to locate, the infrasound system will be confronted with far fewer events, but it could play an important role in identifying surface sources such as quarry blasts, as well as monitoring atmospheric events. The air disturbance from an atmospheric blast can also perturb the ionosphere, producing a propagating, large-amplitude deflection of the ionosphere that could be detectable by radiowave sensors, which reflect signals from the ionosphere, or by Global Positioning System (GPS) stations at the surface, which detect changes in the total electronic count associated with a frequency-dependent time delay. Such sensors are not part of the IMS.

Atmospheric blasts release radioactive particulates and gases that are transported by the wind. If the blast is near the Earth's surface, a cloud of dust, hot gas, and debris can rise with the vortex formed by the fireball, injecting debris into the upper atmosphere. Fission products and other vapors condense on soil and debris particulates, with the heavier particulates settling out near the source while lighter ones can be carried downwind (see Appendix G for more details). Explosions over water close enough to the surface for water to be vaporized by the fireball will have a large amount of local fallout as the fission products are washed out of the air, first with the descending water column, then with the resulting mist, and then in rain as the vaporized water recondenses (Glasstone, 1957). Radionuclide detectors at the surface will detect the particulates and radiogenic noble gases that are produced by atmospheric nuclear explosions, with wind patterns determining which stations "see" the event and at what time. Wind transport velocities are relatively slow (compared to sound waves); thus, radionuclide detections may take days to weeks, depending on source location, weather patterns, and the location of the nearest fixed station. The radioactive decay with time and the reduction in concentration due to various mechanisms as the material spreads out reduce the detectability of the material. Rain-out can rapidly reduce particulate concentrations, so the opportunity to observe the debris is time-limited. Rain-out will have little effect on the concentration of radioactive noble gases; so the monitoring of these gases is important. Radionuclide observations can be reliable indicators of an atmospheric test if the material is collected and analyzed early enough.

Near-surface atmospheric explosions can couple energy from atmospheric sound waves into the ocean or solid Earth. Thus, there is some role for hydroacoustic and seismic monitoring of explosions in the atmosphere, particularly in the case of evasion scenarios that attempt to mask the explosion by near-surface detonation (e.g., testing near the surface on a cloudy day with strong rains and certain masking efforts).

Underwater nuclear tests are a major concern because, like atmospheric tests, they could potentially

Front Matter (R1-R12)

Executive Summary (1-6)

1 Introduction: The Comprehensive Nuclear Test Ban Treaty (7-22)

2 CTBT Monitoring Technical Challenges That Drive Research (23-48)

3 Monitoring Technologies: Research Priorities (49-82)

4 U.S. Research Infrastructure (83-88)

5 Conclusions and Recommendations (89-96)

References (97-100)

Appendix A: Statement of Task (101-102)

Appendix B: Research Support History (103-106)

Appendix C: Seismic Event Location (107-112)

Appendix D: Seismic Magnitudes and Source Strengths (113-120)

Appendix E: Hydroacoustics (121-124)

Appendix F: Infrasonics (125-130)

Appendix G: Radionuclide Source Term Ranges for Different Test Scenarios (131-136)

Appendix H: Acronyms (137-138)