Signals intelligence
Also called: SIGINT, COMINT · Topic: Remote Sensing, GIS and GNSS · NCERT: Beyond NCERT
Meaning
Signals intelligence (SIGINT) is information gathered by catching and studying electronic signals sent out by others. It has two main branches. Communications intelligence (COMINT) comes from messages, such as radio talk or phone calls. Electronic intelligence (ELINT) comes from signals that carry no message, such as radar pulses, so it is used to locate an enemy's radars and air-defence systems. Satellites in orbit can listen across a wide area and a broad range of frequencies, so SIGINT is an important part of national security.
Example
India's EMISAT, built by DRDO, is an ELINT satellite. It was launched on PSLV-C45 on 1 April 2019 from Sriharikota, Andhra Pradesh, into a sun-synchronous polar orbit about 748 km high. Its job is to measure the electromagnetic spectrum, which means recording radio and radar signals from the ground.
Don't confuse with
- COMINT vs ELINT: both are types of SIGINT, not other names for it. COMINT listens to messages between people. ELINT studies non-message signals such as radar.
- Remote sensing (imagery intelligence): remote sensing makes pictures of the earth from reflected or emitted energy. A radar satellite like RISAT does this by sending out its own pulses. SIGINT makes no images. It only picks up signals that other systems send out.