This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Intellectual Merit
This Major Research Instrumentation-Recovery and Reinvestment project will create a real-time infrasound array whose sensing elements are co-located with the 400 seismic stations in the USArray Transportable Array component of the NSF EarthScope program. This continuously sampled array, of an unprecedented scale, will provide opportunities for groundbreaking and interdisciplinary research in atmospheric acoustics, atmospheric science, and seismology. The array will sample mean values and fluctuations of the surface air pressure with nominal 70 kilometer station spacing, with a dynamic range of about 7 orders of magnitude, and with a sampling frequency of up to 40 Hz. This dense network of infrasound sensors will permit study of the nature of long-range infrasound propagation from regional to continental distances, and study of the sources of infrasound signals, using actual acoustic data, free of concerns about seismic-to-acoustic coupling. The array will not only record signals from a range of sources, it will permit study of propagation from these sources under widely varying atmospheric conditions. These data will be used to test atmospheric models and improve understanding of regional to long range infrasound propagation physics. Continuous monitoring of signals from repeating distant sources provides opportunities to probe high altitude winds, yielding valuable information to validate, tune, and improve global whole-atmosphere numerical weather and climate models. Recording actual pressure variations will aid studies of thermospheric attenuation, assess the utility of algorithms for correcting recorded signal amplitudes for wind effects and provide more data for full-waveform analyses. Atmospheric phenomena that can be studied with unprecedented spatio-temporal coverage include solar and lunar atmospheric tides, upper-level and lower-level jet streams, weather fronts, boundary-layer convection, tornadoes, nocturnal drainage flows, and gravity waves. Simultaneous and continuous observations of atmospheric and seismic noise will facilitate adaptive seismometry, a process analogous to adaptive optics in which the effects of atmospheric loading at the Earth's surface are accounted for in seismic channels to reduce noise at long periods. There also will be serendipitous avenues for research that will not be discovered until the data begin to flow. Real time data delivery capabilities will be utilized to allow open and free data distribution.
Broader Impact
This observatory will provide data for research in atmospheric acoustics, seismology and atmospheric science. As papers result from this dataset, it will be easier for institutions to attract researchers and students interested in conducting research in these areas. This network, and the data it will provide, will broaden the participation in science. It will provide many opportunities for training in data analysis, as well as validating models used in atmospheric science and atmospheric acoustics. It will provide opportunities for increasing the quality of very long-period seismic data for studies of the solid earth, and possibly reducing horizontal noise on seismic records by applying corrections derived from long period barometric data. The managing laboratory has a commitment to supporting the integration of research and education at every academic level. The data from the infrasound array will be made freely available in near real time, without restriction, through an on-line data management system, to everyone inside and outside the scientific community. Science teachers will be able to access data they are interested in and incorporate it into their science curricula. Project scientists will work with "Perspectives on Ocean Science," which is an earth and ocean science speaker series hosted by Birch Aquarium at Scripps Institution of Oceanography, to provide the public with direct access to up-to-date science in a presentation that is specifically designed for a lay audience. "Perspectives on Ocean Science" reaches an audience of almost 15 million viewers.
NSF Earthscope USArray Transportable Array (TA) network is a portable array of approximately 400 sites deployed on a nearly Cartesian grid spanning nearly 2 million square kilometers, with an average inter-station spacing of approximately 70 km. The TA is rolling across the country starting in 2004 and completing the eastern seaboard this year. While the TA network was originally designed with seismic research interests in mind, since early 2010 the network has been upgraded with atmospheric pressure and infrasound monitoring equipment. Essentially all of the approximately 500 stations are now recording atmospheric phenomena in real-time at 40 sps and 1 sps using Setra 278 barometers, VTI SCP1000 MEMS barometric pressure gauges, and NCPA infrasound sensors. The US Array pressure data have several unique characteristics that are allowing us to conduct a rigorous analysis of the spatio-temporal variations in the pressure field on time scales of less than an hour across the eastern United States: each sensor is deployed for roughly 2 years as part of a quasi-regular grid covering an eastward rolling swath of the continental United States and in the future providing coverage over Alaska. The reporting resolution of the raw data is not a limiting factor, i.e., ~.001 hPa. The combination of the gridded array and high temporal frequency of the data provides a spatially and temporally unaliased sampling of the perturbation pressure field for wavelengths greater than ~150 km. Observations will be presented from gust fronts, near misses of tornados at individual stations, and of the mesoscale gravity waves showing the value and utility of the US Array pressure data. The 2011 tornado season provided a unique opportunity for realtime monitoring of tornadoes via combined seismic, surface pressure and infrasound observations. The EF5 tornado that devastated Joplin, Missouri on May 22nd of 2011 also passed through Earthscope’s USArray Transportable Array (TA) network. The Joplin tornado passed approximately 2 km south of station T38A, whose location near the town of Joplin allowed for unique observations of the storm. The TA data until recently have not been used extensively in the atmospheric science community. A collaboration with the MesoWest software development team at the University of Utah in early 2012 led to real-time access to the 1 Hz pressure observations from the US Array beginning in March 2012. Data from all TA pressure observations are now retrieved, stored in a relational database as 5 minute averages, and disseminated routinely as part of MesoWest. The pressure data are transmitted as well to the Meteorological Assimilation Data Ingest System (MADIS), which subsequently passes the observations on to the National Center for Environmental Prediction for assimilation of the data into operational numerical weather prediction models. Procedures are in place in MesoWest to automatically update metadata as sensors are decommissioned on the western boundary of the Transportable Array and later redeployed. In the past, most studies of low-frequency sound in the atmosphere (known as infrasound) has relied on a sparse global network of ~ 100 small infrasound arrays (aperture of 3 km or less). However, this USArray seismo-acoustic project has opened up an entirely new direction for research in this area. Although each infrasound array provides much local information about the infrasound wavefield, we know that the wavefield from any source varies significantly at scales much smaller than the average distance between adjacent arrays. In other words, this network undersamples the infrasound wavefield. The TA seismic network, which was designed for studies of seismic sources and the structure of the Earth’s interior, is also proving very valuable for the study of how infrasound propagates through the atmosphere. Seismometers commonly record acoustic-seismic coupled signals from atmospheric infrasound sources. At a 70 km spacing on a nominal Cartesian grid, the TA samples the infrasound wavefield at a density that is allowing us to make significant advances in our understanding of how infrasound propagates through the constantly changing atmosphere. It has been shown by a number of recent studies that infrasound signals are affected significantly by small-scale heterogeneity in the atmosphere largely due to gravity waves.
