Abstract: A method of and control system for controlling transport of fibrous material travelling in dune or dune and layer flow mode conveyed by a pneumatic fluid flow through a transport line of a pneumatic conveying system, such as a cut tobacco conveying system in a device for feeding cut tobacco to a tobacco processing device. The transport velocity of a dune or layer and the velocity of pneumatic fluid passing the dune or layer in the transport line are determined. A difference between the determined dune or layer transport velocity and the determined passing fluid velocity is controlled by controlling the pneumatic fluid flow in the transport line. An optical sensor and a computer program product for use with the method and system are provided.