature tempering) structures. It has been revealed that each condition demonstrates its own load curve. In as-received condition the load diagram is practically a parabolic one on the whole extent, while in a martensitic condition there is only the stage of a linear deformation hardening, and in a sorbite condition the plastic fl ow curve is three-stage. Using the methods of optic and atomic-force microscopy, the authors have researched the structure of steel at diff erent kinds of thermal treatment. Simultaneously with the regist ration of load curves the researches have conducted the velocity measurement of ultrasound surface waves (Rayleigh waves) in the researched steel at the extension. The realization of the method of velocity variation of Rayleigh waves is in a periodic generation of rectangular impulses with the duration of 100 ns at the input of a radiant piezoelectric transducer and the registration of the passed-by one according to the sample of the wave by means of the receiving piezoelectric transducer, connected up to the digital oscilloscope. The registered signal in a digital form has been used to measure time, passed from the moment of impulse generation at the input of the radiant transducer up to the moment of signal initiation at the output of the receiving transducer. The distance between the transducers during the experiment is constant. It has been shown that the dependence of ultrasound velocity at active loading is defined by the plastic fl ow rule, i.e. the staging of the appropriate loading diagram. The structural condition of the researched steel changes not only the type of the deformation curve at uniaxial tension, but it also changes the dependence character of ultrasound velocity on the deformation.

Field measurements of surface waves using a 5-beam ADCP

This study examines the performance of an improved 5-beam ADCP, with a vertical beam, when deployed to measure non-directional waves in waters of 40m depth. To assess the performance, the ADCP is compared with four co-located directional wave buoys. The surface elevation spectra as measured by the vertical beam compare well with estimates from the buoys in the range 0.10–0.35Hz. Except for peak period, spectral estimates of wave height, mean energy period and spectral bandwidth from the vertical beam agree well with estimates from the buoys, showing only small differences of 2–7%. Some cases exist where either the ADCP or the buoys can resolve particular wave systems that the other sensor cannot resolve, though some of these instances may be the result of numerical artefact. At low frequencies, the ADCP shows a better sensitivity to swell components, and though the buoys can produce low frequency peaks, the difference between the two sensors is particularly evident during low energy sea states. At high frequencies, both sensors may show susceptibility to noise. The study intends to increase the level of confidence in using a 5-beam ADCP with a vertical beam, and of its comparative performance with a different wave sensor.

Spatial Variation of Shear Wave Velocity of Waste Materials from Surface Wave Measurements

The mechanical properties of waste materials are, typically, believed to be more variable than natural soils; however, detailed investigations into the variability of these materials is generally unavailable. The shear wave velocity and its variation with depth and laterally for five different waste types has been measured and analyzed at 26 locations. Shear wave velocity measurements were performed using the multichannel analysis of surface waves (MASW) and microtremor analysis method (MAM) techniques. Statistical analyses were performed for these locations as well as locations available in the literature. Waste types tested include municipal solid waste (MSW) in Subtitle D landfills in Michigan, MSW in a bioreactor landfill, MSW incineration ash, hazardous waste, construction and demolition waste, and municipal water treatment sludge. An empirical shear wave velocity model with depth is calibrated for each of the various waste types. Spatial variability of shear wave velocity is quantified using the coefficient of variation (COV) as a function of depth. The COV of the shear wave velocity of these waste types was found to be similar to values reported in the literature for soil and rock sites.

Multichannel Analysis of Surface Waves and Down-Hole Tests in the Archeological “Palatine Hill” Area (Rome, Italy): Evaluation and Influence of 2D Effects on the Shear Wave Velocity

A joint analysis of down-hole (DH) and multichannel analysis of surface waves (MASW) measurements offers a complete evaluation of shear wave velocity profiles, especially for sites where a strong lateral variability is expected, such as archeological sites. In this complex stratigraphic setting, the high “subsoil anisotropy” (i.e., sharp lithological changes due to the presence of anthropogenic backfill deposits and/or buried man-made structures) implies a different role for DH and MASW tests. This paper discusses some results of a broad experimental program conducted on the Palatine Hill, one of the most ancient areas of the city of Rome (Italy). The experiments were part of a project on seismic microzoning and consisted of 20 MASW and 11 DH tests. The main objective of this study was to examine the difficulties related to the interpretation of the DH and MASW tests and the reliability limits inherent in the application of the noninvasive method in complex stratigraphic settings. As is well known, DH tests provide good determinations of shear wave velocities (Vs) for different lithologies and man-made materials, whereas MASW tests provide average values for the subsoil volume investigated. The data obtained from each method with blind tests were compared and were correlated to site-specific subsurface conditions, including lateral variability. Differences between punctual (DH) and global (MASW) Vs measurements are discussed, quantifying the errors by synthetic comparison and by site response analyses. This study demonstrates that, for archeological sites, VS profiles obtained from the DH and MASW methods differ by more than 15 %. However, the local site effect showed comparable results in terms of natural frequencies, whereas the resolution of the inverted shear wave velocity was influenced by the fundamental mode of propagation.

Comparison of Incoherent and Coherent Wave Field Measurements Using Dual-Polarized Pulse-Doppler X-Band Radar

Radar-based remote sensing for measurement of ocean surface waves presents advantages over conventional point sensors such as wave buoys. As its use becomes more widespread, it is important to understand the sensitivity of the extracted wave parameters to the characteristics of the radar and the scatterers. To examine such issues, experiments were performed offshore of the Scripps Institution of Oceanography pier in July 2010. Radar measurements in low wind speeds were performed with a dual-polarized high-resolution X-band pulse-Doppler radar at low grazing angles along with two independent measurements of the surface waves using conventional sensors, a GPS-based buoy, and an ultrasonic array. Comparison between radar cross section (RCS) and Doppler modulations shows peak values occurring nearly in-phase, in contrast with tilt modulation theory. Spectral comparisons between Doppler-based and RCS-based spectra show that Doppler-based spectra demonstrate greater sensitivity to swell-induced modulations, whereas RCS-based spectra show greater sensitivity to small-scale modulations (or generally have more noise at high frequency), and they equally capture energy at the wind wave peak. Doppler estimates of peak period were consistent with the conventional sensors, whereas the RCS differed in assignment of peak period to wind seas rather than swell in a couple of cases. Higher order period statistics of both RCS and Doppler were consistent with the conventional sensors. Radar-based significant wave heights are lower than buoy-based values and contain nontrivial variability of ∼33%. Comparisons between HH and VV polarization data show that VV data more accurately represent the wave field, particularly as the wind speeds decrease.

Automated Surface Wave Measurements for Evaluating the Depth of Surface-Breaking Cracks in Concrete

The primary objective of this study is to investigate the feasibility of an innovative surface-mount sensor, made of a piezoelectric disc (PZT sensor), as a consistent source for surface wave velocity and transmission measurements in concrete structures. To this end, one concrete slab with lateral dimensions of 1500 by 1500 mm and a thickness of 200 mm was prepared in the laboratory. The concrete slab had a notch-type, surface-breaking crack at its center, with depths increasing from 0 to 100 mm at stepwise intervals of 10 mm. A PZT sensor was attached to the concrete surface and used to generate incident surface waves for surface wave measurements. Two accelerometers were used to measure the surface waves. Signals generated by the PZT sensors show a broad bandwidth with a center frequency around 40 kHz, and very good signal consistency in the frequency range from 0 to 100 kHz. Furthermore, repeatability of the surface wave velocity and transmission measurements is significantly improved compared to that obtained using manual impact sources. In addition, the PZT sensors are demonstrated to be effective for monitoring an actual surface-breaking crack in a concrete beam specimen subjected to various external loadings (compressive and flexural loading with stepwise increases). The findings in this study demonstrate that the surface mount sensor has great potential as a consistent source for surface wave velocity and transmission measurements for automated health monitoring of concrete structures.

The acquisition and measurement of surface waves of high-speed liquid jets.

The instability analysis of the liquid jet issuing into ambient air was conducted with an emphasis placed upon the evolution of surface waves of the jet. An experiment was designed to visualize the microscopic morphology on the surface of a liquid jet. A spectral method was proposed to measure wavelength from the obtained jet images. We also discuss key setup parameters that significantly affect the resolution of desired jet features and the accuracy of the spectral measurement. The results show that the liquid jet near the nozzle exit can be divided into a laminar section, a transition section, an instability section, and a turbulence section. Surface wave scales range from 0.06 to 0.11 times of the nozzle diameter with the atomization breakup regime. For the atomization breakup regime, the growth ratio of the surface waves of the instability section is 0.06 which is 1.5 times the value of the second wind-introduced breakup regime and 3 times the value of the first wind-introduced breakup regime.Graphical abstract