Signals intelligence is derived from signal intercepts comprising, either individually or in combination, all communications intelligence (COMINT), electronic intelligence (ELINT), and foreign instrumentation signals intelligence (FISINT), however, transmitted. COMINT, one of the primary SIGINT disciplines, includes information derived from intercepted communications transmissions.
COMINT targets voice and teleprinter traffic, video, Morse code traffic, or even facsimile messages. Assuming access is possible, COMINT can be collected from the airwaves, cable, fiber optics, or any other transmission medium.
ELINT includes the interception and analysis of non-communications transmissions, such as radar. ELINT is used to identify the location of an emitter, determine its characteristics, and infer the characteristics of supported systems.
FISINT consists of intercepts of telemetry from an opponent’s weapons systems as they are being tested. Telemetry units provide designers with information on a prototype’s guidance system operation, fuel usage, staging, and other parameters vital for understanding operational characteristics. These data enable the designer to evaluate the performance of the prototype. However, if intercepted, they also provide an adversary with the ability to estimate the capability of the prototype.
Signals intelligence collection can be performed from a variety of platforms. Examples include overt ground collection sites, such as the Russian facility at Lourdes, Cuba; ships and aircraft. SIGINT facilities can monitor transmissions from communications satellites, as well as terrestrial facilities. International communications satellites are routinely monitored by foreign intelligence services. The majority of collection capabilities targeting a powerful country may be ground or sea-based, and target line of site or satellite communication systems.