Autocorrelation Infrasound Interferometry

Abstract

Seismic and infrasound multistation ambient‐noise interferometry has been widely used to infer ground and atmospheric properties, and single‐station and autocorrelation seismic interferometry has also shown potential for characterizing Earth structure at multiple scales. We extend autocorrelation seismic interferometry to ambient atmospheric infrasound recordings that contain persistent local noise from waterfalls and rivers. Across a range of geographic settings, we retrieve relative sound‐speed changes that exhibit clear diurnal oscillations consistent with temperature and wind variations. We estimate ambient air temperatures from variations in relative sound speeds. The frequency band from 1 to 2 Hz appears most suitable to retrieve weather parameters as nearby waterfalls and rivers may act as continuous and vigorous sources of infrasound that help achieve convergence of coherent phases in the autocorrelation codas. This frequency band is also appropriate for local sound‐speed variations because it has infrasound with wavelengths of ∼170–340 m, corresponding to a typical atmospheric boundary layer height. After applying array analysis to autocorrelation functions derived from a three‐element infrasound array, we find that autocorrelation codas are composed of waves reflected off nearby topographic features, such as caldera walls. Lastly, we demonstrate that autocorrelation infrasound interferometry offers the potential to study the atmosphere over at least several months and with a fine time resolution.

Evidence for Short Temporal Atmospheric Variations Observed by Infrasonic Signals: 1. The Troposphere

“…Second, infrasound can be used to probe the atmosphere. It has been done by: (1) quantifying atmospheric winds based on back azimuth, apparent velocity, and travel time variations (Assink et al., 2012; Blixt et al., 2019; Diamond, 1964), (2) using back azimuth and apparent velocity values as constraints for probabilistic inversion (Assink et al., 2013; Drob et al., 2009; Lalande et al., 2012; Le Pichon et al., 2005; Smets et al., 2016; Vanderbecken et al., 2020; Vera Rodriguez et al., 2020), (3) infrasound ambient noise interferometry (Fricke et al., 2014; Haney, 2009; Ortiz et al., 2021), and (4) assimilation of infrasound data (Amezcua & Barton, 2021; Amezcua et al., 2020).…”

“…Since the atmosphere is dynamic, infrasound propagation conditions are continuously changing. For example, Ortiz et al (2021) observe variations in the atmospheric properties (over several kilometers) over a timescale of 30 min. In addition, atmospheric soundings based on long-range propagation (hundreds of kilometers) show temporal variations in the observed back azimuth and apparent velocity in timescales of hours; these observations also deviate from the predicted values by several degrees and tens of meters per second (Smets et al, 2016;Vanderbecken et al, 2020).…”

Reviewing volcano hazard and risk communications in Ecuador: experiences from a fast-format workshop

“…The most recent notable activity began with the eruptions of Tungurahua and Guagua Pichincha in September and October 1999, respectively, and since then three additional volcanoes (El Reventador, Cotopaxi, Sangay) have erupted in continental Ecuador [Hall and Mothes 2008;Robin et al 2008;Hidalgo et al 2018;Almeida et al 2019;Ortiz et al 2020;Valverde et al 2021]. These volcanoes showed different eruptive styles and eruption durations and led to different impacts on the population: Guagua Pichin-cha's eruption mainly resulted in ashfall on the capital city of Quito and the consequences (especially on the younger population) lasted for a few months [Naumova et al 2007]; Tungurahua's eruption lasted 16 years with explosions that occasionally caused significant ash emissions and pyroclastic density currents (PDC) that impacted local communities in various forms [Few et al 2017]; El Reventador and Sangay volcanoes continue to erupt almost without interruption to this day, with outbursts of explosions and small to medium PDCs and a relatively rapid landscape change [Ortiz et al 2021;Valverde et al 2021]; Cotopaxi volcano's brief reactivation in 2015 lasted for a few months with a paroxysm with a volcano explosivity index (VEI) of 2 and a lowlevel ash plume that caused social distress in nearby (∼14 km) communities [Hidalgo et al 2018;Gomez-Zapata et al 2021]. The high spatial density of active Holocene volcanoes and associated volcanic hazards has impacted pre-Columbian populations [Isaacson and Zeidler 1999;Hall and Mothes 2008;Vallego Vargas 2011;Le Pennec 2013] and continues to impact contemporary populations [Le Pennec et al 2008;Biass et al 2012;Le Pennec et al 2012] in the region.…”

“…Volcano hazard and risk communications in EcuadorAnzieta et al 2021 ited curation/arbitration of content. For instance, the press or other traditional media are somewhat more reliable than social media due to presumed verification of sources; however, it is often much slower and unidirectional compared to social media and there are numerous examples where official information was misrepresented in the press for political or economic gain, resulting in undue panic[Sennert et al 2015;Krippner 2018;Rubin 2018;Williams and Krippner 2019].…”

Autocorrelation Infrasound Interferometry on Mars

“…We use the variations in signal duration and travel time to infer the relative changes of sound-speed, which in turn are related to oscillations of temperature and wind velocity. In terrestrial volcanic, coastal, and in-land settings, Ortiz et al (2021) demonstrated that autocorrelation infrasound interferometry takes advantage of natural ambient noise sources in the frequency band of 1-2 Hz to quantify daily variations of relative soundspeed that can be up to 3% (which is ∼10 times smaller than those observed on Mars). Feasible terrestrial sources of continuous noise in this frequency band are waterfalls and rivers near the infrasound receivers and coherent phases emerging on the autocorrelation of codas are direct waves scattered off nearby topographic features (Ortiz et al, 2021).…”