Abstract: A monitoring system for a combine harvester having a header for harvesting a crop and a residue spreading system for spreading a crop residue. The monitoring system includes a sensing system configured to provide one or more measurement waves that intersect a flow of crop residue discharged by the spreading system and receive a plurality of response waves reflected from the crop residue. The system further includes a processing unit configured to receive a response signal of the sensing system; process the response signal; and determine, based on the response signal, a density and velocity distribution of the crop residue across a two-dimensional measurement area. The response signal is representative of the plurality of response waves reflected from the crop residue. The measurement area is at an end of a trajectory of the crop residue towards a deposit area.