Final answer:
Radar clutter occurs when the radar screen is covered with dots from aircraft transponders responding to other ground-based interrogators. Air traffic controllers use various techniques to mitigate radar clutter.
Step-by-step explanation:
When the controller's PPT, or radar screen, becomes covered with small random dots from aircraft transponders responding to other ground-based interrogators, it is known as radar clutter.
Radar clutter occurs when the radar system detects unwanted echoes or signals that interfere with the desired radar return. In this case, the small random dots represent the aircraft transponders responding to other ground-based interrogators, creating clutter on the radar screen.
To mitigate radar clutter, air traffic controllers use different techniques such as adjusting the radar gain, antenna rotation, or using clutter suppression algorithms to enhance the signal-to-noise ratio and distinguish the desired targets from clutter.