Shadow Zone Research Articles

The State of the Stratosphere Throughout the Seasons: How Well Can Atmospheric Models Explain Infrasound Observations at Regional Distances?

The stratosphere is the atmospheric layer with the strongest impact on long-range infrasound propagation. Natural and anthropogenic infrasound signals are efficiently ducted between refraction altitudes of 30 to 60 km and reflections on the ground and are thus propagated to infrasound receivers over long distances. The direction of favorable stratospheric ducting depends on the state of the atmosphere, primarily driven by the seasonal variation of stratospheric winds. This study uses a dataset of ground-truth infrasound events over two decades and all seasons to assess the station detectability and atmospheric model performance to correctly estimate according station observations and propagation conditions. From 2000 to 2019, the German Aerospace Center facility in Lampoldshausen has conducted ignition tests of the Ariane 5 main rocket engine. Out of the 159 engine tests considered in this study, 71 were observed at the infrasound array IS26 in the Bavarian forest, located eastward at 320 km distance. Observations were mostly made during wintertime, whereas reversed stratospheric wind patterns during summertime inhibited signal detections. A significant portion of wintertime non-detections however corresponded to stratospheric profiles that should enable signal observations. Using European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric model analyses and infrasound ray tracing only two-thirds of the non-detections could be explained by the existence of a near-station acoustic shadow zone. It must thus be concluded that the applied atmospheric model is more often than expected unable to correctly explain infrasound propagation and observation at regional distances.

Inversion of Sound Speed and Thickness of High-Speed Sediment Using Interference Structure in Shadow Zone

The geoacoustic parameter acquisition in the deep sea is of great significance to the research of ocean acoustics. This paper found that the interference structure of the shadow zone induced by the reflection of the high-speed sediment layer could be simply described by the grazing angle of the surface-bottom reflection from the theory of ray acoustics, when the source and receiver depth makes the grazing angle of the surface-bottom reflection consistent with that of the bottom-surface reflection. On this basis, a geoacoustic parameter inversion method by spatial position matching of interference fringes in the shadow zone was proposed, and an interference fringe extraction method was designed based on the maximum between-class variance algorithm in this paper. After extracting the results by the stripe coordinates in the simulation environment, the density was obtained by assuming the base sound speed as an empirical value and combining with Hamilton’s empirical formula, and the sediment sound speed and thickness were inverted by the grid search method. Those inversion results were compared with the multi-dimensional inversion results of the genetic algorithm. The simulation results showed that the fringe extraction method proposed in this paper could effectively extract the interference fringes formed by the reflection of the high-speed sediment in the shadow zone, and compared with the multi-dimensional optimization process, the relatively accurate inversion results of the sound speed and thickness of high-speed sediment could be obtained more effectively and quickly by taking the spatial position of the interference fringe as the cost function of the matching parameter combined with the grid search method in this paper.

Complex eigenrays algorithm for infrasound propagation in a windy range dependent atmosphere.

Ray tracing is a simple and efficient three-dimensional method which reduces the problem of infrasound propagation to a series of one-dimensional cases along acoustical rays. However, in relatively frequent cases, infrasound stations are located in geometrical shadow zones, where only diffracted waves are recorded. The corresponding arrivals cannot be predicted by ray theory. To simulate infrasound propagation in these zones, the ray tracing method is generalized to complex ray theory. The source, media, and ground parameters are all considered as complex numbers. For applications with realistic atmospheric data, including stratified temperature and wind as well as the range dependency of atmospheric profiles, an efficient algorithm determining complex eigenrays in the shadow zones is presented. It is illustrated by a two-dimensional case of a point source.

Impact of topography on attenuation of noise from a cement plant in a hilly terrain

The influence of hill topography on noise from industrial plants is scantly documented, despite the fact that the noise profiles can vary in plains and in hilly terrain. Significant noise data from a cement plant flanked by hills were collected and analyzed for its attenuation over space in the direction of the valley and across the hills. It was observed that the noise attenuation is not similar to that experienced in plains owing to interactions with the mountains. The overall effect has been modelled over different distances between the four sources of the noise and several monitoring stations. The analyzed noise data showed that the influence of the major source of noise is obvious, yet difficult to differentiate. An iterated weighted distance from the noise sources, proved to be a better estimate for distance while modelling the attenuation of the noise. A relationship between the equivalent noise levels during the day and night could also be established. The effect of relative altitude and slope could be modelled using nonlinear multivariate analysis and the response surfaces were obtained for minimum, maximum and average values of the variables. Noise shadow zones could be identified with noise contouring which reflects reduction in the noise levels on hind side of the hills. The impact of topography and possible interference could thus be defined in such hilly terrain. The information can be used to define the noise mitigation strategies for adjacent habitats and mitigation of human response. The findings of the paper can also be used by prospective plants in hilly areas.

Proper location of the transducers for an active noise barrier

The main intention of this study is to propose general criteria for the locations of the control sources and error microphones that improve the performance of the active noise barrier. Based on the proposed criteria of this study, the greater reduction is attained when the diffracted field of the noise source is canceled with the diffracted field of the control sources, that is, it is suggested to locate the control sources on the incident side and below the path that connects the furthest point in the shadow zone to the edge of the barrier. Furthermore, it is suggested that the error microphones are most suitably placed on the shadow side of the barrier where they are under the diffracted field of both the primary and control sources. The results also show that with these general criteria, the active noise control achieves an extra reduction that varies from 14.9 to 3.9 dB (for the one-third octave bands from 63 Hz to 1 kHz) and 9.3 dB for the broadband noises.

Two dimensional dynamically focused beam migration in weakly anisotropic media

Anisotropy exists widely in the earth medium. For anisotropic medium, the traditional isotropic migration will lead to the inaccurate images and unfocused energy. Especially for a deep target exploration, ignoring anisotropy will further affect the subsequent seismic data interpretation. As an improved ray method, Gaussian beam migration overcomes the imaging problems of caustics and shadow zones in Kirchhoff migration, and avoids the time-consuming problems of wave equation migrations. However, the imaging quality of the Gaussian beam migration is controlled by the initial beam width at the surface. In this paper, we extend Nowack (2011)’s algorithm to anisotropic media and present an anisotropic dynamically focused beam migration by modifying the propagator of the Gaussian beams. We use anisotropic kinematic and dynamic ray tracing with optimized coefficients to obtain travel times, trajectories and dynamic information. We then use dynamically focused beams for weakly anisotropic media to calculate the Green's function and the Claerbout imaging condition to obtain images. This strategy enables us to improve the imaging quality in the middle and deep layers without reducing the imaging quality in the shallow layers, which will help to overcome the limitation of the initial beam width in Gaussian beam migration. The results for a VTI fault model and the Shengli complex structure model show the accuracy and validity of the proposed method in this paper.

Infrasound propagation through the atmosphere with mesoscale wind velocity and temperature fluctuations

Some results on modeling and observation of infrasound propagation in the atmosphere in a presence of mesoscale and anisotropic wind velocity and temperature fluctuations are presented. The theoretical model of infrasound scattering from anisotropic wind velocity and temperature inhomogeneities of the atmosphere is developed. With this model, the appearance of the stratospheric, mesospheric, and thermospheric arrivals of the infrasound signals in the acoustic shadow zones is explained. The analytic relation between the wave field of the scattered infrasound signal and the vertical profile of the effective sound speed fluctuations is obtained. Using this relation, the vertical profiles of the fluctuations within the upper stratosphere (25–55 km) and the lower thermosphere (105–140 km) were retrieved from the waveforms and travel times of the signals recorded in the acoustic shadow zones. The theoretical frequency spectrum of the infrasound wavefield reflected from the fine-scale layered structure of the atmosphere is obtained and compared with the spectra of the observed stratospheric arrivals.

The Far Side of Mars: Two Distant Marsquakes Detected by InSight

Abstract For over three Earth years the Marsquake Service has been analyzing the data sent back from the Seismic Experiment for Interior Structure—the seismometer placed on the surface of Mars by NASA’s InSight lander. Although by October 2021, the Mars seismic catalog included 951 events, until recently all these events have been assessed as lying within a radius of 100° of InSight. Here we report two distant events that occurred within days of each other, located on the far side of Mars, giving us our first glimpse into Mars’ core shadow zone. The first event, recorded on 25 August 2021 (InSight sol 976), shows clear polarized arrivals that we interpret to be PP and SS phases at low frequencies and locates to Valles Marineris, 146° ± 7° from InSight. The second event, occurring on 18 September 2021 (sol 1000), has significantly more broadband energy with emergent PP and SS arrivals, and a weak phase arriving before PP that we interpret as Pdiff. Considering uncertain pick times and poorly constrained travel times for Pdiff, we estimate this event is at a distance between 107° and 147° from InSight. With magnitudes of MwMa 4.2 and 4.1, respectively, these are the largest seismic events recorded so far on Mars.

Nikolai Myaskovsky – 140th birth anniversary. Rediscovering the composer in the present times

Abstract On the occasion of the 140th anniversary of composer Nikolai Myaskovsky’s birth, in the spring of 2021, in the city of Ekaterinburg there took place the Myaskovsky Dialogues festival dedicated entirely to the Russian composer, being one of the few musical events with a musical programme based on his works. Known as the “father” of the Soviet symphony, Nikolai Myaskovsky was one of the pillars of resistance in Russian music culture in the first half of the 20th century, managing to maintain a stylistic balance between traditional genres, harmonic language with innovative tendencies, ideas promoted within the new political system and a neutral way of integrating communist ideals musically. Although his contemporaries perceived him with respect and consideration, N. Myaskovsky was discredited after the tensions and political events of 1948, entering a shadow zone during the Cold War, until the fall of the Iron Curtain. Therefore, it was only in the last three decades that he was rediscovered in the music world, due to the interest given to his works by well-known conductors such as E. Svetlanov, V. Gergiev, V. Petrenko, V. Jurowski. In this paper, our aim is to accomplish a historical perspective on N. Myaskovsky’s rediscovery and his approach in concert programs, records, reviews, chronicles, articles, musicological studies, papers and volumes from the 1970s to the present.

Effects of mesoscale eddies on the spatial coherence of a middle range sound field in deep water

Mesoscale eddies have a remarkable influence on the underwater sound field. Many previous studies have investigated the effects of eddies on transmission loss, the convergence zone, time delay, etc. However, the effects of eddies on spatial coherence are less well studied and remain unclear. In this paper, the effects of eddies on spatial coherence at the subsurface in deep water are investigated. The eddy environments are simulated with Gaussian eddy equations, the complex pressure field is obtained using a range-dependent parabolic equation model and the associated mechanism is analyzed based on ray theory and models. The results show that cold/warm mesoscale eddies affect spatial coherence in a high-intensity zone by changing the locations and width of the convergence zone. In the shadow zone, the horizontal correlation radius and the vertical correlation radius increase with range and decrease with depth, and they are increased by warm eddies and decreased by cold eddies, mainly caused by variation of the multipath structure.

Investigation of traffic noise attenuation potential of an urban highway underpass

Road traffic is the main contributor to noise in urban areas. A case of concern is urban highways, due to the intensity of the emitted noise. Acoustic barriers are one of the solutions usually adopted to reduce highway traffic noise in this case. However, they have a negative visual impact on the urban landscape. An underpass could be a solution that provides noise attenuation without introducing aesthetical problems to the urban area. This work investigates the noise attenuation of a highway underpass aiming to confirm its efficiency as a solution for the minimization of traffic noise and explores a variety of scenarios that could influence the noise propagation. Noise measurements and the collection of input data used in noise simulations were conducted at an urban highway located in the city of João Pessoa in Brazil. The investigation was focused on the highway underpass with an L-shaped top edge, which is acting as a parallel acoustic barrier to an adjacent residential area. In addition, simulations were performed using the software SoundPLAN. Five scenarios were simulated: the actual situation and four scenarios with different depths of the underpass and changes on its edge. It was found that the existing L-shape edge of the underpass is positively influential only at points at the immediate vicinity of the border and resulted in an additional average attenuation of 1.3 dB in this region. However, in general, the average attenuation due to the underpass for the points in the whole acoustic shadow zone was 10.6 dB with the actual L-shape edge, and 13.1 dB from simulations when the L-shaped edge was removed. From simulations involving changing the depth of the underpass, it was observed that there was no linear relationship between attenuation versus depth. The simulation results showed that adding an L-shape edge with its current length is not efficient regardless of the depth of the underpass. The results thus confirmed the underpass as an effective solution for the mitigation of highway traffic noise and provided additional insight on the role of the depth associated to changes on the geometry of the top of the underpass.

Shadow zone in MQL application and its influence on lubricant deficiency and machinability during micro-milling

Minimum quantity lubrication (MQL) in metal cutting helps enhancing machinability while ensuring sustainability. In the absence of bulk heating in micro-milling, the cutting fluid needs to be deposited on the tribologically active chip-tool-workpiece region to perceive enhanced lubrication effect. There are few factors that can restrict the oil droplets from depositing on the tool. One such restriction that inherently appears as “Shadow Zone” during end-milling process is reported in this article for the first time. This shadow zone hinders certain percentage of droplets from reaching to the cutting edges resulting in reduced wetting capability of the MQL supply even when the overall oil flow rate remains unchanged. Lubricant deficiency induced solely by this shadow zone during micro-milling under varying parameters is assessed here. For fixed nozzle orientation, detrimental effect of the shadow zone intensifies with an increase in the axial depth of cut and top-burr height. At 50 µm axial depth, the shadow zone restricts 3.7% droplets from depositing on the active cutting edge and thereby compels the MQL assisted cutting process to rotate in incompletely lubrication condition. For unchanged oil flow rate, the corresponding deficiency increases to 16.4% at 200 µm axial depth. When compared with dry micro-milling of Ti-6Al-4 V, shadow zone reduces effectiveness of the MQL supply in controlling tool wear from 25.4 – 5.5% in the entire tool life when axial depth is increased from 50 – 200 µm. Similar degree of reduction in MQL effectiveness towards controlling surface roughness, burr width, and cutting forces is also observed.

Horizontal refraction and diffraction of underwater sound around an island.

The three-dimensional (3D) propagation effects of horizontal refraction and diffraction were measured on a tetrahedral hydrophone array deployed near the coast of Block Island, RI. Linear frequency modulated chirp signals, centered at 1 kHz with a 400 Hz bandwidth, were transmitted from a ship moving out of the acoustic shadow zone blocked by the island from the perspective of the hydrophone array. The observed shadow zone boundary was consistent with the prediction made by a 3D sound propagation model incorporating high-resolution bathymetry and realistic sound speed obtained from a data-assimilated regional ocean model. The 3D modal ray calculation provided additional insight into the frequency dependence of the signal spreading. This analysis found that the modes at higher frequencies can propagate closer to the coast of the island with shallower modal cutoff depths, where the sound energy penetrates the sloping seafloor at supercritical incidence. The evidence of horizontal caustics of the sound was shown in the parabolic equation and modal ray models by comparing to the arrival pattern observed in the data. The arrival angle measurements on the tetrahedral array show the complex propagation patterns, including the diffracted energy in the island shadow and acoustic energy refracted away from the island.

Blue-shifted deep ocean currents in the equatorial Indian Ocean

Spectra from two decades of zonal current data at $$\sim $$ 4000 m in the central and western equatorial Indian Ocean show a shift in the dominant frequencies from the west to the east. The 120–180-day period is stronger at 77 $$^\circ $$ E, the 60–120-day period at 83 $$^\circ $$ E, and the 30–90-day period at 93 $$^\circ $$ E. The weakening of lower frequencies near the eastern boundary can be explained using theoretical ray paths of Kelvin waves and reflected Rossby waves. The equatorial Kelvin wave forced by winds reflects from the eastern boundary as Rossby waves with different meridional modes. After reflection, the low (high) frequency Rossby beams travel a larger (shorter) distance before reaching the bottom, thereby creating a shadow zone, a region with low wave energy, between the ray path and the eastern boundary. The shift in frequency with longitude is not evident in the top 1000 m, where the current is dominated by the semi-annual cycle.

Ways to improve state support for small business in the development of foreign economic activity of the Russian Federation

The purpose of the review and comparison in this paper is a comparative analysis of measures to overcome the consequences of the pandemic for the systematic improvement of the regulation of the activities of Russian small businesses in support of their entry into foreign markets. Small business is the sphere of employment of citizens of our country, and its decline threatens serious social problems that can lead to increased imbalances in spatial development and the emergence of new depressed regions. In conditions when small businesses largely remain in the shadow zone, the possibility of receiving popular forms of support from the state in times of crisis can become an incentive for restarting and modernizing production. Currently, small businesses have not realized their potential as a commodity producer, a supplier of funds to the budget and a school for raising the middle class of well-off citizens. The paper considers and analyzes the norms of measures in force in the Russian Federation to support small and medium-sized businesses. A retrospective analysis of the current regulatory framework is carried out. In addition, the aspect of the application of promising directions in the development of scientific and technological progress and the relevance of its results in the general theory of business management is studied. The authors propose adjustments and additions to the management model of small and medium-sized businesses, taking into account the increasing opportunities of scientific and technological progress, development and improvement of the general theory of management and the prospects of working in foreign markets. Theoretical and/or practical significance. The conducted research helps to supplement the theoretical picture of the effectiveness of the application of the regulatory framework by small and medium-sized businesses and ensures the steady progressive development of the theory of entrepreneurship management in the current epidemiological situation in the country.

Three Dimensional Volume Coverage in Multistatic Sonar Sensor Networks

Recent changes in the design of enemy threats such as submarines and the technological achievements in sensor development have paved the way for multistatic sonar applications, which increase security and situational awareness in underwater tactical operations. Previously, coverage in multistatic sonar sensor networks (MSSN) was studied using Cassini ovals and the traditional sonar detection model in two dimensions without any discussion of the practicability and feasibility in terms of conditions related to the underwater acoustic propagation environment. In this study, a practical three-dimensional MSSN channel model is proposed. The proposed model covers a spectral variation of absorption loss, ambient noise, sound speed profile, and shadow zones. The realistic effects of sound propagation and environmental conditions are modeled and evaluated using Lybin, which is a well-known sonar performance prediction tool. Using the practical MSSN channel model, the number of source-receiver pairs required to cover a three-dimensional MSSN volume is calculated. The impacts of frequency, source-to-receiver distance, and source level are investigated. The results are compared to the Cassini oval and traditional sonar detection models via an error expression derived according to our verified practical model. The results reveal that the inclusion of ambient conditions and sound propagation characteristics in the channel model leads to huge error levels of 4700000% in the Cassini oval model and 170000% in the traditional sonar detection model, depending on frequency. Thus, the applicability of these models in realistic MSSN deployment scenarios is limited.

Accounting for insolation in solving thermophysical problems

The article considered the problem of the influence of insolation on the depth of soil freezing. In sunny and shadow zones, the building has different freezing and thawing conditions. Natural and laboratory excrement were carried out to determine the difference in soil temperatures. Based on the data obtained experimentally, a numerical calculation of the building-base model was made.

Ways to reduce entrepreneurial risks on the example of small business development in the Moscow Region

The purpose of consideration and comparison in this work is a comparative analysis of measures of state support for small and medium-sized businesses in the Moscow Region. Some types of entrepreneurship are a sphere of mass employment of the population, and a recession in them may cause serious social problems that can lead to an increase in imbalances in spatial development and the emergence of new depressed territories (a number of industries are characterized by a high concentration in certain cities or regions). In conditions when small business largely remains in the shadow zone, the opportunity of receiving much-needed forms of support from the state in times of crisis can become an incentive for restarting and modernizing production. The authors have proposed adjustments and additions to the small and medium-sized business management model, taking into account the increasing possibilities of scientific and technological progress, the development and improvement of the general management theory. The study helps to complement the theoretical picture of the relationship between the business environment and government bodies that control the economic activities of the participants, as well as provides a sustainable progressive development of the theory of business management in the current epidemiological situation in the country.

Generation Mechanisms of Mesoscale Eddies in the Mauritanian Upwelling Region

AbstractThe physical processes driving the genesis of surface- and subsurface-intensified cyclonic and anticyclonic eddies originating from the coastal current system of the Mauritanian upwelling region are investigated using a high-resolution (∼1.5 km) configuration of GFDL’s Modular Ocean Model. Estimating an energy budget for the boundary current reveals a baroclinically unstable state during its intensification phase in boreal summer and which is driving eddy generation within the near-coastal region. The mean poleward coastal flow’s interaction with the sloping topography induces enhanced anticyclonic vorticity, with potential vorticity close to zero generated in the bottom boundary layer. Flow separation at sharp topographic bends intensifies the anticyclonic vorticity, and submesoscale structures of low PV coalesce to form anticyclonic vortices. A combination of offshore Ekman transport and horizontal advection determined the amount of South Atlantic Central Water (SACW) in an anticyclonic eddy. A vortex with a relatively dense and low PV core will form an anticyclonic mode water eddy, which will subduct along isopycnals while propagating offshore and hence be shielded from surface buoyancy forcing. Less contribution of dense SACW promotes the generation of surface anticyclonic eddies as the core is composed of a lighter water mass, which causes the eddy to stay closer to the surface and hence be exposed to surface buoyancy forcing. Simulated cyclonic eddies are formed between the rotational flow of an offshore anticyclonic vortex and a poleward flowing boundary current, with eddy potential energy being the dominant source of eddy kinetic energy. All three types of eddies play a key role in the exchange between the Mauritanian coastal currents system and the adjacent eastern boundary shadow zone region.

Экспериментальная оценка формирования взрывоопасной среды над плавающей крышей резервуара для хранения нефти в процессе откачки при пожаре соседнего резервуара

Introduction. The study of the formation of explosive concentrations of vapors of flammable liquids (hereinafter referred to as flammable liquids – LVL) in the gas space of a tank with a floating roof when pumping oil out of it during a fire of a neighboring tank in oil storage facilities in Vietnam. Goal and tasks. Consider the reasons for the spread of fire from a burning vertical, steel floating-roof oil storage tank (hereinafter – RVSPK) to an adjacent non-burning RVSPK with oil. Develop a program of experiments. Create an industrial experimental setup for measuring explosive and fire hazardous concentrations of light oil fractions above the floating roof of a full-scale reservoir with a volume of 65 000 m3 of crude oil. Conduct an experiment to measure the concentration of light fractions of oil over a floating roof during pumping. To experimentally determine the possibility of the formation of explosive and fire hazardous concentrations of light fractions of oil (methane), within the lower concentration limit of flame propagation, in the steam space above the floating roof of the RVSPK in real time in the process of lowering the level of the floating roof during pumping out oil in the event of a fire on a neighboring tank. Method. Analysis. Full-scale experiment. Results and discussion. A natural experiment was carried out. The results of studies on the distribution of concentrations of combustible vapors of light fractions of oil (methane) in the gas space above the floating roof of a non-combustible tank of 65000 m3 during oil pumping are obtained. The most probable places of formation of explosive concentrations are determined. To reduce the fire load, the risk of fire spread, possible damage and death caused by fire in large-capacity RVSPK oil storage facilities in Vietnam, it is proposed to pump oil from the adjacent RVSPK to the burning RVSPK in combination with concentration control in the aerodynamic shadow zone inside the RVSPK gas space. Conclusions. When crude oil is pumped out of the tank in the annular zone around the floating roof, an explosive methane-air mixture zone is formed with a methane concentration reaching the lower concentration limit of flame propagation. Keywords: fire, fire and explosion safety, reservoir, floating roof, concentration, combustion.