Which of the following would not be a passive form of Target Surveillance and Identification?

Identification Friend or Foe (IFF) is a system that allows for the identification of an aircraft or vehicle as friendly or enemy. Unlike passive surveillance methods, which do not emit signals and rely on detecting signals from other sources, IFF actively sends out interrogating signals that require a responding signal from the target. This interaction defines it as an active system rather than passive surveillance.

In contrast, visual surveillance, electronic warfare support, and electro-optics/infrared methods do not emit signals but rely on observing, detecting, or analyzing the electromagnetic spectrum to gather information about targets without revealing their own position. This characteristic is fundamental to passive surveillance techniques, as they aim to minimize detection and avoid being countered or targeted.