What type of scanning indicator do surveillance radars primarily use?

Surveillance radars primarily use a plan-position indicator (PPI) because this type of display provides a comprehensive view of the radar environment. The PPI presents data in a two-dimensional format where the radar antenna is at the center of the display, and the surrounding area is shown in a circular manner. This allows operators to easily identify the position and movement of targets relative to the radar's location.

The PPI is particularly effective for air traffic control and military applications because it simplifies the process of interpreting target data. Operators can quickly gauge the distance, bearing, and direction of targets, facilitating situational awareness and decision-making. The visual representation on the PPI screen makes it intuitive for users to monitor multiple targets simultaneously.

Other display types, like a vertical scan electron beam display, do not offer the same level of situational awareness as PPI, as they typically focus on a single vertical slice of the environment rather than a comprehensive view. This makes them less effective for the wide-ranging monitoring required in surveillance contexts.