What type of system does secondary surveillance radar (SSR) use?

Secondary Surveillance Radar (SSR) utilizes an interrogation-reply system. This technology functions by sending out a radio frequency signal from the ground station to an aircraft's transponder. The transponder then responds by transmitting a signal back to the ground station, effectively providing information such as the aircraft's identity and altitude.

This relationship is crucial for air traffic control, as it allows for more precise tracking of aircraft compared to primary radar systems, which only reflect signals off the aircraft without receiving additional information. By relying on the interrogation-reply method, SSR enhances situational awareness and helps avoid ambiguity in identifying multiple aircraft in the same airspace.

Thus, the interrogation-reply nature of SSR is integral to its operation, making it a vital component in modern aviation surveillance and coordination.