The IDC Seismic, Hydroacoustic and Infrasound Global Low and High Noise Models

Abstract

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. (2005BOWMAN et al. ( , 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.

Coherent ambient infrasound recorded by the International Monitoring System

“…We compare the PMCC results with raw power spectral density (PSD) [Pa 2 /Hz] curves for each station obtained independently by Brown et al . []. Brown et al .…”

Transient gravity perturbations induced by earthquake rupture

“…This is also illustrated in the figures in Section 3. Measurements of such weak gravity transients are masked by a foreground of seismic noise (Berger et al 2004;Brown et al 2014), which is of the order of 100 nm s −2 between 0.1 Hz and 1 Hz. A novel class of instruments, for example seismically isolated gravity gradiometers (also referred to as gravity strainmeters (Harms et al 2013)), is required to detect these early transients.…”

“…Torsion-bar sensitivities have surpassed 10 −7 Hz −1/2 at 0.1 Hz (Shoda et al 2014). Naturally, work on detector designs needs to be accompanied by careful selection of instrument sites, which can have a big impact on ambient seismic or infrasound fields (Berger et al 2004;Brown et al 2014), and also on the associated gravity noise.…”

Lakes as a Source of Short‐Period (0.5–2 s) Microseisms

“…Power spectral density is measured relative to ground acceleration in decibel (dB) units of 10log 10 (m 2 /s 4 /Hz). The two black curves are the high and low noise models of Peterson (); the green curve is the low noise model of McNamara and Buland (); the two blue curves are the horizontal and vertical low noise models of Berger et al, (); the two red curves are the high and low noise models of Brown et al (). All the spectral models have local minima at periods near 0.8 s.…”