In the language of specialists, very low flight is known as hedge-hopping or skimming. In this mode, the missiles fly at very low altitude (100 m and less) completely independently in order to avoid detection by enemy defences. This type of navigation of cruise missiles has been under study at ONERA for several years.

To be able to remain in the programmed flight corridor and follow the relief as closely as possible, missiles of this type have an inertial measurement unit and auxiliary sensors such as radar, radioaltimeter and GPS receiver. A computer whose memory contains the geographic area overflown manages the overall consistency.

And This is Important Too :

Because of its experience, specifically in navigation for Stand-Off weapon systems, ONERA is expert to the DGA APACHE/SCALP team for the development of these French cruise missile programmes. APACHE is a Matra-Aerospatiale missile, and SCALP is a Matra BAe Dynamics missile. DGA is the french arms-procurement agency, part of defence ministry.