A system for measurement of harvested agricultural material in a cleaning assembly of a combine or harvester, the system comprising: a sieve (144, 158) of the cleaning assembly for separating the harvested agricultural material into crop residue and target crop material, characterized in that the system further comprises: at least one transmitter (54, 55, 56, 57) for generating or transmitting an electromagnetic signal; a set of transducers (20, 22, 24, 26) for converting the transmitted electromagnetic signal into transmitted waves within a target wavelength range comprising an ultrasonic wavelength range; a set of microphones (12, 14, 16, 18) for converting the transmitted waves into a received electromagnetic signal, each of the set of microphones (12, 14, 16, 18) longitudinally spaced apart from each other along a longitudinal axis of the sieve (144, 158) for reception of the transmitted electromagnetic signal in a first mode through the harvested agricultural material, or in a second mode reflected from the harvested agricultural material; a plurality of receivers for receiving the received electromagnetic signals associated with respective ones of the microphones (12, 14, 16, 18), each of the plurality of receivers arranged to detect a corresponding observed phase shift, observed attenuation or other observed signal parameters for its respective microphone; an electronic data processor for estimating a distribution or quantity of material on the sieve (144, 158) along the longitudinal axis based on the observed phase shift, the observed attenuation or the other observed signal parameters relative to a reference phase shift, a reference attenuation or other reference signal parameter associated with a corresponding reference distribution, volume, mass or quantity of material on the sieve (144, 158). at least one transmitter (54, 55, 56, 57) for generating or transmitting an electromagnetic signal; a set of transducers (20, 22, 24, 26) for converting the transmitted electromagnetic signal into transmitted waves within a target wavelength range comprising an ultrasonic wavelength range; a set of microphones (12, 14, 16, 18) for converting the transmitted waves into a received electromagnetic signal, each of the set of microphones (12, 14, 16, 18) longitudinally spaced apart from each other along a longitudinal axis of the sieve (144, 158) for reception of the transmitted electromagnetic signal in a first mode through the harvested agricultural material, or in a second mode reflected from the harvested agricultural material; a plurality of receivers for receiving the received electromagnetic signals associated with respective ones of the microphones (12, 14, 16, 18), each of the plurality of receivers arranged to detect a corresponding observed phase shift, observed attenuation or other observed signal parameters for its respective microphone; an electronic data processor for estimating a distribution or quantity of material on the sieve (144, 158) along the longitudinal axis based on the observed phase shift, the observed attenuation or the other observed signal parameters relative to a reference phase shift, a reference attenuation or other reference signal parameter associated with a corresponding reference distribution, volume, mass or quantity of material on the sieve (144, 158).