Radar, electromagnetic sensor used for detecting, locating, tracking, and recognizing objects of various kinds at considerable distances. It operates by transmitting electromagnetic energy toward objects, commonly referred to as targets, and observing the echoes returned from them. Option 1 is not correct: At the airports scanners use X- ray machines and metal detectors and not radar-based detectors (which use long-wave radiations; radiowaves) are generally used. At the same time, millimetre wave radar applications have also been used for airport surface movement control and foreign object detection, but the same cannot be called conventional radar. Thus option 1 is not correct. Option 2 is correct: Weather radars can be used to monitor the weather of a particular place. Option 3 is correct: Using radar has allowed researchers to examine migration altitude, speed, and wing beat frequency of birds, bats, and even insects during migration.