Several on-site inspection regimes include provisions for the on-site monitoring by inspectors of particularly sensitive facilities or sites to confirm that they are complying with treaty requirements. Monitoring differs from other types of on-site inspection in that it involves a protracted or “continuous” presence of the monitoring team and/or technical monitoring equipment at a specific location on the soil of the inspected party. The technical monitoring equipment can range from seismic monitoring equipment emplaced to monitor a specific test to the emplacement and continuous observation of an array of technical sensing and measuring equipment located at the portal and around the perimeter of a facility.
The earliest long-term monitoring regimes involve containment and surveillance measures developed as part of the International Atomic Energy Agency's (IAEA) safeguards regime. The strengthened verification provisions added to the agreements to monitor the Threshold Test Ban Treaty (TTBT) and the Peaceful Nuclear Explosions Treaty (PNET) provide for on-site yield measurements of nuclear explosions and the establishment of seismic stations on Russian and U.S. territory for on-site monitoring. However, these new verification provisions were used only once early on, since, after their signature, both sides first adopted nuclear testing moratoria, then signed the Comprehensive Test Ban Treaty (CTBT) which establishes a global nuclear test ban.
The most elaborate and complex long-term on-site monitoring regimes developed and implemented to date are the portal and perimeter continuous monitoring (PPCM) systems established by the Intermediate-Range Nuclear Forces (INF) and Strategic Arms Reduction (START) treaties. These are designed to continuously monitor missile production at designated missile plants in the United States and the former Soviet Union (FSU). Conceptually, they use a team of on-site monitors, supported by monitoring equipment, to continuously observe shipments leaving the monitored facility to confirm that they are in accordance with treaty provisions. The monitoring equipment is located at the