Figure 9 - uploaded by Daniel C. Bowman
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A ray diagram showing acoustic propagation paths in the stratospheric duct and the position of the free flying sensors for Shot 1 and Shot 2. The vertical domain of the ECMWF model is about 80 km, and the domain of the GFS model is about 47 km.
Source publication
A variety of Earth surface and atmospheric sources generate low frequency sound waves that can travel great distances. Despite a rich history of ground-based sensor studies, very few experiments have investigated the prospects of free floating microphone arrays at high altitudes. However, recent initiatives have shown that such networks have very l...
Contexts in source publication
Context 1
... ray launch azimuth was 300 • from north, Balloon-borne Infrasound Network 11 passing close to the center of the balloon cluster for both explosions. The propagation pattern indicates that the sensors were in the acoustic shadow for both explosions (Figure 9), regardless of which atmospheric model was used. This explains the lack of detection for Shot 1 but not the high amplitude arrivals observed from Shot 2. ...
Context 2
... is sufficient to capture Shot 2. Evidently signals from Shot 2 were intercepted after refracting from the upper stratosphere but before bouncing off of the ground surface ( Figure 9). Acoustic velocity perturbations should have the greatest effect when the ray path is nearly horizontal, which takes place at altitudes between 35 and 45 km in this experiment. ...
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In the frame of the European H2020 project ARISE, a short wave infrared (SWIR) InGaAs camera has been operated at the Haute-Provence Observatory, during a night that corresponds to the peak of Geminid meteor shower to investigate infrasound associated with meteor arrivals. This camera allows continuous observations during clear-sky nighttime of the...
Citations
... Numerous authors have reported balloon pressure detections of direct infrasound waves from surface explosions or seismic hammers [12,61,68]. However, due to the lack of dedicated seismo-acoustic experiments and the complexity of atmospheric path effects, both seismically generated epicentral infrasound and Rayleigh wave infrasound detections are still lacking, making the systematical validation of modeling and inversion methods challenging. ...
The analysis of infrasound waves has a significant potential for retrieving a range of geophysical parameters across various scales, such as atmospheric structures, characteristics of surface and buried sources, and seismic velocity structures. This potential was recently showcased in infrasound studies that illustrated the ability to retrieve Earth’s shallow velocities and Mars’ near-surface atmospheric winds from remote acoustic observations. Consequently, infrasound is becoming an essential component of planetary missions, providing insights into the interiors and atmospheres of other terrestrial planets in the solar system. However, utilizing infrasound data requires efficient forward wave simulation techniques and an accurate description of waveform sensitivity to source and medium parameters. Even under ideal conditions, many inverse problems associated with infrasound-based probing are inherently ill-posed, necessitating regularization or other approaches to ensure reliable results. In this contribution, we highlight recent seismo-acoustic research findings, addressing atmospheric probing at both smaller and global scales, as well as innovative methods to accelerate infrasonic wave propagation modeling.
... The first well-documented full-day heliotrope flight occurred in 2016, which like the current BASS campaign carried a microbarometer to measure infrasound (i.e., sound at frequencies below human hearing, <20 Hz) (Young et al. 2018). The quasi-spherical shaped balloon envelope was first termed heliotrope during a separate flight campaign in 2017 (Bowman and Albert 2018). Most scientific uses of the heliotrope have been focused on recording acoustic waves and in situ measurements of stratospheric aerosols. ...
Heliotropes are passive solar hot air balloons that are capable of achieving nearly level flight within the lower stratosphere for several hours. These inexpensive flight platforms enable stratospheric sensing with high-cadence enabled by the low cost to manufacture, but their performance has not yet been assessed systematically. During July to September of 2021, 29 heliotropes were successfully launched from Oklahoma and achieved float altitude as part of the Balloon-based Acoustic Seismology Study (BASS). All of the heliotrope envelopes were nearly identical with only minor variations to the flight line throughout the campaign. Flight data collected during this campaign comprise a large sample to characterize the typical heliotrope flight behavior during launch, ascent, float, and descent. Each flight stage is characterized, dependence on various parameters is quantified, and a discussion of nominal and anomalous flights is provided.
... The first well-documented full-day heliotrope flight occurred in 2016, which like the current BASS campaign carried a microbarometer to measure infrasound (i.e., sound at frequencies below human hearing, < 20 Hz) (Young et al. 2018). The quasi-spherical shaped balloon envelope was first termed heliotrope during a separate flight campaign in 2017 (Bowman and Albert 2018). Most scientific uses of the heliotrope have been focused on recording acoustic waves and in situ measurements of stratospheric aerosols. ...
Heliotropes are passive solar hot air balloons that are capable of achieving nearly level flight within the lower stratosphere for several hours. These inexpensive flight platforms enable stratospheric sensing with high-cadence enabled by the low cost to manufacture, but their performance has not yet been assessed systematically. During July to September of 2021, 29 heliotropes were successfully launched from Oklahoma and achieved float altitude as part of the Balloon-based Acoustic Seismology Study (BASS). All of the heliotrope envelopes were nearly identical with only minor variations to the flight line throughout the campaign. Flight data collected during this campaign comprise a large sample to characterize the typical heliotrope flight behavior during launch, ascent, float, and descent. Each flight stage is characterized, dependence on various parameters is quantified, and a discussion of nominal and anomalous flights is provided.
... The primary noise concern for an ascending balloon, however, is additional wind noise due to the payload box traveling in the balloon's wake (Barat et al., 1984). Research has shown that wind noise dominates during a balloon's ascent (Krishnamoorthy et al., 2020), thus previous efforts to collect explosion signals have focused on free-floating balloons during periods of neutral buoyancy (Bowman & Albert, 2018;Young et al., 2018). Studies of stratospheric noise, however, have shown that wind noise during ascent through the stratosphere is drastically reduced compared to the troposphere (Bowman & Lees, 2015). ...
Plain Language Summary
A surface chemical explosion was observed by pressure and acceleration sensors suspended from an ascending free‐floating balloon at a height of 35 km and a total propagation distance of 127 km from the blast. The balloon's sensor package included a smartphone collecting different types of data (including audio, acceleration, and position), as well as more traditional infrasound and location sensors. The explosion signal was observed by the airborne pressure and vertical accelerometer sensors, as well as by surface‐deployed traditional and smartphone pressure and acceleration sensors. The blast signatures recorded by the airborne and ground‐based stations are compared to provide insight into the present capabilities, limitations, and possible improvements to future balloon‐borne collections of seismo‐acoustic signatures on Earth and beyond.
... A constant recording of the microbarom is unusual at the ground surface because of wind noise, suggesting that sensors at altitude are more sensitive than those at the ground surface due to the environment in which they operate in. These experiments led to the Heliotrope experiment where Bowman and Albert (2018) launched a network of five heliotrope solar balloons to create a sparse array in the sky. This array maintained an approximately 50-100 km horizontal aperture for several hours and at altitudes from ∼21 to 24 km above sea level. ...
The Sound Fixing and Ranging (SOFAR) channel in the ocean allows for low frequency sound
to travel thousands of kilometers, making it particularly useful for detecting underwater nuclear explosions.
Suggestions that an elevated SOFAR-like channel should exist in the stratosphere date back over half a century
and imply that sources within this region can be reliably sensed at vast distances. However, this theory has
not been supported with evidence of direct observations from sound within this channel. Here we show
that an infrasound sensor on a solar hot air balloon recorded the first infrasound detection of a ground truth
airborne source while within this acoustic channel, which we refer to as the AtmoSOFAR channel. Our results
support the existence of the AtmoSOFAR channel, demonstrate that acoustic signals can be recorded within
it, and provide insight into the characteristics of recorded signals. Results also show a lack of detections
on ground-based stations, highlighting the advantages of using balloon-borne infrasound sensors to detect
impulsive sources at altitude.
... For high-altitude infrasound sensing, no studies to date have directly explored the effect of gravity wave perturbations to the wind field on acoustic wave propagation and signal arrival times. The likely presence of small-scale structures caused by gravity waves has been noted in relation to high-altitude balloon infrasound sensing at regional distances [20,43,44]. In their investigation of event localization by a balloon-borne infrasound sensor network, Bowman and Albert [44] noted that some signals were detected despite the receiver being within a predicted shadow zone. ...
... The likely presence of small-scale structures caused by gravity waves has been noted in relation to high-altitude balloon infrasound sensing at regional distances [20,43,44]. In their investigation of event localization by a balloon-borne infrasound sensor network, Bowman and Albert [44] noted that some signals were detected despite the receiver being within a predicted shadow zone. They postulated that this was direct evidence of wind perturbations in the lower stratosphere but did not pursue this line of inquiry any further. ...
... Geometric ray tracing is well-suited for frequencies typically observed by high-altitude sensors, as well as high elevation sources and steep angle arrivals, and therefore it has been extensively used to describe balloon-borne infrasound propagation (e.g., [20,40,[42][43][44]). In fact, previous studies involving balloon-borne infrasound have shown that geometric ray tracing accurately describes direct airwave arrivals and travel times for direct arrivals (e.g., [40]). ...
High-altitude balloons carrying infrasound sensor payloads can be leveraged toward monitoring efforts to provide some advantages over other sensing modalities. On 10 July 2020, three sets of controlled surface explosions generated infrasound waves detected by a high-altitude floating sensor. One of the signal arrivals, detected when the balloon was in the acoustic shadow zone, could not be predicted via propagation modeling using a model atmosphere. Considering that the balloon’s horizontal motion showed direct evidence of gravity waves, we examined their role in infrasound propagation. Implementation of gravity wave perturbations to the wind field explained the signal detection and aided in correctly predicting infrasound travel times. Our results show that the impact of gravity waves is negligible below 20 km altitude; however, their effect is important above that height. The results presented here demonstrate the utility of balloon-borne acoustic sensing toward constraining the source region of variability, as well as the relevance of complexities surrounding infrasound wave propagation at short ranges for elevated sensing platforms.
... However, PMWE moving with high horizontal speed were not registered at these occasions. Moreover, infrasound measurement instrumentation is mainly ground-based, with a limited number of balloon-borne observations (e.g., Bowman and Albert, 2018). Also, it is difficult to measure electron density gradients directly and with a high vertical resolution of a few hundred meters in the lower ionosphere, i.e. at the PMWE altitudes. ...
We considered three events on 4 November 2015, 22 December 2016, and 12 November 2018, when the signals travelling in the polar winter mesosphere with high horizontal velocities above 300 m/s were measured by the atmospheric radar ESRAD (Chilson et al., 1999) located at Esrange, near Kiruna in northern Sweden. We proposed four mechanisms of generation of such special cases of polar mesosphere echoes, e.g. high-speed PMWE, that involve microbaroms, i.e. infrasound waves at 0.1-0.35 Hz frequencies created by ocean swell. These mechanisms are (i) generation of viscous waves, (ii) generation of thermal waves, (iii) direct contributions of infrasound, and (iv) generation of secondary waves at sound dissipation. These processes necessarily accompany sound propagation in inhomogeneous, thermally conducting and viscous fluid (air). The four models were theoretically analysed and their efficiency was estimated. The infrasound measurements at the IS37 station (Gibbons et al., 2019) located about 170 km north-west from the ESRAD radar, modelled maps of the microbarom sources, infrasound propagation conditions and ionospheric conditions for these three PMWE events support the proposed models. Infrasound-generated thermal waves are suggested to be the most probable specific cause of the observed high-speed, high-aspect-ratio PMWE events. However, absence of in-situ infrasound and plasma measurements did not allow us to quantify contributions of individual physical mechanisms to the fast-travelling echoes generation.
... However, PMWE moving with high horizontal speed were not registered at these occasions. Moreover, infrasound measurement instrumentation is mainly ground-based, with a limited number of balloon-borne observations (e.g., Bowman & Albert, 2018). Also, it is difficult to measure electron density gradients directly and with a high vertical resolution of a few hundred metres in the lower ionosphere, i.e. at the PMWE altitudes. ...
One of the main challenges faced by climate and numerical weather prediction
models is the scarcity of observations in the middle atmosphere that impairs the accuracy of the mesospheric and stratospheric representation. In this thesis, ground-based observations of infrasound waves are exploited to address the need for increased observations in the middle atmosphere. A set of probing approaches both for small-scale and large-scale dynamics is explored.
The velocity spectral analysis is applied to observations of ocean-generated infrasound waves, or microbaroms, to estimate the directional distribution of microbarom soundscapes as a function of time. An advantage of this approach is the
ability to compare microbarom radiation and propagation models against observations in all directions simultaneously. The detected inconsistencies can be used to flag biases in the atmospheric models used when simulating the microbarom
propagation. It is suggested that further focusing of these biases has potential to
enhance the representation of stratospheric dynamics in atmospheric models via
infrasound data assimilation.
The vespa analysis is also employed in a later study to examine the role of ocean-generated infrasound in the generation of polar mesosphere winter echoes observed by a mesosphere-stratosphere-troposphere radar in Sweden. Four mechanisms, each supported by the infrasound analysis, are proposed to explain these radar echoes whose origins are not fully understood.
Observations of ocean-generated infrasound at three high-latitude infrasound arrays are utilized to characterize the circumpolar stratospheric circulation. The approach is based on training a stochastics-based machine learning model to map
between the time series of infrasound observations and the zonal-mean zonal wind
in the polar cap 60◦ −90◦ at the 1 hPa (around 50 km altitude). Based on two
validation years, it is demonstrated that using a combination of infrasound observations and machine-learning opens the opportunity to provide near real-time
diagnostics of the circumpolar stratospheric circulation.
The presence of gravity-wave signatures in ground-based infrasound observations
is demonstrated on a large and consistent dataset of explosion-generated signals
detected in the shadow zone. The effective sound-speed fluctuations in a layer of
infrasound backscattering are retrieved, and their vertical wavenumber spectra are
associated with the ”universal” saturated spectrum of atmospheric gravity waves.
Comparisons to wind measurements by a medium-frequency radar located nearby
show a good agreement and suggest that infrasound can provide a complementary
technique to extend the observational range of atmospheric gravity-wave scales.
... The advantage of using such platforms is their ability to monitor regions of Earth that are inaccessible to other sensing modalities, e.g., oceans [13], and to directly probe acoustic propagation channels [14]. Moreover, it has been shown that balloon borne platforms are subject to relatively low local noise [12,15,16], allowing for better signal detection compared to surface-based sensors, especially for weak signals. Some examples of the signals captured by airborne sensing platforms include earthquakes [17,18], volcanoes [19], and chemical explosions [12]. ...
... More recently, there has been an effort to utilize balloon-borne infrasound sensing in dedicated observational campaigns with the aim to capture signals from controlled events such as surface chemical explosions. However, because this sensing modality is relatively recent, only very few documented instances of such investigations exist [12,15,21]. Controlled explosion experiments can provide important ground-truth information leveraged toward infrasound signal and source identification, and the development and improvement of detection and propagation algorithms. ...
... When successfully deployed, solar hot air balloons reach buoyancy altitude, float until solar energy starts to dissipate at sunset, and then ev descend. The typical altitude of the neutral buoyancy flight, depending on the pheric conditions is 18-22 km above sea level [15]. ...
In recent years, high-altitude infrasound sensing has become more prolific, demonstrating an enormous value especially when utilized over regions inaccessible to traditional ground-based sensing. Similar to ground-based infrasound detectors, airborne sensors take advantage of the fact that impulsive atmospheric events such as explosions can generate low frequency acoustic waves, also known as infrasound. Due to negligible attenuation, infrasonic waves can travel over long distances , and provide important clues about their source. Here, we report infrasound detections of the Apollo detonation that was carried on 29 October 2020 as part of the Large Surface Explosion Coupling Experiment in Nevada, USA. Infrasound sensors attached to solar hot air balloons floating in the stratosphere detected the signals generated by the explosion at distances 170-210 km. Three distinct arrival phases seen in the signals are indicative of multipathing caused by the small-scale perturbations in the atmosphere. We also found that the local acoustic environment at these altitudes is more complex than previously thought.
... This figure shows that given the atmospheric conditions of the flight, the infrasound waves were more likely to have arrived to the balloon from above after having been reflected by the upper layers of the atmosphere. Fortunately, other methods have been investigated in the literature [5] demonstrating that infrasound sources could be located using balloon-borne infrasound sensors, using several balloons detecting the same event. ...
Investigating Venus, a planet with strong similarities to Earth, is key to understanding our solar system history. However, harsh surface conditions (460°C and 92 atm) prevent the use of long-lasting landers. An alternative is to measure ground seismic events from a high altitude (∼55 km) where Venus presents earthly conditions, via stratospheric infrasound measurements using balloons. Conservation of energy and decrease in air density allow infrasound signals to be amplified making their detection easier at high altitude. DESTINY - Detection of Earthquakes through a STratospheric Infrasound studY - flew on the BEXUS 28 balloon in October 2019. Its aim was to use stratospheric infrasound measurements to locate ground seismic events, as a proof of a concept to study the seismic activity of Venus. This paper briefly describes the design of the experiment needed to achieve this objective. It highlights the success of the experiment in detecting a generated ground seismic event, and concludes on the prospects of conducting this experiment on Venus.
