Research Required to Support Comprehensive Nuclear Test Ban Treaty Monitoring (1997)

The physical processes associated with nuclear explosions produce distinctive sources of acoustic waves, elastic waves, radiation, and radioactive materials and gases. These signals and products then propagate through or are advected by the Earth system with various transmission effects, and may eventually be detected by different types of sensors placed around the planet's surface or on satellites. The types of signals that can be recorded and interpreted are limited by the extensive background noise of the Earth (e.g., earthquakes, weather phenomena, conventional explosions), and the physical limitations of the sensors (e.g., bandwidth, sensitivity). Signals recorded at different locations must be retrieved from the field, associated with a time and location for a common source using general knowledge of signal propagation. Attributes of the recorded signals, corrected for propagation and instrumentation effects, are then used to identify the type of source, ideally distinguishing nuclear explosion signals from earthquakes or other non-nuclear phenomena. All monitoring technologies share these fundamental elements; source excitation, signal propagation or advection, recording instrumentation, event association, event location, and event identification. They also share the technological challenges of data retrieval and automation of data analysis.

Any CTBT monitoring system will have practical limits in the capabilities to detect, locate, and identify events based on the analysis of the recorded signals. These limits are imposed both by cost considerations that constrain the data acquisition and processing and by intrinsic constraints of the monitoring technologies. A complete interpretation of the monitoring limits must allow for the possibility of various evasion approaches, such as muffling the nuclear explosion signals by detonation of the device in a pre-existing cavity (decoupling) or obscuring the explosion signal by simultaneous detonation with an earthquake, quarry blast, or mine collapse. More than 50 years of research underlies the present ability to use the various wave types in diverse environments for monitoring applications. The significant progress that has been achieved has provided the technical basis for moving forward with the CTBT negotiations. However, the national objectives for assuring international compliance with a total ban on nuclear explosions place extreme demands on all of the monitoring technologies and operational systems, and there is a need for continuing research to enhance the entire U.S. CTBT monitoring system.

It is clear from the CTBT negotiating record that a monitoring capability of ''a few kilotons, evasively tested" in selected areas of the world is the goal for U.S. monitoring capabilities.²⁴ The primary technical challenge associated with the CTBT is related to the fact that even very small tests are banned. In this setting, decreasing the magnitude threshold for the monitoring goals has several important implications for the performance of a monitoring system: the overall number of detected events increases sharply, the number of stations in a fixed network capable of detecting a given event decreases, and the distance at which detections can be made decreases. Given these factors, the detection, location and identification of small events by the combined IMS and NTM assets involves the analysis of signals recorded at regional distances where signal propagation is often complicated and regionally varying. Even with only a few reporting stations, a monitoring system needs to provide high confidence locations with an uncertainty smaller than 1000 km² for on land events. This requirement reflects operational requirements mandated by the On-Site Inspection provisions of the treaty (Protocol to the CTBT, Part IIA). Given these requirements, the challenge of precisely locating and confidently identifying all small events at some low magnitude threshold given sparse monitoring networks is formidable. Meeting it requires a sustained basic research program in support of CTBT monitoring.

Political realities mandate a long-term commitment by the U.S. government to monitor international compliance with the CTBT, using cost-effective, highly reliable technologies. Present technologies cannot achieve the highest levels of confidence at very low yields, and this prompted President Clinton to call for "pursuing of a comprehensive research and development program to improve our treaty monitoring capabilities and operations" as one of six CTBT Safeguards. Thus, a sustained basic research program is required to enhance the performance of the U.S. CTBT monitoring system. This report identifies key areas of research that will contribute to achieving the national monitoring goals: the disciplines of seismology, hydroacoustics, infrasonics, and radionuclides, all elements of the U.S. National Data Center and the International Monitoring System

The research program that will best serve the national needs will sustain both long-term and short-term efforts, and will span the spectrum from innovative exploratory research to advanced development efforts. It will draw upon expertise in universities, private industry, and U.S. National Laboratories. The external research program supporting non-governmental fundamental research should involve a funding level in excess of the current commitment ($8.8M). This is in addition to the internal programs of DOE and DoD and the developmental research that supports the IDC and NTM. There should be close coordination between DoD and DOE elements of this program, and strong integration with the operational effort conducted by the U.S. National Data Center operated by the Air Force Technical Applications Center, on-going interactions with the policy community, and cooperation with agencies using similar technologies to address challenges of national interest. The panel emphasizes that open access to IMS data would facilitate this cooperation that would be of great benefit to CTBT monitoring.

The panel elaborates on these issues in response to the elements of its charge.

What are the basic research problems remaining in the fields of seismology, hydroacoustics, infrasonics and radionuclides that should be pursued to meet national and international requirements for nuclear monitoring? The panel's work on this question should anticipate quality of data to be made available in the future, in particular those data from the CTBT International Monitoring System.

The United States has 5 primary technical CTBT monitoring methodologies available to it: seismology, hydroacoustics, infrasound, radionuclide, and satellite systems. All have mature theoretical development, advanced recording instrumentation,

and efficient data collection, but they differ significantly in the specific technical challenges that arise for CTBT monitoring and the amount of prior global monitoring experience that is available for them. The first four of these form the basis of the IMS capabilities. Recommended research areas for these disciplines are described below.

Seismological monitoring is an advanced and mature discipline in many areas related to CTBT monitoring. For decades, nuclear testing treaties have been verified using seismic monitoring of teleseismic signals (i.e., signals that are recorded at distances larger than 2000 km from the source). These signals have relatively simple propagation effects that are now well understood. Using such data, global detection, location, and identification of all underground events above magnitude 4.5 appears to be straightforward given an adequate distribution of recording facilities. As now planned, IMS and NTM assets will meet this requirement.

Teleseismic signals are weak, however, for the small events of interest for CTBT monitoring (including events with magnitudes as low as 2.0 in some regions). Consequently, treaty verification will necessitate increased dependence on regional signals of small events, observed at distances less than about 1000 km. These signals are complicated by reverberations in the crust, but they often have good signal-to-noise ratios.

Pushing the seismic monitoring magnitude threshold downward to include precise event location and high confidence identification for small events is the primary motivation for continued seismological research. For this reason, there is need for research on all aspects of detecting, locating and identifying events in the magnitude range 2.0–4.5 using regional signals from known sources in diverse regions of the world. For this task, the IMS and NTM seismic stations need to be carefully calibrated for location and magnitude determinations using regional distance observations in various parts of the world. The many other seismic stations that exist outside of the NTM and IMS systems can be used to determine crustal properties, ground-truth event parameters, and development of innovative analysis procedures. In addition, research on the characteristics of seismic radiation from small events and seismic wave propagation in the heterogeneous crust of the Earth should be conducted. This will improve the capability to identify small nuclear explosions amidst a background of numerous small earthquakes and quarry blasts. A prioritized list of research activities in support of seismic monitoring includes:

1. Improved characterization and modeling of regional seismic wave propagation in diverse regions of the world.

2. Improved capabilities to detect, locate, and identify small events using sparsely distributed seismic arrays.

3. Theoretical and observational investigations of the full range of seismic sources.

4. Development of high-resolution velocity models for regions of monitoring concern.

Monitoring sound waves in the oceans is a well-advanced discipline, primarily as a result of investments in Anti-Submarine warfare. The ocean medium is a remarkably efficient transmitter of low frequency acoustic waves, so that even modest conventional explosions in most regions of the deep oceans are readily detected and identified with adequate instrumentation. Because hydroacoustic waves also couple efficiently into seismic waves at the ocean bottom (and vice versa), the medium can be effectively monitored by a combination of hydroacoustic and seismic networks.

To date, there has been relatively little research on the use of hydroacoustic signals to monitor underground and atmospheric explosions. Given that the proposed IMS hydroacoustic network will use a small number of sensors, with no directional capabilities, the panel concludes that the system will have extremely limited detection and location capabilities. Using only hydroacoustic data, it will be difficult to reduce false alarms from natural and human sources and to identify and locate sources in shallow or polar regions. Because of these deficiencies, there is a need for research on synthesizing hydroacoustic data with seismic, infrasonic, and radionuclide information and to assess the capability of the integrated system to monitor

within national goals. Prioritized research topics in support of hydroacoustic monitoring include:

1. Improvements in source excitation theory for diverse ocean environments, particularly for earthquakes and for acoustic sources in shallow coastal waters and low altitude environments.

2. Understanding the regional variability of hydroacoustic wave propagation in oceans and coastal waters and the capability of the IMS hydroacoustic system to detect these signals.

3. Improved characterization of the acoustic background in diverse ocean environments.

4. Improving the ability to use the sparse IMS network for event detection, location, and identification and developing algorithms for automated operation.

While several atmospheric nuclear tests were conducted after negotiation of the Limited Test Ban Treaty in 1963 (by non-signing nuclear weapon states, China and France), the reduction of such tests relative to the prior two decades brought about a decrease in atmospheric sound wave monitoring efforts by the United States This trend will be reversed by the IMS system which will establish a global array of infrasound sensors to enable routine monitoring of low frequency sound waves on a global basis for the first time in decades. At present, however, the United States has only a few experts in infrasound, and virtually no infrastructure for research in atmospheric monitoring using sound waves. Thus, the primary research issues associated with CTBT monitoring involve first-order questions about the background noise, involving wind noise reduction and the nature and frequency of events such as volcanic explosions, meteor impacts, sounds radiated from ocean waves (microbaroms), auroral infrasonic waves, and mountain associated waves. Research on these questions would be augmented by publication of basic information on the U.S. monitoring experience in the 1950's and 1960's. This would enable a wider understanding of likely infrasound signal strength for explosions of different yield, different environments, and different distances from sensors. To support and enhance the monitoring capabilities of the IMS infrasound network, the following are priority research topics:

1. Characterizing the global infrasound background using the new IMS network data.

2. Enhancing the capability to locate events using infrasound data.

3. Improving the design of sensors and arrays to reduce noise.

4. Analyzing signals from historical monitoring efforts.

Radionuclides released from a nuclear explosion are distinct from nuclear reactor emissions and natural background radioactivity. Because radionuclide analysis can provide unambiguous evidence of a nuclear explosion, the IMS will receive data from a global network of fixed particulate and noble gas detectors. The data from this network will differ from the other monitoring technologies in two important respects. First, the raw data streams will consist of daily gamma-ray spectra for samples of wind transported gases and particulates, rather than the time series of seismic, hydroacoustic, and infrasound data. Consequently, there will be significant challenges in merging the analysis of radionuclide datasets with the other components of the IMS system. Second, and most important, the radionuclide network requires time scales as long as 10 days to two weeks to detect a possible nuclear explosion. This delay is sensitive to the rates of wind-borne transport of radionuclide particulates and the integration times for radiochemical analyses. Once an event is detected, further analyses of wind and climate patterns are required to back-track the data to locate the site of an explosion.

Given these limitations, a wide range of research is needed to strengthen the capabilities of radionuclide monitoring. Improvements are needed in the understanding of source terms.²⁵ and the airborne transmission effects. The source issues involve characterization of radioactive emissions from past nuclear tests (atmospheric, underwater,

and underground), with an emphasis on understanding atmospheric rain-out and underground absorption. Research is needed to study the various atmospheric effects associated with the dispersal of radioactive materials to improve the atmospheric transport models used for back-tracking of airborne radionuclides. In addition, there is a need to develop new instrumentation, infrastructure, and procedures for rapid radiochemical measurements. The goal of these efforts is to reduce the time delay between potential explosions and radionuclide detection, and to facilitate the work of On-Site Inspection teams. Priority research topics include:

1. Research to improve models for back-tracking and forecasting the air borne transport of radionuclide particulates and gases

2. Research and data survey to improve the understanding of source term data.²⁶

3. Understanding of atmospheric rain-out and underground absorption of radionuclides from nuclear explosions.

   Assessment of the detection capabilities of the IMS radionuclide network.

4. Research on rapid radiochemical analysis of filter papers.

5. Development of a high resolution, high efficiency gamma detector capable of stable ambient temperature monitoring.

What research is necessary to strengthen the synergy between the seismic, hydroacoustic, infrasonic, and radionuclide data sets to improve overall monitoring capability and to meet national and international requirements?

There are great opportunities to enhance the synergies between the different CTBT monitoring technologies. Energy propagating in the Earth system can couple from one medium to another (air to water, air to land, or land to water). Each monitoring technology has primary capabilities for sources in a particular medium as well as complementary roles for sources in the other media. For example, explosions and earthquakes on land can generate hydroacoustic signals when their seismic waves strike the continental boundaries or come up under the ocean bottom and convert to sound waves in the water. Possibilities for synergies in the use of diverse wavetypes exist in all stages of the monitoring process. Priority multi-disciplinary research that will enhance the synergy of monitoring technologies include:

1. Improved understanding of the coupling between hydroacoustic signals and ocean island-recorded T-phases, with particular application to event location in oceanic environments.

2. Integration of hydroacoustic, infrasound and seismic wave arrivals into association and location procedures.

3. Use of seismo-acoustic signals together with an absence of radionuclide signals for the identification of mining explosions.

4. Explore the synergy between infrasound, NTM, and radionuclide monitoring for detecting, locating, and identifying evasion attempts in broad ocean areas.

5. Determine the false alarm rate for each monitoring technology when operated alone and in conjunction with other technologies.

In addition, research synergy would be promoted by the communication of research advances and operational needs at annual multidisciplinary workshops.

How should the research results be transitioned so that they are most useful to those responsible for monitoring and verifying a CTBT?

Continuing basic research must be accompanied by effective mechanisms for transitioning research advances from academia and industry into the operational environment and for making the operational needs known to the research community. Given the continuing need for innovative exploratory research, advanced developmental research and operational advances, and realistic funding projections, the panel recommends that external research programs of DoD and DOE should be carefully coordinated so that a balance of basic and applied efforts can be sustained. It is important to buffer fundamental research efforts from short-term operational needs, otherwise creativity and innovation will be curbed. At the same time, it is important that the research community be aware of the potential applications of

their work. The CTBT research program should adopt a hierarchical research infrastructure consisting of a broadly-based basic research program, overlain by increasingly focused applied research efforts that develop and support the transition of promising technologies into the operational environment. Past administrative subdivisions of basic, applied and advanced developmental efforts have not worked efficiently in the Air Force test ban treaty monitoring program, in part due to fluctuations and uncertainties in the budgets of the separate efforts. The CTBT research program requires more effective oversight, coordination, and funding stability than have existed for the last decade.

The panel concludes that increased numbers of Ph.D. level research staff at the U.S. National Data Center would help to promote technology transfer to the operational regime. Technical training and sophistication is essential for recognizing and rapidly incorporating research advances into operational systems.

An additional means by which research efforts can be effectively transitioned to the operational environment would be the establishment of a CTBT research test bed. This would require a facility that replicates significant aspects of the IMS and U.S. NDC monitoring system, with real-time data processing capabilities and historical data archive access. The prototype-IDC has operated a limited system of this type, with visitors to the Center for Monitoring Research accessing the IMS data and processing system, but there is at present no clear plan for a broadly accessible test bed system for the long-term. Progress on many of the research issues raised in Chapter 3 will require researchers to analyze actual signals from the various monitoring disciplines, and have an opportunity to test proposed analysis methods. This would cultivate the development of new methods in a software environment that is much closer to the operational situation than currently exists at any university or private company, as well as providing realistic constraints on the processing. A test bed facility could also serve as a site for focused investigations of problem events in which technical experts gather to address technical issues (either in person or by computer link-ups). This could be designed to be responsive both to short-term and long-term problems that arise in the operational arena. Finally, such a test bed could form the basis for regularly scheduled exchanges between the policy and technical communities that would make clear the processes, constraints and uncertainties under which both communities operate. One possibility would be to have the prototype-IDC transition into this type of test bed facility once the permanent IDC is established in Vienna. This would require substantial funding beyond that described in the basic research budget above.

What are characteristics of a long-term program that would provide a stable, but adaptable base of support to those responsible for monitoring and verifying a CTBT?

The FY97 Department of Defense (DoD) external research program is presently funded at a level of $8.8M and DOE will provide about $0.4M ($4M/yr had been provided from FY95 and FY96 budgets) to external research out of the total FY97 DOE CTBT budget of $69.6M. The DoD FY97 budget for development of the IDC system is about $20M, which will need to be sustained at least until the IMS system is deployed.

If the United States is to meet stated national monitoring goals in a timely manner, increased funding (compared to the above budget levels) will be needed to support the high-priority research issues listed in Chapter 3. Pursuing the panel's recommendations on priority research will also require close coordination between several agencies. This effort will include focused missions to:

1. develop a new generation of Earth event catalogs in selected regions, listing all natural phenomena and human related sources down to magnitudes that are significantly below present-day capabilities;

2. utilize the data from the new global network of infrasound and radionuclide monitors;

3. improve global seismic velocity models;

4. integrate seismic and infrasound data to support the limited hydroacoustic network;

5. quantify the effect of seasonal variability on the location and detection capabilities of the hydroacoustic network; and

6. coordinate efforts to understand the structure of the crust and lithosphere in areas of interest to the United States at a level that allows reliable event identification.

The decision about whether to fund and pursue these research efforts will be influenced by assessments of the adequacy of CTBT verification and the benefits of these research undertakings.

To strengthen the CTBT research program it is also important to stabilize of the research budgets, with a multi-year commitment that firmly establishes the viability of this research area for intellectual resources in universities and private companies. This stability is essential for training technically competent scientists and researchers who will participate in U.S. monitoring operations and provide assessments of technical issues, problem events, and erroneous claims made by other nations. Without it, bright young researchers will not enter the fields supportive of CTBT monitoring. This research program should be buffered from fluctuations imposed by systems development and operational emphases, but should be run with effective communications of operational needs to the research community.

Research in the field of seismology is largely driven by the large numbers of non-nuclear events (earthquakes and conventional explosions) whose signals must be discriminated from those of potential nuclear explosions. Research challenges in the fields of hydroacoustics, infrasound and radionuclide monitoring will become more focused with the operation of the CTBT monitoring system. The panel notes that there is limited research support for some of the monitoring technologies outside of the CTBT research program, particularly for infrasonics and hydroacoustics. The rationale for increasing the current research program is that there are major unsolved problems in seismology, and that there will soon be a substantial flow of data from infrasound, radionuclide and hydroacoustic systems for which there is far less operational experience. Calibration of these systems involves both experimental and research issues, and support for university and contractor programs is vital to establishing a pool of national expertise in the analysis of these data, both for national CTBT monitoring activities and for competent assessment of claims that may be made by other countries based on observations from these technologies. At the same time, the balance of effort needs to reflect the role that these systems play in the overall U.S. capability, including satellite assets.

Additional conclusions regarding the stability and effectiveness of a CTBT research program include the following:

1. The 1996 consolidation of the DoD research program into a single program structure (now administered by the Defense Special Weapons Agency (DSWA) for the Nuclear Treaty Program Office (NTPO)), provides an unprecedented opportunity to form DoD's program into an effective CTBT research effort. This program should be structured to accommodate both long-term and short-term activities, as well as wide-ranging basic research and focused developmental research, if it is to prove effective in supporting the CTBT monitoring effort.

2. The panel concludes that the quality of research programs will be enhanced by the use of peer-review systems. Some applied, and most advanced developmental activities, can best be pursued with focused Requests for Proposals (with responses being assessed by government program managers). However, more flexible announcements are required for the external basic research program to ensure influx of innovative ideas and creative approaches to established research areas. Peer-review, involving scientists who are both scientifically and programmatically knowledgeable, ensures a healthy program that captures cutting edge approaches and avoids entrenchment.

3. An effective national program requires close coordination of the DoD program with DOE and the operational effort at the National Data Center, which is run by the Air Force Technical Applications Center (AFTAC). It is also important to sustain strong lines of communication with research programs in other agencies (such as the USGS, NSF, and NOAA) which provide basic and applied research advances and even operational products (e.g. precise earthquake bulletins and weather pattern models) that can augment CTBT monitoring. Such coordination would be enhanced if there is open access to the IMS data.

The panel will review and evaluate the content and focus of the research support programs of seismology of the Air Force Office of Scientific Research and the Phillips Laboratory of Hanscom Air Force Base.

Soon after the panel began to work on this charge, the Department of Defense announced plans to eliminate the AFOSR and Phillips Laboratory external research program in seismology. The following paragraphs summarize the panel's review of the programs before the study was modified in response to the charge from NTPO.

The AFOSR program used a Broad Agency Announcement (BAA) procedure for soliciting proposals on a broad range of seismological research problems. From 1993–1996 $3.3M/yr of grants/contracts were issued by the 6.1 program with $0.5–0.9M/yr provided to the AFPL to partially support an internal research effort in seismology. The AFOSR program used proposal peer review and relevance reviews by AFTAC and ARPA, with funding decisions based on a combination of value and relevance. The funding for this program was unstable, with annual budget difficulties; however, 57 total grants/contracts were issued. This program bolstered university involvement in CTBT-relevant research, which had diminished significantly as ARPA focused effort on systems development. Research activities conducted by the universities under the AFOSR program included research on regional distance seismograms, elastic and anelastic structure in Eurasia, Africa, the Middle East, and South America, characteristics of Lg propagation, basic wave propagation theory for calculation of regional high frequency phases, source radiation effects in anisotropic media, three component waveform analysis, and numerous other topics relevant to CTBT research. High priority was given to discrimination and location research, moderate priority to magnitude estimation, and relatively low priority to detection and regionalization efforts. Notably, the panel's review of research issues in seismology gives high priority to the last two issues.

The function of transitioning the research developments from the basic (6.1) research program to the operational regime was tasked to the 6.2 program at AFPL. By FY96 the AFPL program involved 8 civil servants and 7 on-site contractors performing directed research efforts. The AFPL budget, mainly for external contracting, was provided by AFOSR, AFPL, AFTAC, ARPA, the Arms Control and Disarmament Agency (ACDA), the State Department and DOE. The FY95 budget for AFPL was $11.3M ($0.72M AFOSR; $1.05M AFPL; $2.74M AFTAC; $2.37M ARPA; $0.6M State Dept.; $3.67M DOE; $0.15M ACDA), and the FY96 budget was $9.74M ($0.9M AFOSR; $0.75 AFPL; $1.74M AFTAC; $1.81 ARPA; $4.40 DOE; $0.15 ACDA). The AFTAC, ARPA, and DOE support administered by AFPL and complemented by grants from the AFOSR 6.1 program, constituted the main research funding support base at universities and some contractors for basic and applied research in CTBT monitoring. The associated total levels were about $12M/yr for FY95 and FY96. Additional support for systems development and advanced developmental research were provided directly by ARPA, AFTAC, and DOE. These funds primarily supported private companies.

In 1996, the AFOSR and Phillips Laboratory (AFPL) programs in CTBT monitoring were eliminated as part of a restructuring of DoD programs in response to changing priorities. While AFTAC continues to be tasked with serving as the CTBT NDC, the AFOSR, AFPL and ARPA research budgets for FY 1997 were consolidated into a single DoD funding line, organized under the new Nuclear Treaty Program Office (NTPO), overseen by the Assistant to the Secretary of Defense for Nuclear, Chemical and Biological Programs.