Signals Intelligence (SIGINT) is one of the oldest missions for satellites, especially for its subfield, Electronic Intelligence (ELINT), the analysis and localization of collection of radio frequency (RF) signals.
SIGINT makes it possible to analyze the electromagnetic spectrum, detect interference and transmissions by unauthorized third parties, and identify signals from Earth and outer space. The ability to locate sources of interference is increasing interest in telecommunications industry. Its applications include national security duties and vessel tracking.
Small satellites (nanosatellites and microsatellites under CubeSat standard) can monitor radio signals, so in the event of a disaster, they can provide information regarding the degree of impact and the most seriously affected areas, allowing for more effective planning of rescue.
The main driver for moving towards small satellite constellations is the ability to dramatically lower the cost of old space or airborne missions. In the civilian domain this means essentially opening a new type of business, in the security domain it means lowering the cost of entry for countries seeking to acquiring Spectrum Monitoring capabilities.