Abstract
The International Data Centre (IDC) in Vienna, Austria, is determining, as part of automatic processing, sensor noise levels for all seismic, hydroacoustic, and infrasound (SHI) stations in the International Monitoring System (IMS) operated by the Provisional Technical Secretariat of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Sensor noise is being determined several times per day as a power spectral density (PSD) using the Welch overlapping method. Based on accumulated PSD statistics a probability density function (PDF) is also determined, from which low and high noise curves for each sensor are extracted. Global low and high noise curves as a function of frequency for each of the SHI technologies are determined as the minimum and maximum of the individual station low and high noise curves, respectively, taken over the entire network of contributing stations. An attempt is made to ensure that only correctly calibrated station data contributes to the global noise models by additionally considering various automatic detection statistics. In this paper global low and high noise curves for 2010 are presented for each of the SHI monitoring technologies. Except for a very slight deviation at the microseism peak, the seismic global low noise model returns identically the Peterson (1993) NLNM low noise curve. The global infrasonic low noise model is found to agree with that of Bowman et al. (2005, 2007) but disagrees with the revised results presented in Bowman et al. (2009) by a factor of 2 in the calculation of the PSD. The global hydroacoustic low and high noise curves are found to be in quantitative agreement with Urick’s oceanic ambient noise curves for light to heavy shipping. Whale noise is found to be a feature of the hydroacoustic high noise curves at around 15 and 25 Hz.
Highlights
The Provisional Technical Secretariat for the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization is tasked with establishing the verification regime for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) that, upon Entry Into Force (EIF), bans the detonation of nuclear devices in any environment
The International Data Centre processes in near real time data received from the International Monitoring System (IMS) stations, subsequently generating several event bulletins for the benefit of the States Parties that are signatories to the Treaty
Station ambient noise conditions are being represented by the power spectral density (PSD), which provides a measure of the power contained in the signal at each frequency
Summary
The Provisional Technical Secretariat for the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization is tasked with establishing the verification regime for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) that, upon Entry Into Force (EIF), bans the detonation of nuclear devices in any environment. The framework of the verification regime is the global network of 337 seismic, hydroacoustic, infrasound, and radionuclide stations that form the International Monitoring System. Station ambient noise conditions are being represented by the power spectral density (PSD), which provides a measure of the power contained in the signal at each frequency. Determining both single station and network low and high noise models becomes a straightforward procedure when station ambient noise information is routinely accessible. The purpose of this paper is to present the inferred global low and high noise models for each of the SHI technologies based on data recorded by the IMS network. Care is taken at all stages to ensure both the integrity of the data and the method used to determine the station noise information
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