Abstract: A sensor system for defending armoured vehicles against projectiles through the use of active armour. A thermal sensor detects a projectile's presence, and a laser proximity sensor determines its location. A doppler sensor distinguishes between threatening and nonthreatening projectiles by measuring the projectile's velocity. The sensors are positioned in a housing with a segmented spherical window, wherein each sensor can detect the projectile through a window segment having a filtering characteristic which is matched to its associated sensor. An eyelid shutter, which can open and close, protects the window from small arms fire and shrapnel. A conical deflector protects the sensor system from objects such as tree branches. Heater elements are used to clear ice and snow from the window, and the eyelid shutter removes other material through the use of a cleaning liquid delivery system and rubber wipers.