Perimeter surveillance radar

Perimeter surveillance radar (PSR) is a class of radar sensors that monitor activity surrounding or on critical infrastructure areas such as airports, seaports, military installations, national borders, refineries and other critical industry and the like. Such radars are characterized by their ability to detect movement at ground level of targets such as an individual walking or crawling towards a facility.

Source: Wikipedia — Perimeter surveillance radar (CC BY-SA 4.0)