A sensor for monitoring a plant population in front of a harvester and a transfer process of the crop from the harvester to a transport vehicle is arranged on an unmanned aircraft. The aircraft moves in the vicinity of the harvester in the harvesting mode and communicates in a wireless fashion with a control unit that controls an actuator for influencing an operating parameter of the harvester and/or the transport vehicle (in real time based on signals of the sensor in the harvesting mode.