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A nuclear detonation detection system (NDDS) is a device or a series of devices that are able to tell when a nuclear explosion has occurred as well as the direction it came from. The main purpose of these devices or systems was to make sure that countries that signed nuclear treaties such as the partial test ban treaty of 1963 (PTBT) and the Treaty of Tlatelolco.

There are many different ways to detect a nuclear detonation these include seismic detection, hydroacoustic, infrasound, air samples, and satellites. Each have been used separately but as of recently best results occur when data is used in tandem since the energy caused by an explosion will transfer over to different mediums. .

History
The partial test ban treaty banned nuclear testing in the atmosphere, underwater, and in outer space. The U.S. developed many different devices to ensure the Soviet Union were upholding their part of the treaty.

The partial test ban treaty aimed to ban underground testing as well but at the time the technology could not detect detonations very well with seismographs let alone differentiate them from earthquakes making them more difficult to identify than atmospheric detonations or underwater. Larger yields could be differentiated but the smaller ones could not be. Even then larger explosions could be dampened by having a larger cavity in the ground. With the threat of the Soviet Union conducting underground detonations the U.S. pumped money into seismology research. A major accomplishment was made by Sheridan Speeth; by changing the seismographs into audible files one could differentiate between earthquakes and nuclear explosions just by listening to the difference. However due to his political beliefs his work was ignored. The main system for detecting underground detonations remained to have large numbers of monitoring stations but due to the difficulty in creating technology and the amount of stations needed the treaty allowed underground testing.

Another way of detecting a nuclear detonation is through air sampling; in nuclear explosions there are radioactive isotopes that get released into the air which can be collected by plane. Radionuclides include Americium-241, Iodine-131, caesium-137, krypton-85, strontium-90, plutonium - 239, tritium, and xenon. By sending planes over an area equipped with sensors they could reveal if there was a nuclear detonation but most air samples are taken at one of many radionuclide stations set throughout the world. Even underground detonations will eventually release radioactive gases most notably xenon to be detected. Although there are some flaws to this method; depending on where the explosion was air currents could move the gases or radionuclides in another direction. The process involves taking in air samples with a filter paper and the radioactive material is counted by a machine and analyzed by a computer. Which means if there is outside “noise” (other forms of radiation like some released from factories or nuclear plants) it can throw off the results. An example of air currents moving radioactive particles is the Chernobyl disaster. As the reactor started failing a large amount of radionuclides were released into the air which were then spread by air currents; leading to radiation that could be detected all the way in Sweden and other countries hundreds of miles away within a few days. The same occurred at the Fukushima Daiichi disaster. The spread of radioxenon gas, iodine -131, and ceasium – 137 could be detected at different continents many miles away

Satellites were also implemented during the cold war era to ensure no nuclear testing was going on. They relied on sensors that picked up radiation from nuclear detonations. Nuclear detonations always produced gamma rays, x-rays, and neutrons. The most notable of U.S. satellite nuclear detection include the VELA hotel project. There were 12 satellites built and each was equipped with X-ray, neutron, and gamma ray detectors. Satellites are now also equipped with cameras that are able to capture above ground explosions. With the advent of Global Position System (GPS) satellites have become an important method of detonation detection. A slight drawback to the satellite detection method is that there are some cosmic rays that emit neutrons could give false signals to the sensor There are 11 hydroacoustic stations that are setup to monitor any activity in the oceans. They were developed to ensure the ban on underwater testing ; because of water’s ability to carry sound they are very efficient. However, hydroacoustics have difficulties pinpointing the location of an explosion or event so the must be used with another method of detection such as the ones previously mentioned sensors. Another problem that hydroacoustics faces is the structure of the sea floor as well as islands that may block sound; sound travels the best through deep ocean meaning events near shallow water will not be detected as well.

Infrasound works by having multiple stations that use microbarometers measure for infrasonic waves due to explosions, volcanoes or other natural occurring events. As with other detection methods infrasound development was during the cold war. These stations were designed to detect up explosions down to 1 kiloton but after the PTBT atmospheric detonation detection was left to satellites. Although infrasound waves could travel across the earth multiple times they were very prone to being influenced by the wind and temperature variations. Long range infrasonic waves are difficult to differentiate (e.g. chemical explosion and a nuclear explosion).

With the Comprehensive Nuclear Test Ban Treaty (CTBT) this banned all forms of nuclear testing in an attempt to disarm and move away from nuclear weapons but it came old challenges such as how to ensure members would not cheat the treaty. The CTBT brought with it a new system, the International monitoring system (IMS), which uses 321 stations with sensors that use all the methods previously stated. Using collected data from each source to calculate detonations. IMS brings hydroacoustic and infrasound detections systems as well as seismographs and air samplers for radionuclides. All of this information is collected by the the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) which is stationed in Vienna, Italy.

Effectiveness
One of the first uses of the CTBTO and its detection systems showed itself effective when it was able to identify nuclear testing by India and Pakistan in May or 1998.

Another notable example is the North Korean testing. As most countries have given up nuclear detonation tests North Korea has attempted to create a powerful nuclear warhead. Due to North Korea’s secrecy it is up to IMS to give researchers the information needed to evaluate North Korea’s threats. Even their low yield (0.6 Kiloton) first attempt at a nuclear weapon was picked up and isolated in 2006