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6.72 Radar Procedures
6.72.2 State the two types of radar currently used in New Zealand.
New Zealand has near-complete coverage from both primary and secondary radar.
6.72.4 Describe the method of operation of each type of radar
Primary Radar
Operates on the echo principle: signals transmitted from a ground-based aerial strike an aircraft and scatter in all directions. A portion of this energy is reflected back to the radar aerial. The time taken for the signal to travel to the aircraft and return is used to determine the aircraft’s distance.
Secondary Radar
Operates differently to Primary radar. A signal transmitted from the ground-based aerial is received by the aircraft’s transponder (interrogation), which immediately sends a reply back to the radar station. The time between transmission of the interrogation signal and reception of the reply is used to determine the aircraft’s distance.
Radar systems operate on VHF or UHF frequencies. These frequencies rely on line-of-sight, meaning terrain such as mountains can block the signal. As a result, aircraft flying at lower altitudes may not be detected, while higher altitudes improve radar coverage.