Smart Micro Radar Altimeter Video: 
Radar Altimeter Terrain Flight

Radar altimeter reliably determines the current altitude and vertical speed over all kind of surfaces. 
Being light weight (now new 160g version available), precise, robust, weather- and sunlight- independent they are ideal for many types of aircraft: small airplanes, helicopters, unmanned aerial vehicles (UAV) or MAV. Low power consumption makes them perfect for battery powered applications. Having a wide beam antenna the radar altimeters are able to operate under pitch and roll angles of up to 20 degree.