Infrasound Signals Research Articles

A Single Array Approach for Infrasound Signal Discrimination from Quarry Blasts via Machine Learning

Since various phenomena produce infrasound, including both man-made and natural sources, the ever-growing dataflow demands automatic processes via machine learning for signal classification. In this study, we demonstrate a single array approach at the Piszkés-tető (PSZI) infrasound array. Our dataset contains nearly 14,000 manually categorized infrasound detections, processed with the progressive multi channel correlation (PMCC) algorithm from three different sources, such as quarry blasts, storms and signals from a power plant. The dataset was split into a training, a validation and a test subset. Time and frequency domain features as well as PMCC-related features were extracted. Three additional PMCC-related features were constructed in a way to measure the similarity between detections and to be used in single array monitoring. Two different classifiers, support vector machine and random forest, were used for training. Training was performed with three-fold cross validation with grid search. The classifiers were tuned on the training and validation set using the f1 metric (harmonic mean of positive predictive value and true positive rate). Training, validation and testing were performed with and without our three new features that measure similarity between the detections in order to assess their importance in single array monitoring. The selected classifiers reached f1 scores between 0.88 and 0.93. Our results show a promising step toward automatic infrasound event classification.

Seismoacoustic Analysis of the 7 July 2011 Abadan, Turkmenistan, Explosions

ABSTRACT On 7 July 2011, a series of accidental explosions occurred in the town of Abadan, Turkmenistan. The explosions were observed at local distances (11 and 23 km) at the International Monitoring System (IMS) seismic array, GEYT, and at the Central Asian Cross-border Network (CAREMON), seismic station, ASHT. A total of 30 individual seismic events could be identified. IMS infrasound arrays also observed these explosions at longer ranges, for example, from 1374 km (I31KZ, Kazakhstan) to 4307 km (I48TN, Tunisia). These local and long-range observations allow us to compare yields estimated from the seismic data, 0.05–45 tonnes (trinitrotoluene [TNT] equivalent; using P-wave and Rg amplitude relationships) to those estimated from the infrasound data, 4–90 tonnes (using the dominant period). Given the long propagation distances to the closest IMS infrasound arrays, the signal durations are long and individual events in the series cannot be identified in the infrasound signals. Comparison of the seismic and infrasonic yield estimates suggests that the infrasonic dominant periods are likely associated with the largest explosions in the series. In addition to the seismic arrivals observed locally, air-to-ground coupled waves exhibiting downward first motions consistent with an initial positive blast overpressure are also observed at both GEYT and ASHT. The peak-to-peak amplitude of the air-to-ground coupled waves increases with increasing yield, whereas the period of these signals is yield independent. These amplitude observations suggest that air-to-ground coupled arrivals could be better exploited within event analyses and provide a further constraint upon yield. Fully exploiting these events of opportunity, that have multiphenomenology observations, will help to further improve our understanding of how energy from near-surface explosions partitions into the ground and atmosphere and, therefore, improve our understanding of future events.

Development of balloon-based seismology for venus through earth-analog experiments and simulations

Balloon-based seismology through the study of low-frequency seismo-acoustic signals (infrasound) has gained acceptance as a viable way to study seismic activity on Venus. Balloon-based barometers have the potential to detect and characterize atmospheric waves launched by venusquakes and volcanic eruptions while offering substantially longer instrument lifetimes in the Venus middle atmosphere, where temperature and pressure are significantly more benign (0–100°C, ∼1 atm) as compared to the surface (>460 °C, ∼90 atm). One of the major challenges in performing balloon-based seismology on Venus is the absence of ground-truth data for event identification and discrimination. To address this challenge, our activities are aimed at building a catalog of terrestrial balloon-recorded infrasound signals of geophysical provenance, using which signal predictions can be extended to Venus and the detectability of events can be analyzed. We will highlight our recently concluded Balloon-based Acoustic Seismology Study (BASS) flight campaign, which served as Earth-analog experiments for Venus balloon-based seismology. Data collected were used to validate seismo-acoustic simulation tools, which are being expanded to include the Venus atmosphere. These tools will used to generate predictions of infrasound signals from geophysical events on Venus. We will also provide perspective on directions for future instrument development for Venus balloon flights.

Decrease in volcano jet noise peak frequency as crater expands

Volcanic jet noise is the sound, often <20 Hz and termed infrasound, generated by momentum-driven fluid flow through a volcanic vent. Assuming the self-similarity of jet flows and audible jet noise extends to infrasonic volcanic jet noise, the Strouhal number, St, connects frequency changes to those in jet length (expanded jet diameter) and/or velocity scale (jet velocity). We examine the infrasound signals from the June 2019 eruptions of Raikoke, Kuril Islands and Ulawun, Papua New Guinea volcanoes with changes in crater geometry. We use data from the International Monitoring System infrasound network and pre- and post-eruption satellite data (PlanetScope imaging). We observe a decrease in infrasound peak frequency during the transition to a more intense phase, which remains through the end of both eruptions. With the PlanetScope data, we measured a crater area increase of ∼50 000 m2 at Raikoke and ∼31 000 m2 at Ulawun. We use crater diameter as a proxy for expanded jet diameter. Our analysis suggests that the increases in crater diameter alone cannot account for the decreases in peak frequency for a constant St. This suggests the jet velocity also increased, which fits satellite data, and or the fluid properties (e.g., particle loading, nozzle characteristics, etc.) changed. This is reasonable as the eruptions intensified, which likely involved an increase in jet velocity and erosion of the crater walls. This is the first study to corroborate the decrease in infrasound peak frequency with documented increase in crater area.

Dynamics of the December 2020 Ash‐Poor Plume Formed by Lava‐Water Interaction at the Summit of Kīlauea Volcano, Hawaiʻi

AbstractOn 20 December 2020, after more than 2 years of quiescence at Kīlauea Volcano, Hawaiʻi, renewed volcanic activity in the summit crater caused boiling of the water lake over a period of ∼90 min. The resulting water‐rich, electrified plume rose to 11–13 km above sea level, which is among the highest plumes on record for Kīlauea. Although conventional models would infer a high mass flux from explosive magma‐water interaction, the plume was not associated with an infrasound signal indicative of “explosive” activity, nor did it produce a measurable ash‐fall deposit. We use multisensor data to characterize lava‐water interaction and plume generation during this opening phase of the 2020–21 eruption. Satellite, weather radar, and eyewitness observations revealed that the plume was rich in water vapor and hydrometeors but transported less ash than expected from its maximum height. Volcanic lightning flashes detected by ground‐based cameras were confined to freezing altitudes of the upper cloud, suggesting that the ice formation drove the electrification of this plume. The low acoustic energy from lava‐water interaction points to a weakly explosive style of hydrovolcanism. Heat transfer calculations show that the lava to water heat flux was sufficient to boil the lake within 90 min. Limited mixing of lava and water inhibited major steam explosions and fine fragmentation. Results from one‐dimensional plume modeling suggest that the models may underpredict plume height due to overestimation of crosswind air‐entrainment. Our findings shed light on an unusual style of volcanism in which weakly explosive lava‐water interaction generated an outsized plume.

Seismoacoustic Coupled Signals from the 11 July 2020 Ms 5.1 Tangshan, China, Earthquake

ABSTRACT The Ms 5.1 Tangshan earthquake that occurred on 11 July 2020 was recorded by the infrasound array DQS at a source-to-receiver distance of 196 km and an azimuth of 278°. Relatively high-apparent velocity, celerity of epicenter infrasound, and propagation modeling indicate a stratospheric arrival. The backprojection of the epicentral infrasound detection delineates a northeast direction-extended infrasound radiation region with a long axis of about 57 km and a short axis of about 28 km, which is in good agreement with the fault rupture direction. The robustness of the infrasound radiation source location is also tested. The consistency between the spatial distribution of the radiation source and the epicenter confirms that the extended radiating zone around the epicenter excited infrasound signals lasting 2.5 min at a distance of 196 km. A comparison between the backprojected sound pressure level and peak surface pressure derived from measured seismic ground motions shows some disagreement, which may involve propagation path and/or topography around the epicenter. Therefore, these factors should be taken into account when locating the sources of infrasound and estimating the distribution of ground motion. This study shows the ability of infrasound arrays to detect, locate, and research moderate earthquakes and help reconstruct the seismoacoustic coupling in the source region and fault rupture. Moreover, the complexity of the infrasound radiation source and seismoacoustic coupling mechanism is recognized. It is expected that infrasonic observations of moderate earthquakes will increase with the number of infrasound arrays deployed worldwide. Our study is also helpful to the scientific design and optimal layout of infrasound monitoring systems, which will allow for the detection of earthquakes in addition to explosive sources.

Modelling and validation of defects on infrasound wind-noise-reduction pipe systems.

Infrasound signals are detectable from many different sources, such as earthquakes and man-made explosions. Wind-generated turbulent noise can mask incoming infrasound signals; however, pipe-array wind-noise-reduction systems (WNRSs) have been designed to reduce the level of noise in the observed pressure time series. Given that the arrival times of the signals need to be well-known to calculate the source back azimuth and trace velocity, the response of the WNRS must be known in magnitude and phase. Previous work has been performed to optimize these systems and effectively model them. The goal of this research is to determine the effects of different defects which may occur during normal operation in typical field-experiment conditions. The models were extended to include the effects of defective systems, such as blockages or leaks. It was found that these models could effectively recreate the responses observed in an experimental setting, and several different defects were tested and are summarized in this paper.

Measurement and characterization of infrasound waves from the March 25, 2023 thunderstorm at the near equatorial

<abstract> <p>Thunderstorm activity on March 25, 2023 provided a unique opportunity to study the mechanism of lightning events on changes in air pressure. In particular, this event made it possible to study changes in air pressure during thunderstorms using various instruments. This paper presented comprehensive results of infrasound, satellite data, weather radar and weather measurements at the ground during the storm. Observations of lightning events were confirmed using observational data from the International Space Station's Lightning Imaging Sensor (ISS LIS). This work estimated three spectral percentile values on infrasonic sensor data, time series interpolation of standard meteorology profiles, weather radar reflectivity and total radiant energy of lightning from ISS LIS observations during the day and night periods. As a result, during the investigation, it was seen that the recorded infrasound signal in the 0.6–0.8 Hertz (Hz) range was contaminated by background environmental noise, but in the 1–3 Hz band range it was consistent with the appearance of storms that produce high energy blows. Infrasound detection and electromagnetic lightning detection show good correlation up to a distance of 100 km from the infrasonic station. During a thunderstorm, the ISS LIS flight directly above the observation site detected more than 2,000 lightning events. In addition, the application of lightning detection from several independent instruments can provide a complete picture of the observed event.</p> </abstract>

Study on Frequency Spectrum Characteristics and Attenuation Law of Pe Pipeline Leakage Infrasound Signal

Study on Frequency Spectrum Characteristics and Attenuation Law of Pe Pipeline Leakage Infrasound Signal

Temporal variation in the depth of the magma surface at Aso volcano in 2014–2015

Monitoring the depth of the magma surface at open-vent volcanoes can be a practical tool to infer temporal variations in the magma supply during an eruption. We focus on the magmatic eruption of Aso volcano in 2014–2015 to estimate the temporal change in the depth of the magma surface, and show that this needs to be coupled with an understanding of the shallow conduit geometry if it is to be done in a representative manner. The eruption lasted 5 months from November 2014 and ending with a crater floor collapse in May 2015. During the eruption, we recorded seismo-acoustic waveforms related to frequent Strombolian explosions. The infrasound signals show several distinct peak frequencies derived from acoustic resonance inside the vent. We estimate the depth of the magma surface using the time delay of seismo-acoustic signals and the peak frequency of infrasound signals. In addition, the temporal variation in the shape of the conduit is constrained by the overtone frequency of the acoustic resonance. From the beginning of the eruption to early-January 2015, the magma surface was located at a depth of sim 200 m, and the conduit was a cylindrical pipe. Later, between January and February, the magma surface rose to sim 120 m, and the shape of the conduit changed to a conical frustum flaring inside. This finding indicates that the magma was injected into the shallow conduit and that it heated and weakened the conduit wall near the magma surface. Before the cessation of the magmatic eruption, the magma surface dropped by approximately 70 m. This magma drainage and, primarily, the instability of the conduit shape caused the crater floor to collapse. We show the possibility of tracking and assessing the depth of the magma surface and the shallow conduit geometry even with limited seismo-acoustic observations.

Remote Sensing of Infrasound Signals of the “Voice of the Sea” during the Evolution of Typhoons

The article presents summarized results of the study of registered periods of microseisms of the “voice of the sea” infrasound oscillations, generated due to the influence of wind of tropical cyclones (typhoons) passing in the Sea of Japan. We compared the recorded signals and how they correspond to the microseismic background in the wind wave range. Using satellite monitoring data, we verified and identified the groups of cyclones that excite the “voice of the sea” microseisms with approximately the same characteristics. We found that the bandwidth of the “voice of the sea” range and its central frequency, with the maximum amplitude in this frequency range, are approximately the same for typhoons (cyclones) propagating along the same routes. Wind speed also determines the central frequency of the “voice of the sea” range for a particular typhoon (tropical cyclone) propagation route.

Earth’s Upper Crust Seismically Excited by Infrasound from the 2022 Hunga Tonga–Hunga Ha’apai Eruption, Tonga

AbstractRecords of pressure variations on seismographs were historically considered unwanted noise; however, increased deployments of collocated seismic and acoustic instrumentation have driven recent efforts to use this effect induced by both wind and anthropogenic explosions to invert for near-surface Earth structure. These studies have been limited to shallow structure because the pressure signals have relatively short wavelengths (<∼300 m). However, the 2022 eruption of Hunga Tonga–Hunga Ha’apai (also called “Hunga”) volcano in Tonga generated rare, globally observed, high-amplitude infrasound signals with acoustic wavelengths of tens of kilometers. In this study, we examine the acoustic-to-seismic coupling generated by the Hunga eruption across 82 Global Seismographic Network (GSN) stations and show that ground motion amplitudes are related to upper (0 to ∼5 km) crust material properties. We find high (>0.8) correlations between pressure and vertical component ground motion at 83% of the stations, but only 30% of stations show this on the radial component, likely due to complex tilt effects. We use average elastic properties in the upper 5.2 km from the CRUST1.0 model to estimate vertical seismic/acoustic coupling coefficients (SV/A) across the GSN network and compare these to recorded observations. We exclude many island stations from these comparisons because the 1° resolution of the CRUST1.0 model places a water layer below these stations. Our simple modeling can predict observed SV/A within a factor of 2 for 94% of the 51 non-island GSN stations with high correlations between pressure and ground motion. These results indicate that analysis of acoustic-to-seismic coupling from the eruption could be used to place additional constraints on crustal structure models at stations with collocated seismic and pressure sensors. Ultimately, this could improve tomographic imaging models, which rely on methods that are sensitive to local structure.

Remote Monitoring of Mediterranean Hurricanes Using Infrasound

Mediterranean hurricanes, or medicanes, are tropical-like cyclones forming once or twice per year over the waters of the Mediterranean Sea. These mesocyclones pose a serious threat to coastal infrastructure and lives because of their strong winds and intense rainfall. Infrasound technology has already been employed to investigate the acoustic signatures of severe weather events, and this study aims at characterizing, for the first time, the infrasound detections that can be related to medicanes. This work also contributes to infrasound source discrimination efforts in the context of the Comprehensive Nuclear-Test-Ban Treaty. We use data from the infrasound station IS48 of the International Monitoring System in Tunisia to investigate the infrasound signatures of mesocyclones using a multi-channel correlation algorithm. We discuss the detections using meteorological fields to assess the presence of stratospheric waveguides favoring propagation. We corroborate the detections by considering other datasets, such as satellite observations, a surface lightning detection network, and products mapping the simulated intensity of the swell. High- and low-frequency detections are evidenced for three medicanes at distances ranging between 250 and 1100 km from the station. Several cases of non-detection are also discussed. While deep convective systems, and mostly lightning within them, seem to be the main source of detections above 1 Hz, hotspots of swell (microbarom) related to the medicanes are evidenced between 0.1 and 0.5 Hz. In the latter case, simulations of microbarom detections are consistent with the observations. Multi-source situations are highlighted, stressing the need for more resilient detection-estimation algorithms. Cloud-to-ground lightning seems not to explain all high-frequency detections, suggesting that additional sources of electrical or dynamical origin may be at play that are related to deep convective systems.

Lava fountain jet noise during the 2018 eruption of fissure 8 of Kīlauea volcano

Real-time monitoring is crucial to assess hazards and mitigate risks of sustained volcanic eruptions that last hours to months or more. Sustained eruptions have been shown to produce a low frequency (infrasonic) form of jet noise. We analyze the lava fountaining at fissure 8 during the 2018 Lower East Rift Zone eruption of Kīlauea volcano, Hawaii, and connect changes in fountain properties with recorded infrasound signals from an array about 500 m from the fountain using jet noise scaling laws and visual imagery. Video footage from the eruption reveals a change in lava fountain dynamics from a tall, distinct fountain at the beginning of June to a low fountain with a turbulent, out-pouring lava pond surrounded by a tephra cone by mid-June. During mid-June, the sound pressure level reaches a maximum, and peak frequency drops. We develop a model that uses jet noise scaling relationships to estimate changes in volcanic jet diameter and jet velocity from infrasound sound pressure levels and peak frequencies. The results of this model indicate a decrease in velocity in mid-June which coincides with the decrease in fountain height. Furthermore, the model results suggest an increase in jet diameter, which can be explained by the larger width of the fountain that resembles a turbulent lava pond compared to the distinct fountain at the beginning of June. The agreement between the infrasound-derived and visually observed changes in fountain dynamics suggests that jet noise scaling relationships can be used to monitor lava fountain dynamics using infrasound recordings.

The Redmond Salt Mine Monitoring Experiment: Observations of Infrasound Resonance

ABSTRACT From October 2017 to July 2019, we collected seismic recordings of nighttime mining explosions occurring at Redmond Salt Mine. In addition to seismic data, infrasound recordings of the explosions were collected from October 2017 to June 2018. Mine operators provided logs of explosion locations during the period from May 2018 to November 2018, along with a detailed survey of the mine structure. Seismic signals from these explosions exhibit a very complex character resulting from the heterogeneous subsurface of the region. We were able to cluster the observed seismic waveforms into several groups based on waveform similarity, which were then associated with specific regions of active mining using the operator logs. Two of these clusters were associated with several explosive events that generated infrasound easily detected out to 20 km. Because all these events occurred at night, the observed similarity of the infrasound waveforms across all the stations may result from the presence of an inversion layer that traps acoustic energy near the surface. Fully understanding the influence of atmospheric and meteorological conditions on the propagation of these infrasound signals is not possible without additional surveys. However, the recorded infrasound signals exhibit a harmonic structure that appears to result from acoustic reverberations within the mine tunnels. Application of a simple model to explain these results gives a factor of two agreement between the actual and estimated dimension of a mine tunnel whose southern end is open to the atmosphere. The observation of harmonic infrasound signals highlights the increased usefulness of infrasound in monitoring at local distances, relative to monitoring at farther offsets. Although these signals cannot be reliably recorded, presumably due to the requirement of a relatively simple atmosphere at the time of recording, we nonetheless encourage the routine collection of infrasound data in local monitoring applications.

Long range infrasound monitoring of Yasur volcano

The atmospheric injection of gas and material produced by an explosive volcanic eruption determines a rapid compression of the atmosphere, which subsequently propagates as longitudinal elastic waves (sound). The size of the source, generally greater than tens of meters, and its duration, longer than a few seconds, result into an emitted signal that is particularly rich in low frequencies (f < 20 Hz), thus determining an efficient infrasound radiation. Thanks to the low spectral content and the reduced attenuation in the atmosphere, infrasound is capable of propagating for very large distances.In this study we show how the infrasonic monitoring at regional distances (> 100 km) is efficient in recording and characterizing volcanic events. For the purpose of our study, infrasound signal radiated from Yasur volcano (Tanna Island, Vanuatu) was studied for a period of twelve years (January 2008 – December 2019). Signals from Yasur were registered at a source-to-receiver distance of 400 km by the IS22 infrasound array, located in New Caledonia, part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS). The predominantly explosive Strombolian activity of this volcano makes it a perfect subject to be studied by infrasound technology. Detections of volcanic infrasound are modulated according to the seasonal variation of stratospheric winds and corrected for attenuation accounting for real atmospheric specification between the source and the receiver to retrieve the pressure at the source. Next, they are used to evaluate long-term (yearly) and short term (hourly) variations of activity over the period of analysis. Results are compared with thermal anomalies recorded by the MODerate resolution Imaging Spectroradiometer (MODIS) installed on NASA's Terra and Aqua satellites.We show that even at regional distances (400 km) it is possible to follow the long term (yearly) fluctuations of ordinary explosive activity during periods of optimal propagation of infrasonic waves in the atmosphere. In addition, we show that the time resolution retrieved from the signal analysis allows to follow variations of volcanic activity at hourly time scale, thus representing a valuable source of information, in particular in areas where local geophysical observations are missing.

Application of wavelet synchrosqueezed transforms to the analysis of infrasound signals generated by wind turbines.

The issues reported in this article concern the development of methods applied for measurement, processing, and analysis of infrasound signals generated in association with the operation of wind farms. In particular, the discussion involves the results of the analysis using synchrosqueezed wavelet transforms of infrasound noise emitted by a 2 MW wind turbine that have been recorded during its operation in actual conditions. To record infrasound signals, a wireless measurement system was used, consisting of a base station and three synchronized mobile recording stations. To identify the wavelet structures with the highest ratio of energy, the synchrosqueezed wavelet transforms were used, and the courses of six time runs representing instantaneous frequencies were determined. Application of this approach enables the selection of energy-dominant waveforms from the time-frequency images, whose assessment can be performed mainly in terms of qualitative measures. Application of the synchrosqueezed wavelet transform is an effective tool for the purposes of detection and selection in the designated wavelet structures for the recorded infrasound dominant frequencies for which the carried energy ranges have the highest value.

Infrasonic gliding reflects a rising magma column at Mount Etna (Italy)

Infrasound is increasing applied as a tool to investigate magma dynamics at active volcanoes, especially at open-vent volcanoes, such as Mt. Etna (Italy), which are prodigious sources of infrasound. Harmonic infrasound signals have been used to constrain crater dimensions and track the movement of magma within the shallow plumbing system. This study interprets the remarkable systematic change in monotonic infrasound signals preceding a lava fountaining episode at Mt. Etna on 20 February 2021. We model the changing tones (0.7 to 3 Hz fundamental frequency) as a rise in the magma column from 172 ± 25 m below the crater rim to 78 ± 8 m over the course of 24 h. The infrasonic gliding disappears approximately 4 h before the onset of lava fountaining as the magma column approaches the flare of the crater and acoustic resonance is no longer supported. The featured 20 February event was just one of 52 lava fountain episodes that occurred at Mt. Etna over the course of 9 months in 2021 and was the only lava fountain episode where dramatic gliding was observed as a subsequent partial collapse of the crater prevented future resonance. The results presented here demonstrate that analysis of infrasonic gliding can be used to track the position of the magma free surface and hence may provide information on the processes taking place within the plumbing system before eruptive activity.

Evidence for Short Temporal Atmospheric Variations Observed by Infrasonic Signals: 2. The Stratosphere

AbstractThis study uses infrasound detections from a repetitive source to estimate the effect of the atmosphere's temporal variability on infrasound. While a previous paper focused on infrasound propagation through the troposphere to a distance of 54 km, this study uses stratospheric returns detected 256 km from the source. Based on source‐receiver pairs, the empirical Green's function is calculated every 20 s for 52 events; these allow generating a set of synthetic signals where variations are ascribed to variation in the atmosphere. In addition, observations are compared with numerical simulation results based on realistic atmospheric conditions. Results show that variations of stratospheric infrasound signals are observed over timescales ranging from tens of seconds to minutes and have dominant periods ranging from tens to hundreds of seconds. These results motivate using infrasound to probe short temporal changes in the middle atmosphere and study their underlying phenomena.

On the potential use of infrasound for tornado detection and monitoring

The notion that tornadoes emit an infrasonic signal that can be detected from great distances; and thus be used to aid in the detection, monitoring, and potentially tracking of active tornadoes; has been discussed for decades. To test this notion, we deployed a network of infrasound sensor arrays in northern Alabama for the 2017, 2018, and 2019 tornado seasons. Infrasound propagation is complicated by vertical temperature gradients and wind shear. Efficient propagation depends on ducts caused by positive temperature and wind speed gradients. Infrasound signal detection depends on a signal arriving at the detection array with amplitude larger than the turbulent pressure amplitudes (wind noise) in the neighborhood of the array. Focusing on the 1 Hz to 10 Hz frequency band, we show that from each tornado that passed through northern Alabama during that period for which propagation and wind nose analysis suggested that a signal should be detected, a signal was detected. To make a truly convincing argument that the observed signals are produced by active tornadoes two things are needed. One needs to demonstrate that storms from which no tornadoes were spawned do not produce such signals and one must show that there is a physical mechanism related directly to tornadoes through which the infrasound is emitted. We will report on progress on both these fronts.