For ascents of model aircraft / drones and unmanned aerial systems, depending on the place of ascent, an air traffic control clearance must be obtained from the responsible air traffic control center in accordance with §21 LuftVO.
Information from the Ministry of Environment, Climate, Mobility, Agriculture and Consumer Protection on this topic can be found here.
Ministry of the Environment, Climate, Mobility, Agriculture and Consumer Protection Division F/2 - Aviation Keplerstrasse 18 66117 Saarbrücken