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Fee D.,University of Alaska Fairbanks | Waxler R.,University of Mississippi | Assink J.,University of Mississippi | Gitterman Y.,Geophysical Institute of Israel | And 8 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

Three large-scale infrasound calibration experiments were conducted in 2009 and 2011 to test the International Monitoring System (IMS) infrasound network and provide ground truth data for infrasound propagation studies. Here we provide an overview of the deployment, detonation, atmospheric specifications, infrasound array observations, and propagation modeling for the experiments. The experiments at the Sayarim Military Range, Israel, had equivalent TNT yields of 96.0, 7.4, and 76.8 t of explosives on 26 August 2009, 24 January 2011, and 26 January 2011, respectively. Successful international collaboration resulted in the deployment of numerous portable infrasound arrays in the region to supplement the IMS network and increase station density. Infrasound from the detonations is detected out to ~3500 km to the northwest in 2009 and ~6300 km to the northeast in 2011, reflecting the highly anisotropic nature of long-range infrasound propagation. For 2009, the moderately strong stratospheric wind jet results in a well-predicted set of arrivals at numerous arrays to the west-northwest. A second set of arrivals is also apparent, with low celerities and high frequencies. These arrivals are not predicted by the propagation modeling and result from unresolved atmospheric features. Strong eastward tropospheric winds (up to ~70 m/s) in 2011 produce high-amplitude tropospheric arrivals recorded out to >1000 km to the east. Significant eastward stratospheric winds (up to ~80 m/s) in 2011 generate numerous stratospheric arrivals and permit the long-range detection (i.e., >1000 km). No detections are made in directions opposite the tropospheric and stratospheric wind jets for any of the explosions. Comparison of predicted transmission loss and observed infrasound arrivals gives qualitative agreement. Propagation modeling for the 2011 experiments predicts lower transmission loss in the direction of the downwind propagation compared to the 2009 experiment, consistent with the greater detection distance. Observations also suggest a more northerly component to the stratospheric winds for the 2009 experiment and less upper atmosphere attenuation. The Sayarim infrasound calibration experiments clearly demonstrate the complexity and variability of the atmosphere, and underscore the utility of large-scale calibration experiments with dense networks for better understanding infrasound propagation and detection. Additionally, they provide a rich data set for future scientific research. Key Points Three large ground-truth infrasound experiments were conducted in 2009 and 2011 Strong wind jets permitted long range detection Atmospheric specifications sufficient for qualitative propagation modeling © 2013. American Geophysical Union. All Rights Reserved.

Matoza R.S.,CEA DAM Ile-de-France | Matoza R.S.,University of California at San Diego | Landes M.,CEA DAM Ile-de-France | Le Pichon A.,CEA DAM Ile-de-France | And 2 more authors.
Geophysical Research Letters | Year: 2013

The ability of the InternationalMonitoring System (IMS) infrasound network to detect atmospheric nuclear explosions and other signals of interest is strongly dependent on stationspecific ambient noise. This ambient noise includes both incoherent wind noise and real coherent infrasonic waves. Previous ambient infrasound noise models have not distinguished between incoherent and coherent components. We present a first attempt at statistically and systematically characterizing coherent infrasound recorded by the IMS. We perform broadband (0.01-5Hz) array processing with the IMS continuous waveform archive (39 stations from 1 April 2005 to 31 December 2010) using an implementation of the Progressive Multi-Channel Correlation algorithm in logfrequency space. From these results, we estimate multi-year 5th, 50th, and 95th percentiles of the RMS pressure of coherent signals in 15 frequency bands for each station. We compare the resulting coherent infrasound models with raw power spectral density noise models, which inherently include both incoherent and coherent components. Our results indicate that IMS arrays consistently record coherent ambient infrasound across the broad frequency range from 0.01 to 5Hz when wind noise levels permit. The multi-year averaging emphasizes continuous signals such as oceanic microbaroms, as well as persistent transient signals such as repetitive volcanic, surf, thunder, or anthropogenic activity. Systematic characterization of coherent infrasound detection is important for quantifying a station's recording environment, signal-to-noise ratio as a function of frequency and direction, and overall performance, which all influence the detection probability of specific signals of interest. © 2013. American Geophysical Union. All Rights Reserved.

Disch C.,Albert Ludwigs University of Freiburg | Dambacher M.,Albert Ludwigs University of Freiburg | Zwerger A.,Albert Ludwigs University of Freiburg | Fauler A.,Albert Ludwigs University of Freiburg | And 3 more authors.
IEEE Transactions on Nuclear Science | Year: 2012

The Freiburg Materials Research Center (FMF) is developing a spectroscopic system with high efficiency and high energy resolution based on (Cd,Zn)Te detectors with coplanar grid (CPG) configuration. Our system features an improved multi-channel analyzer with digital signal processing and a large volume detector stack. Thermoelectric cooling is used to improve energy resolution and maintain detector temperature at a constant value. System performance under laboratory and outdoor conditions is investigated in this paper. © 2012 IEEE.

Koohkan M.R.,ParisTech National School of Bridges and Roads | Koohkan M.R.,French Institute for Research in Computer Science and Automation | Bocquet M.,ParisTech National School of Bridges and Roads | Bocquet M.,French Institute for Research in Computer Science and Automation | And 3 more authors.
Atmospheric Environment | Year: 2012

The International Monitoring System (IMS) radionuclide network enforces the Comprehensive Nuclear-Test-Ban Treaty which bans nuclear explosions. We have evaluated the potential of the IMS radionuclide network for inverse modelling of the source, whereas it is usually assessed by its detection capability. To do so, we have chosen the degrees of freedom for the signal (DFS), a well established criterion in remote sensing, in order to assess the performance of an inverse modelling system. Using a recent multiscale data assimilation technique, we have computed optimal adaptive grids of the source parameter space by maximising the DFS. This optimisation takes into account the monitoring network, the meteorology over one year (2009) and the relationship between the source parameters and the observations derived from the FLEXPART Lagrangian transport model. Areas of the domain where the grid-cells of the optimal adaptive grid are large emphasise zones where the retrieval is more uncertain, whereas areas where the grid-cells are smaller and denser stress regions where more source variables can be resolved.The observability of the globe through inverse modelling is studied in strong, realistic and small model error cases. The strong error and realistic error cases yield heterogeneous adaptive grids, indicating that information does not propagate far from the monitoring stations, whereas in the small error case, the grid is much more homogeneous. In all cases, several specific continental regions remain poorly observed such as Africa as well as the tropics, because of the trade winds. The northern hemisphere is better observed through inverse modelling (more than 60% of the total DFS) mostly because it contains more IMS stations. This unbalance leads to a better performance of inverse modelling in the northern hemisphere winter. The methodology is also applied to the subnetwork composed of the stations of the IMS network which measure noble gases. © 2012 Elsevier Ltd.

Van Der Schaar M.,Polytechnic University of Catalonia | Ainslie M.A.,TNO | Robinson S.P.,National Physical Laboratory United Kingdom | Prior M.K.,CTBTO | Andre M.,Polytechnic University of Catalonia
Journal of Marine Systems | Year: 2014

The growing scientific and societal concerns about the effects of underwater sound on marine ecosystems have been recently recognised through the introduction of several international initiatives, like the International Quiet Ocean Experiment, aimed at measuring the environmental impact of ocean noise on large spatial and temporal scales. From a regulatory perspective, the European Marine Strategy Framework Directive includes noise (and other forms of energy) as one of eleven descriptors of good environmental status of Europe's seas. The directive requires member states to monitor trends in annually averaged sound. The Laboratory of Applied Bioacoustics has developed a software package that measures sound levels and monitors acoustic sources in real-time; this software was used for the LIDO project (www.listentothedeep.com), which originated from the European Seafloor Observatory Network of Excellence (ESONET-NoE; www.esonet-noe.org). The system is currently operating worldwide from several wired and radio-linked observatories. The CTBTO (Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization) has made available years of data from hydroacoustic stations to look for ambient sound trends and to detect cetacean presence. Here, we present the analysis of four CTBTO platforms (located in the Pacific, Atlantic and Indian oceans), covering 42. months of data, intended to detect annual and monthly changes or trends in the ambient sound levels. © 2013 Elsevier B.V.

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