What does primary surveillance radar (PSR) rely on for its operation?

Primary surveillance radar (PSR) operates by using reflected radio waves to detect and determine the position of aircraft. It emits a radio signal that travels through the air, and when this signal encounters an object, such as an airplane, it reflects back to the radar system. The radar is designed to analyze the time it takes for the signal to return and the frequency change of the reflected waves, which helps in calculating the range, speed, and direction of the aircraft.

This method of operation is fundamental to PSR as it does not rely on the aircraft to send any information; rather, it passively detects the reflections from the aircraft. This is distinct from other systems like secondary surveillance radar (SSR), which does rely on interrogation-reply systems where the aircraft must actively respond to radar queries.

In summary, PSR's reliance on the natural reflection of radio waves is crucial for air traffic control and monitoring, as it allows for a continuous and wide-area monitoring capability without needing onboard transponders from the aircraft.