Glossary

H-phase

A type of sound wave in the water that is created by underwater explosions.  This includes natural occurrences, such as underwater volcano eruptions, as well as man-made explosions, including underwater nuclear explosions.

Half-life

The time in which one half of the atoms of a particular radioactive substance disintegrates. Measured half-lives vary from millionths of a second to billions of years. Also called physical or radiological half-life.

Hertz

The International System of Units (SI) base unit of frequency. One hertz means one per second. 100 Hz means one hundred cycles per second. The unit may be applied to any periodic event.

High alert

The state of readiness of nuclear forces sufficient to launch an immediate attack.

Highly enriched uranium (HEU)

Uranium in which the naturally occurring Uranium (U)-235 isotope (0.7 % in natural uranium) is increased to 20% U-235 or above. In HEU used in nuclear weapons, the U-235 isotope is usually increased to 90% or more. HEU is used in nuclear weapons and in some types of research and submarine propulsion reactors.

Horizontal proliferation

The spread of weapons of mass destruction to states that have not previously possessed them.

Hydroacoustic

Describes the study of sound waves in the water and its applications.

Hydroacoustic monitoring

The recording of signals that show changes in water pressure generated by sound waves in the water. These waves can be caused by a range of natural and man-made events. This monitoring technology is used to detect underwater nuclear explosions or nuclear explosions near the ocean surface or coast.   

Hydroacoustic network

An International Monitoring System network of eleven stations used to detect any underwater nuclear detonations. Two distinct sensing techniques are used. Six underwater microphones (hydrophones) capture acoustic waves propagating through large ocean areas and are quite complex and expensive to build.  Five “T-Phase” stations consist of seismic detectors located on small, oceanic islands that detect acoustic waves, which are converted to seismic waves once they hit land. These T-phase stations are less effective but considerably simpler and less costly to construct.

Hydroacoustic station

Monitors the big oceans for hydroacoustic waves to detect underwater nuclear explosions and distinguish them from other natural or man-made events.  There are two types of stations – hydrophone stations and T-phase stations. Hydrophone stations use hydrophones, essentially underwater microphones, to detect hydroacoustic waves. T-phase stations measure seismic waves that converted from hydroacoustic waves when hitting land.  These stations are usually located on oceanic islands.

Hydroacoustic stations

Monitors the big oceans for hydroacoustic waves to detect underwater nuclear explosions and distinguish them from other natural or man-made events. There are two types of stations – hydrophone stations and T-phase stations. Hydrophone stations use hydrophones, essentially underwater microphones, to detect hydroacoustic waves. T-phase stations measure seismic waves that converted from hydroacoustic waves when hitting land.  These stations are usually located on oceanic islands.

Hydroacoustic waves

Sound waves in the water. Hydroacoustic waves can be emitted by a range of natural events, i.e. earthquakes or underwater volcano eruptions, and man-made events such as underwater exploration activities or military exercises.

Hydroacoustics

Describes the study of sound waves in the water and its applications.

Hydrogen bomb

A weapon that uses nuclear fusion to provide explosive power. Also referred to as an “H-bomb” or a thermonuclear bomb. Such a bomb derives its destructive force from nuclear reactions of fission and fusion.As a result, even a nuclear weapon with a small yield is significantly more powerful than the largest conventional explosives, and a single weapon is capable of destroying an entire city. See also Fusion and Thermonuclear weapon.

Hydrogen bombs

Weapons that use nuclear fusion to provide explosive power. Also referred to as an “H-bomb” or a thermonuclear bomb. Such a bomb derives its destructive force from nuclear reactions of fission and fusion.As a result, even a nuclear weapon with a small yield is significantly more powerful than the largest conventional explosives, and a single weapon is capable of destroying an entire city. See also Fusion and Thermonuclear weapon.

Hydrophone

An underwater microphone that detects hydroacoustic waves, i.e. sound waves, in the water.

Hydrophone sensor

An underwater microphone that detects hydroacoustic waves, i.e. sound waves, in the water.

Hydrophone sensors

Underwater microphones that detect hydroacoustic waves, i.e. sound waves, in the water.

Hydrophone station

A monitoring station using an underwater microphone (hydrophone). The station receives and records underwater acoustic signals originating from submarines, volcanic eruptions, earthquakes and underwater explosions. The data, sent out via cable to the shore station for analysis, are used to distinguish between underwater explosions and other phenomena. Due to their complex set-up involving underwater sensors and long stretches of cables, these stations are costly to build. 

Hydrophone stations

Monitoring stations using an underwater microphone (hydrophone). Stations receive and record underwater acoustic signals originating from submarines, volcanic eruptions, earthquakes and underwater explosions. The data, sent out via cable to the shore station for analysis, are used to distinguish between underwater explosions and other phenomena. Due to their complex set-up involving underwater sensors and long stretches of cables, these stations are costly to build.

Hydrophones

Underwater microphones that detect hydroacoustic waves, i.e. sound waves, in the water.