ENCYCLOPEDIA OF Espionage, Intelligence, and Security Volume ...

Electromagnetic Spectrumbecause the Soviet Union had already conducted highaltitudetests like Starfish. HEMP subsequently became acentral component in strategic nuclear war-simulations;many speculative scenarios for a Soviet first strike on theU.S. began with an EMP “lay-down” created by simultaneouslyexploding a relatively small number of nuclearweapons at high altitude over the United States. The goalwould have been to cause widespread damage to civilianand military electrical and electronics systems at relativelylow cost, to be followed by a more devastating groundattack. More recently, some U.S. officials considered asmaller-scale EMP laydown attack on Iraq as a prelude tothe Gulf War of 1990. (The attack was not carried out.)Although some planners have worried that a nationor terrorist group possessing only a few nuclear weaponsmight use one of them to blanket the U.S. with a damagingHEMP, this is thought by most experts to be unlikely. Tocreate a significant HEMP attack, a weapon must be smallenough to be lofted on a ballistic missile, and few countrieshave the know-how either to make powerful nuclearweapons of such small size or to build ballistic missiles. Inany case, it is unlikely that an adversary seeking to causemaximal harm and willing to risk using nuclear weaponsagainst a nuclear-armed adversary such as the U.S. wouldmake a HEMP attack. Any nuclear weapon would cause farmore destruction by direct blast (if detonated over or in acity) than by HEMP (if detonated at high altitude).Besides HEMP, two other forms of electromagneticpulse may be caused by nuclear explosions. The first isgenerated inside electronic devices by the passage ofionizing radiation (e.g., neutrons and gamma rays) directlyinto metallic cases, circuit boards, semiconductorchips, and other components, where it can cause briefelectrical currents to flow by knocking electrons loosefrom atoms. This effect is termed systems-generated electromagneticpulse (SGEMP). The other form of EMP—source-region EMP or SREMP—occurs when a nuclearweapon explodes at low altitude. In this situation, a highlyasymmetric electric field is produced in the vicinity of theburst (e.g., within a radius of 3–8 km) having intensitiesthat are much greater than those produced by HEMP.Since the region affected by SREMP corresponds to thateffected by the nuclear blast itself, SREMP is relevant onlyto the defense of hardened targets such as buried missilesilos, which are intended to remain functional even in theaftermath of a near-surface nuclear blast.Carbon-graphite coils capable of generating an electromagneticpulse used to destroy electronics equipment—especially communications equipment—can be fitted tocruise missiles. Carbon-graphite equipped cruise missileswere used by U.S.-led forces in raids on Baghdad, Iraq in1991 and in 2003.Scientists at Lawrence Livermore National Laboratoryreportedly developed an HPM weapon for the Departmentof Justice: aimed at a moving vehicle, the HPM couldshut off the electronic ignition, thus bringing a high-speedcar chase to an abrupt end.Encyclopedia of Espionage, Intelligence, and Security❚ FURTHER READING:BOOKS:“Electromagnetic Pulse Threats to U.S. Military and CivilianInfrastructure.” Hearing Before the Military Researchand Development Subcommittee of the Committee onArmed Services, U.S. House of Representatives, Oct. 7,1999 (H.A.S.C. No. 106–31). Washington, DC: U.S. GovernmentPrinting Office, 2000.PERIODICALS:Kruse, V. J., et al. “Impacts of a Nominal NuclearElectromagnetic Pulse on Electric Power Systems: AProbabilistic Approach.” IEEE Transactions on PowerDelivery. (Vol. 6, No. 3, July 1991): 1251–1263.SEE ALSONuclear Weapons❚ LARRY GILMANElectromagnetic SpectrumThe electromagnetic spectrum consists of all the frequenciesat which electromagnetic waves can occur, orderedfrom zero to infinity. Radio waves, visible light, and x raysare examples of electromagnetic waves at different frequencies.Every part of the electromagnetic spectrum isexploited for some form of military, security, or espionageactivity; the entire spectrum is also key to science andindustry.Basic PhysicsElectromagnetic waves have been known since the midnineteenthcentury, when their behavior was first describedby the equations of Scottish physicist James ClerkMaxwell (1831–1879). Electromagnetic waves, accordingto Maxwell’s equations, are generated whenever an electricalcharge (e.g., an electron) is accelerated, that is,changes its direction of motion, its speed, or both. Anelectromagnetic wave is so named because it consists ofan electric and a magnetic field propagating togetherthrough space. As the electric field varies with time, itrenews the magnetic field; as the magnetic field varies, itrenews the electric field. The two components of thewave, which always point at right angles both to eachother and to their direction of motion, are thus mutuallysustaining, and form a wave which moves forward throughempty space indefinitely.The rate at which energy is periodically exchangedbetween the electric and magnetic components of a givenelectromagnetic wave is the frequency, ν, of that wave and381