Before you can take anything out, you have to detect it. Counter-UAS (C-UAS) is therefore always detect + defeat, and detection combines several sensors because every individual method has weak spots:
- RF detection: passively listening in on the control and video link. Often the first indication — and it can also give away the operator's position (compare ESM, EW: Electronic Support Measures).
- Radar: recognising small, slow targets, among other things through the micro-Doppler of rotating rotor blades (Radar) — a characteristic signature that distinguishes a drone from a bird.
- EO/IR: visual and infrared recognition (Infrared) at shorter range, also for identification.
- Acoustics: the characteristic buzz — limited range, but it also works against drones that emit no RF (see fibre-optic, Lessons from Ukraine (open source)).