The discipline of studying wireless traffic to establish patterns and obtain intelligence, a component of signals analysis and signals intelligence. Traffic analysis includes techniques of direction-finding, call-sign analysis, and discrimination—the study of frequencies, wavelengths, and transmission lengths.
Even without being able to solve cryptographically a ciphered text, a skilled analyst may develop significant information about a particular source of radio broadcasts by monitoring the regularity of the signals, their length, frequency, call sign, and origin. For example, the sudden imposition of radio silence may indicate an imminent attack, and the movement of a particular operator may indicate a change in location for his unit.
Perhaps the most significant moment in the history of traffic analysis occurred in 1938 at the end of the Munich Crisis when the German battleship Deutschland, on a goodwill visit to Spain, continued its cruise with a crew of cadets and did not return to her home port.
British direction-finding confirmed the ship’s position, thereby confirming that war was not imminent.