Which of the following is NOT a type of Missile Approach Warning System (MAWS)?

A Missile Approach Warning System (MAWS) is designed to detect incoming missile threats using various sensor technologies. One commonly used type of sensor is ultraviolet, which detects the heat signatures emitted by missile exhaust. Infrared systems also specialize in detecting heat and are particularly effective against thermal targets, such as missile launches. RADAR systems can track the trajectory and motion of objects in the air, including missiles, providing critical information about incoming threats.

Acoustic detection, while useful in certain contexts, is not typically associated with missile approach warning systems. Acoustic sensors function by detecting sound waves and are more suited to underwater or surface applications rather than detecting airborne threats like missiles. Therefore, the selection of acoustic as the answer correctly identifies it as not being a type of MAWS used to warn against missile approaches.