International Monitoring System Research Articles

Increasing the detection sensitivity of the Radionuclide Aerosol Sampler/Analyzer using a cosmic veto system

Abstract Different configurations of a cosmic veto system have been evaluated for the Radionuclide Aerosol Sampler/Analyzer (RASA). The upgrade has the potential to resolve the issue that U.S. International Monitoring System (IMS) radionuclide stations have difficulty meeting the 140Ba Minimum Detectable Concentration (MDC) certification requirement when the natural background radioactivity is high. It also aims to improve the detection sensitivity of the RASA system for other fission and activation products indicative of a nuclear explosion. This proof of principal utilizes a prototype RASA system located at Pacific Northwest National Laboratory (PNNL), and has demonstrated background reductions by up to 11.3% and improvements in the average MDC by up to 7.7%. Recommendations are made for either a 1 or 3 plate configuration, which improves the 140Ba MDC by 5.6% and 7.2% for a blank filter. Whilst elevated 212Pb activity remains problematic, the cosmic veto system provides a practical solution for sensitivity improvement with little design modification of the RASA. It also has value in improving sensitivity and preventing false-positives at remote U.S. IMS station locations where sample transfer for laboratory analysis is logistically difficult.

Combination of infrasound signals and complementary data for the analysis of bright fireballs

The flux densities of meteoroids and asteroids in the intermediate size range (approx. 20 cm – 30 m) impacting the Earth’s Atmosphere still have large uncertainties. There are too few objects of these sizes to be detected with localized fireball networks. Two detection methods that provide a global coverage of fireballs and bolides in this size range are infrasound monitors and space-based satellite sensors. Results from these sensors have large uncertainties specifically what concerns the energy release of the impacting bodies. In this paper a detailed analysis of infrasound data is performed to better understand recorded signals and uncertainties. This will allow to put the analysis and interpretation of infrasound data from impacts on a more solid scientific basis.Atmospheric impacts from large meteoroids or sometimes even asteroids generate infrasound signals which can often propagate over large distances and be registered at infrasound stations. The world-wide network of infrasound stations from the IMS (International Monitoring System) which is operated by the CTBTO (Comprehensive Nuclear-Test-Ban Treaty Organisation, Vienna, Austria) monitors most of the Earth’s Atmosphere and can detect the energy released by meteoroids. Hence, fireball infrasound signals can be used as a very promising information source for fireball research.Nonetheless, the data analysis is very complex and a topic of current discussions and research. In this paper a detailed analysis of the infrasound signals of some fireballs is carried out to be adapted to systematically calculate location, speed, and size or energy of the impacting objects from the infrasound data. Comparisons of other observation methods are also used for this purpose. Moreover, particular attention is paid to uncertainties in the analysis of infrasound data.The infrasound data analysis is part of the NEMO (NEar real-time MOnitoring system) project which started in autumn 2017. It is an information system analysing and combining data from multiple sources ranging from Social Media to infrasound data to monitor the impacts of fireballs on a global scale and to maximize the available scientific information.The infrasound data of the well-studied Chelyabinsk superbolide that exploded over southern Russia in 2013 and the Sulawesi, Indonesia, fireball that was registered in 2009 are reprocessed and the results compared to previous studies.To demonstrate the capacities and advantages of infrasound for the gathering of scientific information two recent fireballs are analysed in detail. These occurred on 08 March 2018 over Washington State (WS), USA, and on 21 June 2018 over the Ozerki region, Russia, respectively. For both fireballs infrasound signals were recorded making it possible to determine the source energy. We derived energies of about EWS=22tTNT and ERussia=2.4ktTNT using a published yield estimation relationship. Combining all available different data sources, which have information on these fireballs, ranging from rain radar to witness reports allowed us to derive a size (diameter) of the entering body in both cases, sWS=0.8m and. sRussia=3.8m.

BDS-3 Time Group Delay and Its Effect on Standard Point Positioning

The development of the BeiDou navigation system (BDS) is divided into three phases: The demonstration system (BDS-1), the regional system (BDS-2) and the global BeiDou navigation system (BDS-3). At present, the construction of the global BeiDou navigation system (BDS-3) constellation network is progressing very smoothly. The signal design and functionality of BDS-3 are different from those of BDS-1 and BDS-2. The BDS-3 satellite not only broadcasts B1I (1561.098 MHz) and B3I (1268.52 MHz) signals but also broadcasts new signals B1C (1575.42 MHz) and B2a (1176.45 MHz). In this work, six tracking stations of the international GNSS monitoring and assessment system (iGMAS) were selected, and 41 consecutive days of observation data, were collected. To fully exploit the code observations of BDS-2 and BDS-3, the time group delay (TGD) correction model of BDS-2 and BDS-3 are described in detail. To further verify the efficacy of the broadcast TGD parameters in the broadcast ephemeris, the standard point positioning (SPP) of all the signals from BDS-2 and BDS-3 with and without TGD correction was studied. The experiments showed that the B1I SPP accuracy of BDS-2 was increased by approximately 50% in both the horizontal and vertical components, and B1I/B3I were improved by approximately 70% in the horizontal component and 47.4% in the vertical component with TGD correction. The root mean square (RMS) value of B1I and B1C from BDS-3 with TGD correction was enhanced by approximately 60%–70% in the horizontal component and by approximately 50% in the vertical component. The B2a-based SPP was increased by 60.2% and 64.4% in the east and north components, respectively, and the up component was increased by approximately 19.8%. For the B1I/B3I and B1C/B2a dual-frequency positioning accuracy with TGD correction, the improvement in the horizontal component ranges from 62.1% to 75.0%, and the vertical component was improved by approximately 45%. Furthermore, the positioning accuracy of the BDS-2 + BDS-3 combination constellation was obviously higher than that of BDS-2 or BDS-3.

The Mount Meron infrasound array: an infrasound array without a noise reduction system

SUMMARYMeasurements of seismo-acoustic events by collocated seismic and infrasound arrays allow for studying the two wavefields that were produced by the same event. However, some of the scientific and technical constraints on the building of the two technologies are different and may be contradicting. For the case of a new station, an optimal design that will satisfy the constraints of the two technologies can be found. However, in the case of upgrading an existing array by adding the complementing technology, the situation is different. The site location, the array configuration and physical constraints are fixed and may not be optimal for the complementing technology, which may lead to rejection of the upgrade. The International Monitoring System (IMS) for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) includes 37 seismic arrays and 51 infrasound arrays. Although the CTBT verification regime is fixed in the treaty, an upgrade of the existing arrays by adding more technologies is possible.The Mount Meron seismic array (MMAI), which is part of the IMS, is composed of 16 sites. Microbarometers were installed at five MMAI sites to form the Mount Meron infrasound array. Due to regulation and physical constraints, it was not possible to relocate the sites nor to install analogue noise reduction filters (i.e. a pipe array). In this study, it is demonstrated that the installation of the MMAI infrasound array is beneficial despite the non-optimal conditions. It is shown that the noise levels of the individual array sites are between the high and median global noise levels. However, we claim that the more indicative measures are the noise levels of the beams of interest, as demonstrated by analysing the microbaroms originated from the Mediterranean Sea. Moreover, the ability to detect events relevant to the CTBT is demonstrated by analysing man-made events during 2011 from the Libya region.

Observing the Oceans Acoustically

Acoustics play a central role in mankind’s interactions with the ocean and the life within. Passive listening to ocean “soundscapes” informs us about the physical and bio-acoustic environment from earthquakes to communication between fish. Active acoustic probing of the environment informs us about ocean topography, currents and temperature, and abundance and type of marine life vital to fisheries and biodiversity related interests. The two together in a multi-purpose network can lead to discovery and improve understanding of ocean ecosystem health and biodiversity, climate variability and change, and marine hazards and maritime safety. Passive acoustic monitoring (PAM) of sound generated and utilized by marine life as well as other natural (wind, rain, ice, seismics) and anthropogenic (shipping, surveys) sources, has dramatically increased worldwide to enhance understanding of ecological processes. Characterizing ocean soundscapes (the levels and frequency of sound over time and space, and the sources contributing to the sound field), temporal trends in ocean sound at different frequencies, distribution and abundance of marine species that vocalize, and distribution and amount of human activities that generate sound in the sea, all require passive acoustic systems. Acoustic receivers are now routinely acquiring data on a global scale, e.g., Comprehensive Nuclear-Test-Ban Treaty Organization International Monitoring System hydroacoustic arrays, various regional integrated ocean observing systems, and some profiling floats. Judiciously-placed low-frequency acoustic sources transmitting to globally distributed PAM and other systems provide: 1) high temporal resolution measurements of large-scale ocean temperature/heat content variability, taking advantage of the inherent integrating nature of acoustic travel-time data using tomography; and 2) acoustic positioning (“underwater GPS”) and communication services enabling basin-scale undersea navigation and management of floats, gliders, and AUVs. This will be especially valuable in polar regions with ice cover. Routine deployment of sources during repeat global-scale hydrographic ship surveys would provide high spatial coverage snapshots of ocean temperatures. To fully exploit the PAM systems, precise timing and positioning need to be broadly implemented. Ocean sound is now a mature Global Ocean Observing System (GOOS) “essential ocean variable”, which is one crucial step toward providing a fully integrated global multi-purpose ocean acoustic observing system.

How Can the International Monitoring System Infrasound Network Contribute to Gravity Wave Measurements?

Gravity waves (GWs) propagate horizontally and vertically in the atmosphere. They transport energy and momentum, and therefore GWs can affect the atmospheric circulation at different altitude layers when dissipating. Thus knowledge about the occurrence of GWs is essential for Numerical Weather Prediction (NWP). However, uniform networks for covering GW measurements globally are rare, especially in the troposphere. It has been shown that an infrasound station of the International Monitoring System (IMS) infrasound network is capable of measuring GWs at the Earth’s surface. The IMS was deployed for monitoring the atmosphere to verify compliance with the Comprehensive Nuclear-Test-Ban-Treaty. In this study, the Progressive Multi-Channel Correlation Method (PMCC) is used for re-processing up to 20 years of IMS infrasound recordings in order to derive GW detections. For this purpose, two alternative PMCC configurations are discussed, covering GW frequencies equivalent to periods of between 5 min and 150 min. These detections mainly reflect sources of deep convection, particularly in the tropics. At mid-latitudes, coherent wind noise more often produces spurious detections. Combining the results of both configurations provides a global dataset of ground-based GW measurements, which enables the calculation of GW parameters. These can be used for improving NWP models.

Global‐ and Local‐Scale High‐Resolution Event Catalogs for Algorithm Testing

ABSTRACTDuring the development of new seismic data processing methods, the verification of potential events and associated signals can present a nontrivial obstacle to the assessment of algorithm performance, especially as detection thresholds are lowered, resulting in the inclusion of significantly more anthropogenic signals. Here, we present two 14 day seismic event catalogs, a local‐scale catalog developed using data from the University of Utah Seismograph Stations network, and a global‐scale catalog developed using data from the International Monitoring System. Each catalog was built manually to comprehensively identify events from all sources that were locatable using phase arrival timing and directional information from seismic network stations, resulting in significant increases compared to existing catalogs. The new catalogs additionally contain challenging event sequences (prolific aftershocks and small events at the detection and location threshold) and novel event types and sources (e.g., infrasound only events and long‐wall mining events) that make them useful for algorithm testing and development, as well as valuable for the unique tectonic and anthropogenic event sequences they contain.

CIVIL AND SCIENTIFIC APPLICATION OF IMS NETWORK DATA IN EARTHQUAKE HAZARD ASSESSMENT

International Monitoring System (IMS), using four technologies – seismic, hydroacoustic, infrasound and radionuclide. While awaiting entry-into-force, the IMS is operating in test mode yet, even now, monitoring data have potential use among the scientist for the social welfare means. Contribution to the earthquake hazard and related earthquake engineering determinations is a big development and knowledge expansion of the one of the cited technology i.e. seismic. In this direction Indonesian region bounded by 14°S–10°N and 93–141°E, which is one of the most seismically Trans-Asian and Circum-Pacific belts type active plate regions of the world where large to great earthquakes have occurred during the past hundred years have been considered. Nineteen years recent earthquake data from June 13, 1999 to July 10, 2017 have been taken from International Monitoring System (IMS) Network setup by Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), Vienna Austria. These data analyses shows that earthquake occurrences agrees with the Gumbel’s Type I extreme distribution function and has been applied to analyses those maximum magnitude data with a satisfactory degree of correlation (0.96). The earthquake hazard that existed in Indonesian region been quantified in terms of recurrence periods and probabilities of occurrence of earthquake of any given magnitude. This investigation indicates that the most probable largest annual earthquakes are close to 6.0. Also, most probable earthquake that may occur in an interval of 50 years is estimated as 6.8. Other medium to large size earthquakes which are expected to occur in this region has been predicted that may help in engineering investigations at particular site and decision making problems if planning to develop certain region for infrastructural activities.

CONTRIBUTION OF KAZAKHSTAN STATIONS OF THE INTERNATIONAL SYSTEM INTO GLOBAL AND REGIONAL MONITORING

The contribution of Kazakhstani stations has been suumarized in comparison with other stations of the International Monitoring System (IMS) in a number of associated phases into the REB bulletin (Reveiwed Events Bulletin) of the International Data Center (IDC). It has been demostrated that all stations of Kazakhstan, both seismic and infrasound ones, are quite effective in monitoring and take one of the first places. This is confirmed by the results of mapping of the epicenters of the events of the world as well as such parameters as minimum amplitude and proportion of a number of events detected with participation of Kazakhstani stations to the general number of events in REB. The region of Central Asia (CA) has been considered in detail in the REB results as well as bulletins of Kazakhstan National Data Center (KNDC) – seismic and infrasound – with examples of estimate of real-time accuracy of locations. Infrasound bulletin of events of KNDC on CA has been compared with REB. In KNDC bulletin the location has been implemented as per data of four infrasound stations, including one Russian station Zalesovo. A larger number of events has been noted in KNDC bulletin in comparison with the REB one.

The Comprehensive Nuclear-Test-Ban Treaty (CTBT): seismic monitoring

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is briefly characterized as a global arms control and disarmament initiative, which complements the goal of the Non-Proliferation Treaty (NPT). The verification regime of the CTBT is designed to monitor countries’ compliance with the CTBT by detecting any nuclear explosion conducted on Earth - underground, underwater or in the atmosphere. This paper briefly goes through the International Monitoring System (IMS) of CTBT’s verification regime that uses four different technologies - seismic, hydroacoustic, infrasound and radionuclide - to monitor the planet for nuclear explosions. It pays particular attention to the seismology monitoring techniques of CTBT IMS, including the practical steps in discriminating underground explosions and earthquakes using data mainly from the IMS seismic network. It also highlights the seismic analyses performed by the Malaysian CTBT National Data Centre (MY-NDC) that in principle, applies the practical steps of CTBT nuclear explosion seismology monitoring. In summary underground explosions produced seismic waves with unique characteristics which allowed the discrimination between explosions and earthquakes.

Modelling ocean ambient noise with finite ocean depth and comparisons with observations

The global International Monitoring System (IMS) network continuously detects coherent ambient infrasound noise between 0.1 and 0.5 Hz. This noise, referred to as microbaroms, is generated by the second order non-linear interaction of ocean waves, mostly during severe storms. A global and multi-year analyze of microbaroms highlights the strong influence of middle atmospheric conditions on the propagation. Various source models have been developed. Brekhovskikh et al. (1973) and Ardhuin and Herbers (2013) considered a source directivity effect in infinite depth ocean with radiative pressure depending on the wave elevation angle. Waxler and Gilbert (2006) and Waxler (2007) investigated the radiation of infrasound by ocean waves in finite depth ocean by monopolar sources. In this study, the combined effects of non-monopolar source and bathymetry on the radiation are addressed. Beyond theoretical issues, source modelisation and propagation through a realistic atmosphere are carried out. Comparing the predicted signals with the observed ones at all IMS stations shows good agreements for both directional and amplitude information. Building a global reference database of oceanic noise sources opens new perspectives for providing additional integrated constraints on middle atmosphere dynamics and disturbances.The global International Monitoring System (IMS) network continuously detects coherent ambient infrasound noise between 0.1 and 0.5 Hz. This noise, referred to as microbaroms, is generated by the second order non-linear interaction of ocean waves, mostly during severe storms. A global and multi-year analyze of microbaroms highlights the strong influence of middle atmospheric conditions on the propagation. Various source models have been developed. Brekhovskikh et al. (1973) and Ardhuin and Herbers (2013) considered a source directivity effect in infinite depth ocean with radiative pressure depending on the wave elevation angle. Waxler and Gilbert (2006) and Waxler (2007) investigated the radiation of infrasound by ocean waves in finite depth ocean by monopolar sources. In this study, the combined effects of non-monopolar source and bathymetry on the radiation are addressed. Beyond theoretical issues, source modelisation and propagation through a realistic atmosphere are carried out. Comparing the predicte...

Improved infrasound array processing with robust estimators

Accurate infrasound source and path characterization rely on high-quality array processing parameter estimates. Physical and statistical assumptions underlying conventional array processing techniques sometimes fail in practice due to propagation effects or station degradation. Unlike conventional least squares regression, robust regression estimators are relatively insensitive to data that deviate from the assumed planar model. We compare two such estimators, M-estimators, and least-trimmed squares (LTS), to conventional array processing methods (frequency-wavenumber beamforming, progressive multi-channel cross correlation, L1 regression, and ordinary least squares) using synthetic and real infrasound data. Synthetic testing suggests that robust estimators are resistant to timing errors and noise contamination. We also present case studies from both International Monitoring System and the Alaska Volcano Observatory infrasound data that demonstrate how these techniques have produced accurate array processing results despite an element polarity reversal, timing error due to the loss of GPS lock, and a deviation from the plane wave assumption. We also evaluate the effectiveness of these techniques to arrays with differing geometries and number of elements, and note that the examination of LTS residuals enables outlying inter-element differential times to be flagged automatically, providing a data quality tool.

A multi-technology analysis of the 2017 North Korean nuclear test

Abstract. On 3 September 2017 official channels of the Democratic People's Republic of Korea announced the successful test of a thermonuclear device. Only seconds to minutes after the alleged nuclear explosion at the Punggye-ri nuclear test site in the mountainous region in the country's northeast at 03:30:02 (UTC), hundreds of seismic stations distributed all around the globe picked up strong and distinct signals associated with an explosion. Different seismological agencies reported body wave magnitudes of well above 6.0, consequently estimating the explosive yield of the device on the order of hundreds of kT TNT equivalent. The 2017 event can therefore be assessed as being multiple times larger in energy than the two preceding North Korean events in January and September 2016. This study provides a multi-technology analysis of the 2017 North Korean event and its aftermath using a wide array of geophysical methods. Seismological investigations locate the event within the test site at a depth of approximately 0.6 km below the surface. The radiation and generation of P- and S-wave energy in the source region are significantly influenced by the topography of the Mt. Mantap massif. Inversions for the full moment tensor of the main event reveal a dominant isotropic component accompanied by significant amounts of double couple and compensated linear vector dipole terms, confirming the explosive character of the event. The analysis of the source mechanism of an aftershock that occurred around 8 min after the test in the direct vicinity suggest a cavity collapse. Measurements at seismic stations of the International Monitoring System result in a body wave magnitude of 6.2, which translates to an yield estimate of around 400 kT TNT equivalent. The explosive yield is possibly overestimated, since topography and depth phases both tend to enhance the peak amplitudes of teleseismic P waves. Interferometric synthetic aperture radar analysis using data from the ALOS-2 satellite reveal strong surface deformations in the epicenter region. Additional multispectral optical data from the Pleiades satellite show clear landslide activity at the test site. The strong surface deformations generated large acoustic pressure peaks, which were observed as infrasound signals with distinctive waveforms even at distances of 401 km. In the aftermath of the 2017 event, atmospheric traces of the fission product 133Xe were detected at various locations in the wider region. While for 133Xe measurements in September 2017, the Punggye-ri test site is disfavored as a source by means of atmospheric transport modeling, detections in October 2017 at the International Monitoring System station RN58 in Russia indicate a potential delayed leakage of 133Xe at the test site from the 2017 North Korean nuclear test.

Developing a drought-monitoring index for the contiguous US using SMAP

Abstract. Since April 2015, NASA's Soil Moisture Active Passive (SMAP) mission has monitored near-surface soil moisture, mapping the globe (between 85.044∘ N/S) using an L-band (1.4 GHz) microwave radiometer in 2–3 days depending on location. Of particular interest to SMAP-based agricultural applications is a monitoring product that assesses the SMAP near-surface soil moisture in terms of probability percentiles for dry and wet conditions. However, the short SMAP record length poses a statistical challenge for meaningful assessment of its indices. This study presents initial insights about using SMAP for monitoring drought and pluvial regions with a first application over the contiguous United States (CONUS). SMAP soil moisture data from April 2015 to December 2017 at both near-surface (5 cm) SPL3SMP, or Level 3, at ∼36 km resolution, and root-zone SPL4SMAU, or Level 4, at ∼9 km resolution, were fitted to beta distributions and were used to construct probability distributions for warm (May–October) and cold (November–April) seasons. To assess the data adequacy and have confidence in using short-term SMAP for a drought index estimate, we analyzed individual grids by defining two filters and a combination of them, which could separate the 5815 grids covering CONUS into passed and failed grids. The two filters were (1) the Kolmogorov–Smirnov (KS) test for beta-fitted long-term and the short-term variable infiltration capacity (VIC) land surface model (LSM) with 95 % confidence and (2) good correlation (≥0.4) between beta-fitted VIC and beta-fitted SPL3SMP. To evaluate which filter is the best, we defined a mean distance (MD) metric, assuming a VIC index at 36 km resolution as the ground truth. For both warm and cold seasons, the union of the filters – which also gives the best coverage of the grids throughout CONUS – was chosen to be the most reliable filter. We visually compared our SMAP-based drought index maps with metrics such as the U.S. Drought Monitor (from D0–D4), 1-month Standard Precipitation Index (SPI) and near-surface VIC from Princeton University. The root-zone drought index maps were shown to be similar to those produced by the root-zone VIC, 3-month SPI, and the Gravity Recovery and Climate Experiment (GRACE). This study is a step forward towards building a national and international soil moisture monitoring system without which quantitative measures of drought and pluvial conditions will remain difficult to judge.

SEISMICKÉ JEVY REGISTROVANÉ STANICÍ VRAC V ROCE 2017

Broadband seismic station VRAC, operated by Institute of Physics of the Earth (Masaryk University) and situated westwards of village Vranov u Brna, is equipped with seismometer STS-2 high gain and by digitizer Quanterra Q330. This instrumentation allows recording of broad band of frequencies from tenths of Hz to hundreds of seconds. It is important for usage of the VRAC station, which is part of several seismic networks, including Czech regional seismic network and global International Monitoring System of the CTBTO. In frame of these networks, station VRAC has to record of seismic signal of both local and teleseismic events. During year 2017, station VRAC recorded 6 855 seismic events (10 699 picked seismic phases). More than 70% of recorded events were represented by local events with epicentral distance less than 360 km. Induced events (mining tremors) and quarry blasts dominated among these local events. In addition, 197 natural tectonic events were recorded (89 on the territory of the Czech Republic). In the region of the Bohemian massif, most important natural seismicity was observed in the area of west Bohemia, where seismic swarm occured in July 2017. Exceptional tectonic event (10. 12. 2017, ML = 3.5) was recorded from the NE part of the Bohemian Massif (near Hlučín). About 25% of events registered by station VRAC were represented by teleseismic events with epicentral distance exceeding 2 000 km, including Korean nuclear test from 3. 9. 2017. Records of relatively small teleseismic events show signifi cant eff ect of the PKP caustic zone in respect of detectability of station VRAC.

Enhanced detection and estimation of regional S-phases using the 3-component ARCES array

In September 2014, the ARCES array in Northern Norway was upgraded to consist of 3-component instruments at each of its 25 sites. It is thereby the first array station of the International Monitoring System to be fully 3-component. S-phases are of paramount importance for the detection and location of seismic events at regional distances, especially given sparse station coverage, and it is important that these phases are both detected confidently and attributed accurate slowness estimates. The slowness estimates both identify the phase and provide phase association algorithms with the information necessary to form a high-quality seismic event hypothesis. Prior to September 2014, ARCES had 3-component sensors at four sites only. While these 3-component seismometers were highly beneficial for the detection of regional S-phases, often using incoherent beams, it was often more reliable to perform f-k analysis on the 25 vertical sensors rather than the small number of available horizontal waveforms. In addition to providing an increased signal-to-noise ratio, signals on the horizontal traces are more coherent for the S-phases and display a high measure of semblance over the array. This improves the stability of f-k analysis, since the estimates are less susceptible to the effects of scattering and incoherence. The improved coherence of S-phases across the array aperture on the horizontal components provides the basis for superior secondary phase detection capability using F-detectors and other coherence-based algorithms. Analysis of regional signal coda on the 3-component array indicates different characteristics of the apparent slowness on the different components. The 27 January 2018 earthquake on Novaya Zemlya was the first seismic event close to the former Soviet nuclear test-site to be recorded using the upgraded 3-component ARCES array. We examine the evolution of the slowness pattern for on the different components of the wavetrain and speculate that a continuous f-k detector on three components may be able to detect small seismic events in the eastern Barents Sea with increased robustness and sensitivity. We review the development of the instrumentation at ARCES and explain the motivation behind the hybrid response sensors currently deployed.

A radioxenon detection system using PIPS and CZT

This paper introduces and describes the initial characterizations of a prototype beta-gamma coincidence detection system that utilizes a PIPSBox and two coplanar CdZnTe detectors for atmospheric radioxenon identification and nuclear test ban treaty verification. Coincidences between four independent detecting bodies are identified in real time via a custom coincidence module implemented in a field-programmable gate array. The system is compact, maintains simple readout electronics, and provides high resolution radiation detection at room temperature operation. Preliminary measurements using 137Cs and 131mXe were conducted to optimize various system parameters to achieve optimal energy resolution of key spectral features. The purpose of this research was to explore the utility of these materials and methods for radioxenon monitoring in the International Monitoring System.

Assessing middle atmosphere weather models using infrasound detections from microbaroms

SUMMARYThe nonlinear interaction of ocean surface waves produces coherent infrasound noise—microbaroms—between 0.1 and 0.5 Hz. Microbaroms propagate through the atmosphere over thousands of kilometres due to low absorption and efficient ducting between the ground and the stratopause. These signals are globally and permanently detected by the International Monitoring System (IMS) infrasound network, which has been established to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty. At the International Data Centre (IDC) in Vienna, where IMS data are routinely processed, microbarom detections appear in overlapping frequency bands, and are treated as false alarms. Therefore, understanding the variability in microbarom detections is essential to support the IDC in the reduction of the false alarm rate. In this study, microbarom amplitudes and the direction of arrivals at the German infrasound station IS26 were modelled. For the simulations, the source was described by an operational ocean wave interaction model, and the signal amplitude was modelled using a semi-empirical attenuation relation. This relation strongly depends on middle atmosphere (MA; i.e. 15–90 km altitude) dynamics; however, vertical temperature and wind profiles, provided by numerical weather prediction (NWP) models, exhibit significant biases and differences when compared with high-resolution light detection and ranging instrument (lidar) soundings in altitudes where infrasound signals propagate. To estimate uncertainties in the modelled amplitude, a fully autonomous lidar for MA temperature measurements was installed at IS26. Temperature and wind perturbations, considering observed biases and deviations, were added to the operational high-resolution atmospheric model analysis produced by the European Centre for Medium-Range Weather Forecasts. Such uncertainties in horizontal winds and temperature strongly impact propagation conditions, explaining almost 97 per cent of the actual detections, compared to 77 per cent when using the direct output of the NWP model only. Incorporating realistic wind and temperature uncertainties in NWP models can thus significantly improve the understanding of microbarom detections as well as the detection capability of a single station throughout the year.

Listening and facilitating all forms of communication: disabled children and young people in residential care in England

ABSTRACTLittle research has been undertaken into how children with complex communication needs living in residential care are encouraged to express their views, be involved in decision-making, and importantly, make it known when they are unhappy. This group are often placed a long distance from home and can be some of the most vulnerable children in the care system. Ensuring they have access to a communication method, people who understand their communication and support to empower them to grow their capacity is not only a right and a safeguarding mechanism, it is also important in preparation for adulthood and for leaving care. This unique paper reports on the English arm of a European project, which aimed to devise the first international monitoring system to prevent abuse of disabled children in residential settings. Trained professionals examined how disabled children were heard, and encouraged to be involved in decision-making within 10 case-study residential settings. To aid international development of good practice, this paper focuses on positive aspects of practice. Examples are used to illustrate how all forms of communication can be encouraged and used positively to both protect and empower disabled children in residential care. Implications for practice are presented to support practitioners to create positive communication environments.

Characterization of GNSS Signals Tracked by the iGMAS Network Considering Recent BDS-3 Satellites

The international GNSS monitoring and assessment system (iGMAS) tracking network has been established by China to track multi-GNSS satellites. A key feature of iGMAS stations is the capability to fully track new navigation signals from the recently deployed BDS-3 satellites. In addition to the B1I and B3I signals inherited from BDS-2 satellites, the BDS-3 satellites are capable of transmitting new open service signals, including B1C at 1575.42 MHz, B2a at 1176.45 MHz, and B2b at 1207.14 MHz. In this contribution, we present a comprehensive analysis and characterization of GNSS signals tracked by different receivers and antennas equipped in the iGMAS network, especially as they relate to BDS-3 signals. Signal characteristics are analyzed in terms of the carrier-to-noise density ratio for the different signals as measured by the receiver, as well as pseudo-range noise and multipath. Special attention is given to discussion of the satellite-induced code bias, which has been identified to exist in the code observations of BDS-2, and the inter-frequency clock bias (IFCB), which has been observed in the triple-frequency carrier phase combinations of GPS Block IIF and BDS-2 satellites. The results indicate that the satellite-induced code bias is negligible for all signals of BDS-3 satellites, while small IFCB variations with peak amplitudes of about 1 cm can be recognized in BDS-3 triple-carrier combinations.