Advances in Operational Processing at the International Data Centre

Abstract

The International Data Centre (IDC) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) Preparatory Commission receives and processes in near-real-time data from the International Monitoring System (IMS), a globally distributed network of seismic, hydroacoustic, infrasound and radionuclide stations. Once completed, the IMS network will comprise 60 infrasound stations of which 49 have been installed and certified as of beginning of 2017 (Fig. 6.1). The infrasound stations are arrays of measurement systems that are sensitive to acoustic pressure variations in the atmosphere in the IMS frequency band between 0.02 and 4 Hz. The array configurations include 4–15 elements, with typical designs of 4–8 elements, and with apertures between 1 and 3 km following IMS requirements (Marty 2018; Christie and Campus 2010). After a design and development phase of more than 10 years, the IDC automatic processing system and interactive analysis are fully operational for infrasound technology since February 2010. After reception, storage and referencing in the IDC database, the station data are automatically processed individually (e.g. the station processing stage) (Brachet et al. 2010). Based on the results of the station processing the network processing is initiated to form events with all three waveform technologies. The event information is then reported in IDC products (or bulletins) referred to as Standard Event Lists (SELs). Since 2010, the bulletin production deadlines have been revised and accommodate late arriving data and the signal propagation times for all waveform technologies (Coyne et al. 2012). The final automatic bulletin containing infrasound signals associated to waveform events is the SEL3, which is reviewed by IDC analysts. The result of the interactive review process is the Late Event Bulletin (LEB) on which event definition criteria are applied to produce the Reviewed Event Bulletin (REB). The REB is the final waveform product of the IDC and currently, during provisional operations, the target timeline for publishing the REB is within 10 days of real time. After Entry Into Force (EIF) of the Treaty, the target timeline is reduced to 48 h. Specialized software has been developed for every processing stage at the IDC in order to improve signal-to-noise ratio, detect infrasound signals, categorize and identify relevant detections, form automatic events and perform interactive review analysis. For the period 2010–2017, thousands of waveform events containing infrasound associations appear in the IDC bulletins, and in particular in the REB and the LEB (Late Event Bulletin). This demonstrates the sensitivity of the IMS infrasound component and the IDC ability to globally monitor the infrasound activity. The unique information gathered by the IMS systems have been widely used for civil and scientific studies and have resulted in numerous publications on meteor impacts such as the largest ever infrasound recorded event that is the Chelyabinsk meteor in February 2013 (Brown 2013; Pilger et al. 2015; Le Pichon et al. 2013; Pilger et al. 2019) as well as other observed fireballs and meteors (Marcos et al. 2016; Caudron et al. 2016; Silber and Brown 2019), on powerful volcanic eruptions (Matoza et al. 2017, 2019), on controlled explosions (Fee et al. 2013), on announced underground nuclear test by the Democratic People’s Republic of Korea (DPRK) (CTBTO 2013b, 2017b; Che et al. 2009, 2014) or on atmospheric dynamic research (Le Pichon et al. 2015; Blanc et al. 2019), on characterizing the infrasound global wavefield (Matoza et al. 2013; Ceranna et al. 2019), or on gravity waves study (Marty et al. 2010; Chunchuzov and Kulichkov 2019; Marlton et al. 2019) that could lead to deriving a space and time-varying gravity wave climatology (Drob 2019).