Inspecting an F-16 electronic countermeasures pod Electronic countermeasures or ECM are any sort of electrical or electronic device designed entirely to "spoof" radar, sonar, or other detection systems. They may be used both offensively or defensively in any method to deny targeting information to an enemy. The system may make there appear to be hundreds of separate targets, or make the real target appear to dissapear or move about randomly. It is used effectively to protect aircraft from guided missiles. Many Air Forces use them to protect their aircraft from attack.
Offensive ECM often takes the form of jamming. Defensive ECM includes using chaff against air stikes, as well as soids, blip enhancement and jamming of missile terminal homers.
ECM is practiced by nearly all military units -- land, sea or air. Aircraft are the primary weapons in the ECM battle because they can "see" a larger patch of earth than a sea or land based unit. When employed effectively, ECM can keep aircraft from being tracked by surface to air and air to air munitions.
ECM is a function of the electromagnetic spectrum or frequency of energy that is directed toward a target. Every type of RADAR functions in the electromagnetic spectrum and can be sensed by the proper equipment. Since RADAR works very much like an echo you hear if you yell into a chasm or canyon, it can be timed and identified by the frequency at which it operates. For example, if you strum an low "e" string on a guitar, it resonates at a frequency of 440 hz or hertz. Hertz is the unit in which frequency is measured, like "12" inches, it's "400" hertz. So you strum your guitar string, it resonates at 440 hz, and the sound waves travel out like ripples in a pond and in all directions. When the waves reach the other side of the canyon, they are reflected or bounced back toward the source. The sound arrives at your ear after a short time and you hear the "echo". If someone on he other side of the canyon has a guitar tuned to 442 hz and they strum it as soon as they hear the sound from your guitar, their sound will reach you at approximately the same time as your echo. This combination of sounds will sound strange to you. A RADAR system is much more accurate while it listens for the echo. If it sends out 440 hz, it expects to "hear" a reflected 440 hz. If the sound comes back at 442 or 445 hz, then the RADAR receiver or "ear" can be confused.
Although almost all radars transmit and receive in the Mhz or Ghz (Megahertz or Gigahertz) range of frequencies. These frequencies are far above the hearing ability of humans, but the energy sent and received works just like your guitar.
ECM is practiced and applied in simulators and training ranges located around the globe. These methods of training ensure that our pilots, seamen and land troops are familiar with enemy threats and are capable of jamming, covering or elimination. Many sophisticated methods of jamming an electromagnetic signal exist and descriptions of them may be added later. Covering involves overpowering a signal so that the RADAR receiver is overwhelmed and cannot process the echo. Elimination consists of missiles and bombs that home in on the RADAR signal and destory the source.
The US Air Force used the F-111 and the F-4 in Vietnam as RADAR busters. These "Wild Weasels" were armed with H.A.R.M. (High-speed Anti-Radiation Missile) munitions which followed a reverse path down the RADAR beam and blew up the source of the radiation. This was successful and many lives were saved using the "Wild Weasels".
Almost all modern ECM platforms rely on computers to interperet the incoming RADAR signal and select the best or most effective response to the received threat. The US Air Force bombers do not have the gunners of yesteryear and rely on sophisticated countermeasures to combat electronic threats and survive above today's battlefields.
Another kind of ECM is more offensive in theory. It involves using an electromagnetic pulse or EMP to overdrive or burn out all electronics. This can be very effective prior to an attack if you can knock out the enemy's ability to communicate quickly. It is obviously a very good psychological weapon as TVs, radios, computers and cell phones can be rendered useless at the touch of a button. Imagine ATM's, checkout scanners and digital gas pumps not working suddenly. It's a very effective weapon.
The US Air Force is currently testing an airborne laser which will be used to knock nuclear and conventional warheads out of the sky using light as a weapon. While this doesn't really follow the guidelines I laid out above, it can still be considered ECM as light falls into the electromagnetic spectrum.
For more information about the topics discussed here, go to http://www.af.mil/ and follow the links to areas of interest.
Examples of dedicated electronic countermeasures aircraft
See also
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