National technical means of verification (NTM) are monitoring techniques, such as satellite photography, used to verify adherence to international treaties. The phrase first appeared, but was not detailed, in the Strategic Arms Limitation Treaty (SALT) between the US and USSR. At first, the phrase reflected a concern that the "Soviet Union could be particularly disturbed by public recognition of this capability [satellite photography]...which it has veiled." In modern usage, the term covers a variety of monitoring technologies, including others used at the time of SALT I.
It continues to appear in subsequent arms control negotiations, which have a general theme called "trust but verify". Verification, in addition to information explicitly supplied from one side to the other, involves numerous technical intelligence disciplines. Measurement and Signature Intelligence (MASINT) techniques, many being especially obscure technical methods, are extremely important parts of verification.
Outside of treaties, the techniques described here are critical in overall counterproliferation work. They can gather information on the states, with known or presumed nuclear weapons, that have not ratified (or are withdrawing from) the Nuclear Non-Proliferation Treaty: India, Israel, North Korea, and Pakistan.
While the techniques here are focused primarily at missile and nuclear weapons limitation, the general principles hold for verification of treaties to counter the proliferation of chemical and biological warfare capabilities: "trust but verify".
Imagery intelligence
Imagery intelligence (IMINT) taken by satellites (e.g., US CORONA, KH-5, etc.) covert high-altitude reconnaissance aircraft (e.g., Lockheed U-2) and drones/unmanned aerial vehicles (e.g., Global Hawk), and sensor-carrying aircraft allowed by treaty (e.g., OC-135B Open Skies), is a fundamental method of verification. Specific "protocols" spelling out the details of treaty implementation may require cooperation with IMINT, such as opening the doors of missile silos at agreed-to times, or making modifications to aircraft capable of nuclear weapons delivery, such that these aircraft can be identified in photographs.
These methods provide an actual count of delivery vehicles. Although they cannot look inside and count warheads or bombs.
Interpretation involves art, science, and experience. For example, US intelligence used a discipline called "crateology" to recognize Soviet missiles and bombers, from the distinctive way the Soviets crated them for ocean shipment. Dino Brugioni gives an extensive account of imagery interpretation during the Cuban Missile Crisis in his book, Eyeball to Eyeball. The methodology he describes for counting missiles moving into Cuba, emplaced there, and later removed are direct parallels to the way in which imagery is used for verification in arms control.
Telemetry intelligence Telemetry intelligence (TELINT) is one of the "national means of technical verification" under the Strategic Arms Limitation Treaty (SALT). TELINT collects and analyzes the signals transmitted during missile tests, providing direct measurements of a missile's flight characteristics—most importantly its throw‑weight, which determines the potential mass of its nuclear warheads. SALT I obliges each party "not to interfere with national technical means of verification" and prohibits "deliberate concealment measures to impede verification," a clause that effectively bars encrypting or otherwise obscuring strategic test telemetry to thwart TELINT monitoring.
Electro-optical and radar sensors in verification
Telemetry intelligence on a missile test is frequently combined with electro-optical intelligence and radar tracking from cameras on aircraft (e.g., US RC-135 COBRA BALL), ground stations (e.g., US Cobra Dane) and ships (e.g., US Cobra Judy, Cobra King, Cobra Gemini). Observed trajectories, speeds, etc., can be used to verify the TELINT information is accurate. Even though some of these techniques do take pictures, these, as a whole, are considered MASINT.
Methods continue to evolve. COBRA JUDY was intended to gather information on long-range missiles, in a strategic role. One developmental system, COBRA GEMINI, was intended to complement COBRA JUDY. It can be used for observing long-range missiles, but is also appropriate for theater-level weapons, which may be addressed in regional arms limitation agreements, such as the Missile Technology Control Regime (MCTR). Where COBRA JUDY is built into a ship, this dual frequency (S- and X-band) radar is transportable, capable of operating on ships or on land, and optimized for monitoring medium range ballistic missiles and antimissile systems. It is air-transportable to deal with sudden monitoring contingencies. Cobra Gemini was installed aboard around 2000.
Cobra King was the Cobra Judy replacement that entered service on in 2014.
Space-based nuclear energy detection
In 1959, the US started to experiment with space-based nuclear sensors, beginning with the VELA HOTEL satellites. These were originally intended to detect nuclear explosions in space, using X-ray, neutron and gamma-ray detectors. Advanced VELA satellites added devices called bhangmeters, which could detect nuclear tests on earth by detecting a characteristic signature of nuclear bursts: a double light flash, with the flashes milliseconds apart. These satellites also could detect electromagnetic pulse signatures from events on Earth.
Several more advanced satellites replaced the early VELAs, and the function exists today as the Integrated Operational Nuclear Detection System (IONDS), as an additional function on the NAVSTAR satellites used for GPS navigation information.
Space-based staring infrared sensors
The US, in 1970, launched the first of a series of space-based staring array sensors that detected and located infrared heat signatures. Such signatures, which are associated with measurement of energy and location, are not pictures in the IMINT sense. Currently called the Satellite Early Warning System (SEWS), the program is the descendant of several generations of Defense Support Program spacecraft.
Originally intended to detect the intense heat of an ICBM launch, this system proved useful at a theater level in 1990–1991. It detected the launch of Iraqi Scud missiles in time to give early warning to potential targets.
When an arms control agreement, such as the MCTR, limits missile technology transfer, this system can detect missile launches that may have been a result of inappropriate transfer, or independent development by a nation that has not imported rocket motors.
Geophysical intelligence
US Army Field Manual 2-0 defines geophysical intelligence as a branch of MASINT. "It involves phenomena transmitted through the earth (ground, water, atmosphere) and manmade structures including emitted or reflected sounds, pressure waves, vibrations, and magnetic field or ionosphere disturbances."
Seismic intelligence
US Army Field Manual 2-0 defines seismic intelligence as "The passive collection and measurement of seismic waves or vibrations in the earth surface." In the context of verification, seismic intelligence makes use of the science of seismology to locate and characterize nuclear testing, especially underground testing. Seismic sensors also can characterize large conventional explosions that are used in testing the high-explosive components of nuclear weapons.
In 1960, George Kistiakowsky introduced the "threshold principle" that balances the needs of arms control with the realities of seismic verification. He cited the difficulty in monitoring missile submarines, and proposed that the arms control strategy focus on disarmament rather than inspections into verification, which accepts that nations may do nuclear, or simulated nuclear, testing of an explosive yield below the energy level that seismic intelligence sensors can detect. All nuclear testing, of any level, was forbidden under the Comprehensive Test Ban Treaty (CTBT) (which has not entered into force), but there is controversy over whether the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) or its preparatory commission will be able to detect sufficiently small events. It is possible to gain valuable data from a nuclear test that has an extremely low yield, useless as a weapon but sufficient to test weapons technology. CTBT does not recognize the threshold principle and assumes all tests are detectable.
The CTBTO will operate an International Monitoring System (IMS) of MASINT sensors for verification, which include seismic, acoustic, and radionuclide techniques. It is controversial if the IMS will be able to detect all events.
Bailey are concerned that "Opponents of the CTBT are most concerned about one issue: in the absence of nuclear testing, U.S. nuclear weapons can be neither as safe nor as reliable as they should be. … While the treaty will constrain the United States from modernizing and developing weapons, it will be possible for other nations to cheat with little or no risk of being caught because the CTBT cannot be verified....The IMS of the CTBT is expected to provide the ability to detect, locate, and identify nonevasive nuclear testing of yields of 1 kiloton or greater. It will not beable to detect, with any significant degree of confidence, nuclear testing below 1 kiloton. If the test is evasively conducted, the system will not detect a test of several kilotons."
Advocates of the CTBT Paine argues "...there is recent demonstration that the IMS will be able to detect and identify non-evasive explosions of less than 1 kiloton in some strategically important areas." Initial indications, in August 1997, pointed to a seismic event in Novaya Zemlya, which is Russia's main test site. At first, it was believed to be a hidden nuclear test. IMS sensors, however, helped locate the event offshore, in the Kara Sea. IMS also established that it was an earthquake, not an explosion.
"Had this been an underground nuclear test, its magnitude (3.3) would have corresponded to a yield of less than 100 tons (0.1 kilotons) in the absence of evasive measures. A nearby event identified as an earthquake in January 1996 was a factor of ten smaller (2.4), corresponding to a yield of about 10 tons." Opponents of the IMS had claimed the best that could be done was to recognize a 1 kt event, not concealed and of Richter magnitude 4.0.
Paine seems to assume that tests will still be in a plausible weapons range, and a 10-ton yield still might be useful in some tactical applications. There is a class of applied research testing, hydronuclear tests, that yield useful information but have a yield as low as a kilogram, up to low tons. Hydronuclear tests do involve nuclear reactions, but very small ones. A technique that actually may have more explosive yield, of high explosive, is hydrodynamic testing, in which extremely fast X-ray, neutron, or other specialized camera measure, in microseconds, the explosive compression of a fissionable material simulant. Depleted uranium, for example, has the same physical properties as enriched uranium, and is similar to plutonium.
Acoustic intelligence
Sensors relatively close to a nuclear event, or a high-explosive test simulating a nuclear event, can detect, using acoustic methods, the pressure produced by the blast. These include infrasound microbarographs (acoustic pressure sensors) that detect very low-frequency sound waves in the atmosphere produced by natural and man-made events.
Closely related to the microbarographs, but detecting pressure waves in water, are hydro-acoustic sensors, both underwater microphones and specialized seismic sensors that detect the motion of islands.
On-site inspection