A combine harvester including an aft portion, a spreader assembly, a monitoring system, and a processing unit. The monitoring system including sensors coupled to the aft portion. The sensors: receiving a plurality of response waves reflected from a portion of the crop residue that is discharged from the spreader assembly toward a discharge area before the portion of crop residue arrives at the discharge area; and sending a response signal representative of the plurality of response waves reflected from the portion of the crop residue, the reflected waves comprising a sequence of multiple reflections distributed over time. The processing unit receiving the response signal from the plurality of sensors; and processing the response signal to determine a reflected energy distribution from the portion of the crop residue representative of a distribution of the crop residue over the discharge area substantially perpendicular to a travel direction of the combine harvester.