Ronan Le Bras | University of Vienna (original) (raw)

Papers by Ronan Le Bras

Pure and Applied Geophysics

This paper focuses on events linked to controlled underwater explosions of World War 2 (WW2) ordn... more This paper focuses on events linked to controlled underwater explosions of World War 2 (WW2) ordnances which were included in the Reviewed Event Bulletin (REB). Data used for the study were provided by seismic stations of the International Monitoring System (IMS) in 2020. Examined events were triggered by devices of different charge size and took place in several locations in Europe. There were also other, previously detected WW2 ordnance underwater explosions which could be compared to events in 2020. It is shown that these relatively small underwater explosions listed in the REB, with good coupling to the ground, are located by the IMS network within 20 km from the ground truth. Charge size of explosive material was related to event magnitude. Results were compared to magnitudes published for underwater explosions of larger sizes. The conclusion is that an in-water explosion will result in seismic waves with amplitudes equivalent to the amplitudes of seismic waves from an in-groun...

Seismological Research Letters

Examination of the International Monitoring System (IMS) hydroacoustic data recorded during the 1... more Examination of the International Monitoring System (IMS) hydroacoustic data recorded during the 15 January 2022 eruption of the Hunga Tonga–Hunga Ha’apai (HTHH) volcano shows that the in-water hydroacoustic sensors recorded a long-duration (40 min) activity starting before and ending after the paroxysmal HTHH eruption at about 4:15 UTC. The main eruption at 4:15 UTC simultaneously generated low-frequency [0.001–0.05] Hz seismic body waves and large infrasound waves in the atmosphere, as well as a tsunami. The peak-to-peak pressure observed at the closest IMS station, IS22, 1850 km away from the source, was 340 Pa, dwarfing the largest previously observed record for the signal from the Chelyabinsk meteor. The infrasound waves included a Lamb wave containing periods at least up to 2000 s. The Lamb wave and tsunami are well recorded on infrasound and near-shore seismometers. The air wave generated a precursor tsunami ahead of the main tsunami, but we do not observe it on the hydroacous...

The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is ... more The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is exploring methods to enhance the current operational infrasound processing system at the International Data Centre (IDC) for infrasound data recorded by the International Monitoring System (IMS). Several enhancements are under development and are currently being tested. The first enhancement is the incorporation of methods for determining signal amplitude. The following signal amplitudes are being determined for each infrasound detection: peak-to-peak amplitude, root mean squared (RMS) amplitude, and instantaneous amplitude as revealed by the analytic trace via the Hilbert Transform. Initial efforts consider a variety of frequency bands, with the utility in network processing being of primary importance. A second enhancement is the incorporation of station noise characterization in terms of the power spectral density (PSD). This determines the noise field at each station for various time...

Journal of King Saud University - Science, 2022

Page 1. STATUS OF THE MACHINE LEARNING EFFORTS AT THE INTERNATIONAL DATA CENTRE OF THE CTBTO Rona... more Page 1. STATUS OF THE MACHINE LEARNING EFFORTS AT THE INTERNATIONAL DATA CENTRE OF THE CTBTO Ronan J. Le Bras1, Sheila Vaidya2, Jeff Schneider3, Stuart Russell4, and Nimar Arora4 Comprehensive ...

In September 1996, the crew of a three-day marine seismic refraction experiment detonated 141 exp... more In September 1996, the crew of a three-day marine seismic refraction experiment detonated 141 explosions off the coast of Northern Honshu, Japan. The energy released by the explosion sources was eventually recorded by hydrophoness at Wake Island (WAKE) and Point Sur, California (PSUR), some 28 and 71 degrees distant, respectively. We compared the travel-times, amplitudes, and signal-to-noise ratios of the explosion phases with several sets of synthetic detection attributes generated from one-dimensional or two-dimensional hydroacoustic travel time and transmission loss tables. The two-dimensional tables tended to provide more accurate results. For example, the travel time differences at PSUR were -2.8 +- 6.8 sec. using the two-dimensional model whereas the one-dimensional model exhibited differences of -35.5 +- 4.0 sec. All detected phases were classified as either noise, T-phases, or explosion phases. In spite of varying noise backgrounds, 72% of the explosion phases were correctly identified. The hydroacoustic data set helped us evaluate the accuracy of the automatic processing performed at the CMR and validate our modeling of these signals. This modeling should prove useful in preparation of the full deployment of the hydroacoustic International Monitoring System.

SEG Technical Program Expanded Abstracts 1992, 1992

Wavelet transforms allow efficient analysis of signals in one or more dimensions. The signals may... more Wavelet transforms allow efficient analysis of signals in one or more dimensions. The signals may be expressed at different scales of resolution. This provides schemes for compression of informations in image and speech processing. The mathematical framework of wavelet analysis is novel and well grounded in theoretical works and the computation of wavelet transforms is based on an efficient iterative algorithm. This work deals with the use of wavelet transform in the downward continuation problem for acoustic propagation. The operator for a constant velocity layer is expressed using a one-level wavelet transform. The wavelet representation of this operator is sparser than its standard space representation. The different parts of the impulse response wavefield, corresponding to four submatrices of the wavelet space operator are separated and illustrate the dominance of the slowly varying (‘low frequency’) part of the wavefield. Seismic data is often slowly varying as a function of horizontal spatial variables. This suggests that very efficient downward continuation may be obtained by separating seismic wavefields using wavelet analysis.

Seismological Research Letters, 2013

Geophysical …, 2007

... ellipses for the SEL1 event (green dot) and the REB event (red star). The semi-... stations. ... more ... ellipses for the SEL1 event (green dot) and the REB event (red star). The semi-... stations. The resulting set of solutions is shown on the map to the left (green dots) along with the REB solution (red star). It is clear that there is a strong scatter depending on the inclusion or ...

Pure and Applied Geophysics, 2012

Journal of the Acoustical Society of America, 2018

The CTBT International Monitoring System (IMS) is a world-wide network of seismic, infrasound, hy... more The CTBT International Monitoring System (IMS) is a world-wide network of seismic, infrasound, hydroacoustic, and radionuclide stations designed and deployed to detect nuclear explosions. Two of the IMS hydrophone stations, one in the Atlantic Ocean and one in the southern Indian Ocean, recorded signals of unknown nature which originated from the vicinity of the last known location of the San Juan submarine on 15 November 2017. To verify the accuracy of this hydroacoustic event localization, the Argentinian Navy successively deployed a controlled depth charge to the North of the last known position of the submarine. The signals from this source were also detected on the same two IMS hydrophone stations. Several techniques were employed to compare hydroacoustic features in the signals from the 15 November event and the controlled depth charge, including an assessment of spectral energy levels, cepstral analysis, azimuth and arrival time estimation of direct and reflected signals. Thi...

Machine learning projects were conceived in March 2009 as part of the International Scientific St... more Machine learning projects were conceived in March 2009 as part of the International Scientific Studies Project initiative at the Provisional Technical Secretariat of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) and initiated a few months later. Some of the projects are intended to aim at short to medium term operational applications. These include the identification of seismic and hydroacoustic phase names using a large number of features extracted from the waveforms, and the labeling of automatic events as real or false depending again on a large number of features from the automatic events. Concrete research results using International Data Centre (IDC) data are available for these two sets of projects. Seismic phase identification is shown to have the potential to improve its accuracy by 23 %, and the software developed for the project on false events identification has been tested at the IDC and shown to correctly label 80% of the false alarms. Some projects ar...

Since 2009, an initiative to investigate the potential of machine learning methods to improve aut... more Since 2009, an initiative to investigate the potential of machine learning methods to improve automatic data processing at the CTBTO and in particular the recall and accuracy of the automatic bulletins is starting to bear fruit beyond the stage of research and has entered the domain of development and testing with the goal of operational testing for one of the projects (FEI) by the end of 2011. The prospect for FEI is that the tool will comfort analysts in their decision-making process when they make decisions on whether a (mostly smaller) event is real or false, and it is thus an enhancement of the current analysis system. The VISA projects are more ambitious and aim at replacing key components of the processing system. The prototype of the first generation, which aims at replacing the current automatic association tool (GA), is being evaluated on the vDEC collaborative platform of the CTBTO. Results show much improved accuracy using VISA as compared to the SEL3 for the same recall...

: The Provisional Technical Secretariat (PTS) of the Comprehensive Nuclear-Test-Ban Treaty Organi... more : The Provisional Technical Secretariat (PTS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) has been ramping-up the installation of the International Monitoring System (IMS) consisting of a network of seismic, hydroacoustic, infrasound, and radionuclide stations, since its inception in March 1997. Data from this network are automatically processed at the International Data Centre (IDC) to produce, within a few hours, a series of automatic bulletins called the Standard Event Lists (SEL1, SEL2, SEL3). After analyst review and correction as necessary the Reviewed Event Bulletin (REB) is produced. Additional information about characterization of an event as an earthquake or otherwise is also available in the Standard Event Bulletin (SEB) shortly after production of the REB. The Comprehensive Nuclear-Test-Ban Treaty (CTBT) states that the IDC will apply standard event screening criteria to each event formed. The objective of this process is to filter out events that a...