Remote Monitoring: Verifying geographical arms limits

By Moritz Kütt, Ulrich Kühn, Dmitry Stefanovich | January 16, 2023

Safeguards inspectors setting up a camera for round-the-clock surveillance of operations at the Dukovany Nuclear Power Plant in the Czech Republic. Image courtesy of D. Calma/IAEA.

Remote Monitoring: Verifying geographical arms limits

By Moritz Kütt, Ulrich Kühn, Dmitry Stefanovich | January 16, 2023

Europe’s biggest security crisis of recent decades has brought back fear of nuclear use, nuclear war, and arms racing. Conversely, arms control with Russia looks like an afterthought right now, given the harsh realities. But new types of missiles, an adversarial NATO-Russia relationship, and the ever-present threat of inadvertent escalation make it necessary to start thinking anew how verifiable arms control with Russia may look like in the future.

Shortly before the Russian military’s attack on Ukraine’s forces, Russia brought to the table a draft treaty to NATO member states, suggesting that both sides commit to “not deploy land-based intermediate- and short-range missiles in areas” where they could reach Russian and NATO territories (MID 2021). The proposal built on earlier Russian ideas for a missile deployment moratorium for the entirety of geographical Europe (President of Russia 2020). In response, the United States stated its readiness “to begin discussions … on arms control” for such systems (Arbide Aza and González 2022).

Though subsequent events ended the short-lived dialogue, these diplomatic overtures were the first after the 2019 US decision to withdraw from the Intermediate-Range Nuclear Forces (INF) Treaty with Russia. Signed in 1987, the treaty mandated the elimination of all of the former super powers’ land-based missiles and launchers with ranges between 500 kilometers and 5,500 kilometers (roughly about 300 miles and 3,418 miles). The reasons for the end of the INF are manifold. Moscow developed and deployed new, allegedly INF-range missiles in secret. Both parties showed a lack of creativity searching for efforts to resolve this issue. In addition, China is building up its missile inventory, especially in intermediate ranges.

Intermediate-range missiles are destabilizing because of their very short flight times. During the Cold War, flight times were often well below 10 minutes (Hughes 2009), depending on the type of missile and its launch point. Without the INF Treaty, arms racing has become much more likely in Europe and Asia. Even if Washington and Moscow could agree on a new mechanism to limit such weapons, the question would be how to verify compliance with such an agreement.

The answer could be remote monitoring with “active tags” that broadcast a signal showing the location of a missile or other weapon system. With today’s technology, not only could active tags help to monitor missiles remotely; they could also make verification of certain geographical arms limits possible. Such limits would not be an immediate disarmament measure requiring the verified dismantlement of weapons, but rather a means to regain confidence in politically difficult times and to buy time for diplomacy in an escalating crisis between Russia and NATO. Using remotely monitored tags would furthermore greatly reduce reliance on in-person on-site inspections.

We present a menu of options for states that could be applicable to any area around the globe and even cover certain types of sea- and air-launched missiles that were never subject to arms control limitations. That way, verifying geographical arms limits could be a starting point for more comprehensive disarmament.

Active tags instead of inspections

Past arms control accords have shown that the most reliable way to determine the physical location of a weapon is by inspections. Under INF, a number of select missile production, test, storage, and elimination facilities—as well as designated main operating bases and deployment zones in the United States, Europe, and the Soviet Union—became subject to on-site inspections. The treaty initially allowed up to 20 short-notice inspections per year. Another Cold War accord, the 1990 Treaty on Conventional Armed Forces in Europe (CFE) also relied heavily on inspectors’ boots on the ground to verify specific geographical limits on conventional arms. In addition to on-site inspections at declared sites, so-called challenge inspections allowed inspectors to visit undeclared sites at short notice.

Inspections come with difficulties. Since the host has to grant the inspecting party access to its military sites, a precondition to inspections is a certain level of trust. Inspections are also time consuming and resource intensive. In times of a virus pandemic, physical access might be all but impossible. Remote monitoring with active tags could significantly reduce the necessity for on-site inspections and, at the same time, increase the level of confidence in verification, at lower cost and without the intrusiveness of foreign inspectors. Although ideally active tags would be combined with regular inspections, their separate use would be an important transparency measure and a significant interim step that could help the United States, Russia, and NATO regain trust.

Utilizing today’s technology, we revisit the idea of active tags and suggest their application for an entirely novel purpose: to monitor geographical deployment limits. In past arms control contexts, tags attached to objects have usually been used for their identification, similar to license plates in traffic. Compliance was verified through inspections. Early proposals for the use of active tags allowing for remote monitoring focused exclusively on verifying numerical limits (Fetter and Garwin 1989). In the pre-GPS era, Sidney Drell and his colleagues introduced so-called proximity tags that would send a radio signal to a satellite system of the monitoring party (Drell et al. 1990). Tags to help limit mobile missile numbers were also discussed during past US-Russian negotiations on strategic nuclear arms.

The process of active tagging could look as follows: First, an active tag is mounted to a weapon―say, a road-mobile missile launcher. The monitoring party would observe this process. Such an observation could be considered an “easy” inspection—it could take place at a location freely chosen by the host, away from sensitive military installations. Afterward, the tag would broadcast a specified signal, allowing the monitoring party to remotely establish the weapon’s geographic location and to evaluate if a violation of geographical limits for deployment had occurred.

The process sounds straightforward, but implementing it would in fact require making a number of difficult technical and political choices.

The nuclear year in review: A renewed interest in nuclear weapons—for and against

Balancing competing interests

The monitoring party and the monitored state in an arms control agreement have different, often competing interests. While the monitoring party wants to keep cheating possibilities to a minimum, the monitored state is usually coy about disclosing too much military information, wary that verification become intelligence-gathering.

Monitoring can also negatively affect what arms control experts call “crisis stability.” For the monitor, not knowing the location of a weapon at any given time may raise suspicion and be interpreted as non-compliance or worse. For the monitored, revealing a weapon’s exact location, particularly over long periods, may turn it into an attractive target. During a crisis, pressures could mount on both sides: A monitoring country could decide to attack those weapons early, or the monitored country could decide to use them preemptively before they come under attack.

Asymmetries in weapons holdings between monitor and monitored can make this stability dilemma worse. China, for instance, resists all calls for transparency about its nuclear forces because it fears that it would give the United States—with its 15-times-larger nuclear arsenal—a significant advantage in a first strike.

Entirely solving these perennial trade-offs between national security, compliance, and crisis stability is impossible. But a good monitoring protocol—jointly negotiated and using active tagging—could help balance some of the aforementioned competing interests.

How active tagging would work

To make a verification system that uses active tagging effective, the countries involved would have to carefully define the terms and conditions of the tagging regime in terms of safety, location, timing, frequency, and control.

To address safety concerns, ideally the parties would design the active tag jointly. Once completed, the tag’s interior would not be accessible to the monitored party. The tagging mechanism would have to be designed so breaking and tampering with it would be detectable by the monitoring country. The tag would of course be attached to the weapon to be monitored, but for certain weapons—for example, cruise missiles—attaching the tag directly to the weapon could affect its function. In such cases, transport-launch canisters or the missile launcher should be tagged instead.

In terms of location, a country will resist allowing an adversary to know precisely where its weapons are located at particular times—even if geographical location is part of an arms control agreement. One solution to this dilemma: A least-information possible, “inside/outside” approach, with the weapon being either inside or outside a defined area. NATO allies might be interested to know where Russia’s suspected missiles are not―that is, in the European part of Russia, west of the Ural Mountains. Russia may find it more attractive to have confidence that possible future US INF-range missiles, once developed and produced, are not moved to Europe.

An active tag could either transmit its current position in real-time or relay only past locations. The latter—a deliberate delay, even if only a few hours, of information on a weapon’s location—would create a window of opportunity for diplomacy should an unintentional violation or device malfunction occur.

A delay could also protect very sensitive locations from the monitor’s eyes. It could, however, also give the monitored party first-mover advantages in a military crisis. So the transmission of location data would be a matter for negotiation: It could be continuous, come periodically, at pre-defined intervals, or be initiated sporadically, upon request. Again, more data would benefit the monitoring party. In any case, it would be important to ensure that the data transmission itself could not be used by countries not part of the agreement. Location information should be kept out of the hands of third parties by limiting the initial transmission range for the tag. Other channels—including, for example, existing telecommunication infrastructure—could then relay the signal on to the monitoring country.

The monitored party inevitably holds full physical control of the tag. All other aspects of decision and control would be subject to negotiation. The monitored party could have complete power of decision through the ability to turn the tag on or off. Alternatively, the monitored party would only control partial functions―either the location estimation or the transmission process. Parties could also agree on a scheme that would automatically trigger transmission based on specific events that might indicate possible military use, such as the tag moving for several successive days. In an even more fine-grained approach, in which past location data is recorded and transmitted, the monitored party could hold the right to withhold information on periods of maintenance or military exercises.

All those aspects are interdependent and allow for compromises during negotiations. For example, if location transmissions were set up as continuous and in real-time, the monitored party would likely only allow general information on whether the weapon were inside or outside a particular region to be transmitted. In contrast, if the monitored party were willing only to share data recorded in the past, more precise location information could convince the monitor that no violation has occurred since. In the current European theater, remotely monitoring some of Russia’s new missiles in an “inside/outside” approach―with the Ural Mountains representing the boundary line―could significantly enhance predictability and confidence in the West, without putting Russian missiles at risk of preemptive attack. The same could be true for the Russian concerns as regard possible future US missile deployments to Europe.

What geo-location technology could be used?

The parties to an arms control agreement that included an active tagging component would have to weigh the pros and cons of different geo-location technologies. Since the end of the Cold War, global geo-location services have become ubiquitous, in particular because of the widespread use of smart phones. Today, the most common way to determine the location of an object on Earth is by using Global Navigation Satellite Systems (GNSS) such as America’s “GPS,” “GLONASS” by Russia, “Galileo” by the European Union, or “Beidou” by China. In all these systems, satellites continuously transmit data packages that include time of transmission to the various receivers―built into cell phones or, in the case we’re now discussing, active tags―which then determine their own location with an uncertainty of usually less than 10 meters. For verifying regional geographical arms limits, an uncertainty of the order of kilometers would be sufficient.

United States nuclear weapons, 2024

The major downside of GNSS-based approaches is their vulnerability. They can, for instance, be subject to spoofing attacks, in which the original signal is overlaid with an authentic-looking signal showing a different location (Harris 2019). Existing commercial satellite receivers are susceptible to such attack, but ongoing research shows that receivers equipped with multiple antennas are able to detect spoofing (Magiera 2019).

An alternative to GNSS involves a different type of satellite tracking system, in which the active tag would transmit a unique signal, making it possible to triangulate the position of the sender using multiple receivers. The precision of such a system would be on the order of tens of kilometers, but still sufficient for NATO to determine that Russian missiles are not in the country’s Western part or for Russia to know that US missiles are not in Europe.

The monitoring party could choose a commercial operator with global satellite coverage. Private vendors like Iridium already include a Doppler shift-based estimate of the sender’s location and offer ready-to-use devices for a few hundred dollars. National leaders and defense officials might not be ready to entrust a private vendor with services highly critical to national security. But non-commercial alternatives are available, including national intelligence and reconnaissance satellites and the communications network of the Comprehensive Nuclear-Test-Ban Treaty Organization, a multilateral arms control body.

Geolocation is also possible with an Inertial Navigation System (INS), which uses measurements provided by accelerometers and gyroscopes to track the position and orientation of an object relative to a known starting point. Because of its internal workings, however, an INS will gradually accumulate errors and must be reset to a known location within periodic intervals.[1]

In the past, INSs with suitable precision were limited to mechanical devices used by submarines for navigation or in nuclear-tipped missiles and launch systems. These old systems are expensive and rather large. Today, micro-electromechanical systems, however, reach bias stabilities within two orders of magnitude of mechanical gyroscopes, and an order of magnitude for their associated accelerometers (Schmidt 2019). Furthermore, they are relatively small, inexpensive, and can operate with limited power supplies—features necessary for small, active tags.

Thinking beyond the INF

The next round of nuclear arms racing—this time involving Russia, the United States, and China—has already started. Marshall Billingslea, the highest-ranking arms control negotiator in the previous U.S. administration, threatened to spend Russia and China “into oblivion” in order to win a new nuclear arms race (Reuters 2020). Meanwhile China has increased the number of its strategic missile silos and tested a new type of strategic delivery vehicle (Sanger and Broad 2021). Geopolitics seems to dictate that both Russia and China will continue to rely on missiles with ranges that could target their immediate neighborhood, including US military installations in allied countries. In the years to come, Washington could respond with the deployment of a new generation of intermediate-range missiles in Europe and East Asia.

All that happens against the background of ongoing fighting in Ukraine and years and years of previous crisis in arms control diplomacy. Our proposal to monitor remotely certain geographical arms limits would present a technical solution at much lower cost than a comprehensive on-site inspection scheme. Thinking beyond the current crisis in Europe, our proposal could as well be applied to other regions, for example in East Asia. As a step towards the denuclearization of the Korean peninsula, North Korea could agree to store its warheads and delivery systems separately in different regions—monitored by active tags. The same technology could contribute to confidence building along the Indo-Pakistani border or between China and India. In all these cases, countries deploy short and medium-range missiles. Crisis stability could be strengthened were those weapons moved away from opponents’ borders in a verifiable manner. In addition to ground-launched missile systems, the usage of active tags could also be extended to cover sea- and air-launched missiles and their respective launchers.

Innovative technical solutions, like modern geo-location technology, might help rebuild confidence in an increasingly dangerous environment of great power rivalry. Ideally, states might follow up with numerical limits or even bans on particular weapons categories. In the end, technology could be an enabler of future and more comprehensive disarmament measures.



[1] The monitoring party would only need confirmation that the active tag was reset at a particular location within an acceptable time when verifying a missile’s deployment—for example, by allowing the tag to communicate with a fixed base station at one of several verified points. Base stations would have to be installed in parallel to the distribution of active tags, and a reset confirmation could be stored either by the tag itself or a base station as a tag passes nearby. The confirmation would only later be revealed to the monitoring party. Location measurements (accurate to within 300 kilometers, or about 188 miles, in 24 hours) would then be possible by an INS with modest performance specifications (a gyro bias drift of 0.1 degrees/hour) without reliance on external signals or tracking systems controlled by either party. For monitoring large geographical arms limits—such as Russia’s ‘East of the Urals’ area—even uncertainties of the order of 100 kilometers (about 63 miles) might be acceptable.


This research was funded through the “Research and Transfer Project Arms Control and Emerging Technologies” by the German Federal Foreign Office.



Arbide Aza, H. and Miguel González. 2022. “US Offered Disarmament Measures to Russia in Exchange for Deescalation of Military Threat in Ukraine.” El Pais, February 2.

Drell, S. et al. 1990. “Verification Technology: Unclassified Version.” JASON Report, JSR-89-100A. Arlington: The MITRE Corporation.

Fetter, S. and Thomas Garwin. 1989. Using Tags to Monitor Numerical Limits in Arms Control Agreements. In Technology and the Limitation of International Conflict, edited by Barry M. Blechman, 33-54. Washington, DC: The John Hopkins Foreign Policy Institute.

Harris, M.. 2019. “Ghost Ships, Crop Circles, and Soft Gold: A GPS Mystery in Shanghai.” MIT Technology Review, November 15.

Hughes, K. 2009. “The Army’s Precision ‘Sunday Punch’: The Pershing II and the Intermediate-Range Nuclear Forces Treaty.” Army History 73: 6-16.

Magiera, J. 2019. “A Multi-Antenna Scheme for Early Detection and Mitigation of Intermediate GNSS Spoofing.” Sensors 19 (10): 2411.

MID (The Ministry of Foreign Affairs of the Russian Federation). 2021. Agreement on Measures to Ensure the Security of the Russian Federation and Member States of the North Atlantic Treaty Organization.

President of Russia. 2020. Statement by Vladimir Putin on Additional Steps to De-escalate the Situation in Europe after the Termination of the Intermediate-Range Nuclear Forces Treaty (INF Treaty), October 26.

Reuters. 2020. “U.S. Prepared to Spend Russia, China ‘Into Oblivion’ to Win Nuclear Arms Race: U.S. Envoy.” Reuters, May 21.

Sanger, D.E. and William J. Broad. 2021. “As China Speeds Up Nuclear Arms Race, the U.S. Wants to Talk.” The New York Times, November 28.

Schmidt, G.T. 2019. “GPS Based Navigation Systems in Difficult Environments.” ˆ 10: 41-53.

Together, we make the world safer.

The Bulletin elevates expert voices above the noise. But as an independent nonprofit organization, our operations depend on the support of readers like you. Help us continue to deliver quality journalism that holds leaders accountable. Your support of our work at any level is important. In return, we promise our coverage will be understandable, influential, vigilant, solution-oriented, and fair-minded. Together we can make a difference.

Get alerts about this thread
Notify of
1 Comment
Newest Most Voted
Inline Feedbacks
View all comments
Rob Goldston
Rob Goldston
1 year ago

Bravo! Indeed we need to be offering approaches for renewed INF & CFE agreements (not to mention an ABM agreement, etc.) to give Putin a politically viable exit from Ukraine, per .