Research Required to Support Comprehensive Nuclear Test Ban Treaty Monitoring (1997) / Chapter Skim
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3 Monitoring Technologies: Research Priorities
3 Monitoring Technologies: Research Priorities
Pages 49-82
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From page 49... ...
monitoring efforts will focus on certain areas of the world, those areas are still extensive. In many cases, the locations lack prior nuclear testing for direct calibration of identification; they require calibration efforts to improve location capability; and, for the most part, they have not been well instrumented seismologically.
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From page 50... ...
One of the core philosophical issues for seismic monitoring operations is whether it is better to use global and/or regional travel time curves, possibly with station or source region corrections, or to explicitly use models of the Earth's velocity structure and calculate the travel times and amplitudes for each source-station pair. The velocity models, which can include variable crustal and lithospheric structure, can be derived from the same data used in defining local travel time curves, but once they are determined they could also be used to model additional seismic signals that are not employed in standard event processing, such as free oscillations, surface waves, and multiple-body ~9 The moment tensor is a representation of the set of equivalent forces at the source that would produce the observed ground motion.
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From page 51... ...
Velocity models also have a key advantage completely lacking in travel time curves: they provide the basis for synthesizing the seismic motions expected for a specific path, as involved in the regional wave modeling mentioned above. The synthetic ground motions are useful for estimates of improving the source depth, identifying blockage of certain phase types, and enhancing the identification of Me source type.
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52 55 45 4C 35 30 RESEAR CH REQ WIRED TO S UPPOR T CTB T MONI TONING Velocity at 100 km depth add...
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53 of of of of of of A A 9° ~A Of FIGURE 3.2 Detection threshold predicted for the fully deployed IMS Primary Network. The station locations are indicated as black squares on the map.
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, but these typically do not account for possible systematic error and hence may overestimate event location accuracy. Figure 3.3 presents a
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0 ~0 ~0 ~0~ 55 FIGURE 3.3 Estimates of location precision for the IMS Primary and Auxiliary networks for (a) magnitude 4.25 events and (b)
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From page 56... ...
Such uncertainty also serves as motivation for further development of velocity models because the many data sources that can be incorporated into such models can resolve heterogeneities that are not calibrated directly by ground truth events. A major basic and applied research effort of great importance for event location capabilities involves developing regionalized travel time curves and velocity models, particularly for the crustal phases that will be detected for small events.
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From page 57... ...
causes the energy partitioning to change among phases; for example, some crustal paths do not allow the Lg phase to propagate, and anomalously large Sn phases may be observed instead. Waveform modeling approaches can play a major role in determining the local velocity structures required to interpret regional phases for both event location and event identification, so there is value in further development of seismological modeling techniques that can compute synthetic ground motions for complex models.
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From page 58... ...
In addition to station corrections, which account for systematic station-dependent biases, it is important to determine regionalized amplitudedistance curves analogous to regional travel time curves. These curves are used in the magnitude formulations and have great variations at regional distances (see Appendix D)
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From page 59... ...
. Summary of Research Priorities Associated with Seismic Monitoring In summary, a prioritized list of research topics in seismology that would enhance CTBT monitoring capabilities includes: 1)
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For example, calculations show that an atmospheric explosion of 1 kt at a height 1 km above the surface will couple energy RESEARCHREQUIRED TO SUPPORT CTBT MONITORING into the SOFAR channel roughly equivalent to the detonation of a 10-50 kg explosion at channel depth, which is five orders of magnitude less than 1 kt. Sound pressure level scaling (which is proportional to pressure squared)
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From page 62... ...
At present, for example, the hydroacoustic monitoring com RESEARCHREQUIRED TO SUPPORT CTBT MONITORING munity refers all signal levels to 1 microvolt at the receiving hydrophore. The rest of the hydroacoustic community refers signal levels to a pressure level of 1 pPa at 1 m.
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From page 63... ...
Only through the development of robust automatic detection and noise rejection algorithms, coupled with synergy with other monitoring technologies, can the proposed IMS hydroacoustic system be useful. Association and Location The hydroacoustic network will rely on the association of arrivals from at least three different stations to perform cross-fixing and location of the event.
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From page 64... ...
Finally, although hydroacoustic and T-phase stations cover a fairly large portion of the world where seismic stations are sparse, their ultimate performance must be understood in the context of the larger system, and the improvements to be realized by the addition of infrasonic and seismic information must be evaluated. Summary of Research Priorities Associated with Hydroacoustic Monitoring In summary, a prioritized list of research topics in hydroacoustics that would enhance CTBT monitoring capabilities includes: 1)
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From page 65... ...
However, extensive experience gained in the 1950s and 1960s indicates that infrasonic monitoring may prove to have relatively few operational limitations for CTBT monitoring. Appendix F provides background and further perspectives of technical issues in this area.
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From page 66... ...
are pressure fluctuations in the turbulent atmospheric boundary layer and the background of infrasound arising from geophysical sources. With the exceptions of quarry blasts, other chemical explosions, and missile launches, relatively few human processes produce sounds that could mask nuclear explosions.
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Their acoustic signatures contain higherfrequency components that can distinguish them from underground nuclear explosions. · Severe weather.
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Further research on the application of data-adaptive, frequency domain filters to infrasonic data should be pursued to enhance the detection of low level CTBT monitoring station .
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Propagation models should include the range dependence of atmospheric variables. Additional analyses of past infrasound data on nuclear explosions as a function of yield and path would be useful.
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. Summary of Research Priorities Associated with Infrasound Monitoring In summary, a prioritized list of research topics in infrasonics that would enhance CTBT monitoring capabilities includes: 1 )
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RESEARCH REQUIRED TO SUPPORT CTBT MONITORING release under conditions of low pressure and reduced or no release under high-pressure conditions. The present plan for remote CTBT radionuclide monitoring is to install a series of fixed stations around the world that have fully automated measurement devices with the ability to collect, process, and send the results to a central station on a daily basis.
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From page 73... ...
Rapid noble gas monitoring equipment mounted in slowmoving aircraft to perform the initial screening of an area may identify the approximate test location; however, the escaping gas may not be present in sufficient amounts to allow detection. Such aerial surveys may require the collection and rapid analysis of many air samples over a wide area.
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From page 74... ...
Because of the low air sampling rates of current noble gas monitors compared to particulate monitors, CTBT noble gas monitoring is considered to be about 1000 times less sensitive than particulate monitoring, and there have been questions about how extensively such monitors should be employed in the proposed worldwide network (Ad Hoc Committee on a Nuclear Test Ban, 1995~. The prototype technology being developed by Battelle (Pacific Northwest National Laboratory tPNNL]
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From page 75... ...
The IMS system is focused on a worldwide network of fixed stations, all of which will monitor radioactive particulates and some of which will monitor radioactive noble gases. Although the response from a fixed station seismic, hydroacoustic, and infrasonic monitoring network will be rapid, the response of the fixed station radionuclide monitoring network will be relatively slow.
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From page 76... ...
The primary motivation for these projects is to enhance the capability to monitor radioactive materials from nuclear explosions and nuclear reactors that have been dumped in the ocean. These systems will involve sampling by aircraft, remote underwater stations, and buoys.
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From page 77... ...
Samples would be particulate filter papers collected from field systems such as DOE particulate samplers or from the proposed rapid response teams. Rapid collection and analysis of these samples is again required because of the short halflives of some products such as 97Zr (17 hours)
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From page 78... ...
There is also a need to develop infrastructure for rapid airborne and waterborne monitoring of noble gases and particulates and to develop a rugged system for gas sampling during On-Site-Inspections. While the panel notes that these are primarily systems development and implementation tasks, they facilitate many of the above radionuclide monitoring problems.
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From page 79... ...
For example, explosions and earthquakes on land can generate hydroacoustic 79 waves at continental margins, and upcoming seismic waves that strike the ocean floor can generate pressure waves in the water that are detectable by hydroacoustic sensors. Similarly, the surface motion from a shallow explosion on land or in the oceans can generate pressure pulses in the air that may be detected by infrasonic sensors.
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From page 80... ...
For example, the development of ground truth data bases for each monitoring method could be augmented by coordinated use of overhead imagery. This has been established in the past for major nuclear test sites, where surface collapse craters could be associated with seismic event locations to calibrate the seismic array, eliminating biases due to unknown Earth structure.
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From page 81... ...
Summary of Research Priorities Associated with Synergy In summary, a prioritized list of research topics to increase the synergy between CTBT monitoring technologies includes: 1) Improved understanding of the coupling bet~veen hydroacoustic signals and ocean islandrecorded T-phases, with particular application to event location in oceanic environments.
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From page 82... ...
Its value could be enhanced if it were possible to RESEARCH REQUIRED TO SUPPORT CTBT MONITORING attribute the nuclear device to a limited number of sources on the basis of chemical and physical properties of materials in the debris another area of potentially fruitful research.
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