The technology of the invention relates to an ultrasonic characterization method for a flowstream to detect impurities that can include placing a first transducer and a second transducer aligned confocally to a flowstream, transmitting, from the first transducer, ultrasonic waveform signals into the flowstream, receiving, by the second transducer, the ultrasonic waveform signals, removing waveform signal reflections using a pitch-catch configuration of the first transducer and the second transducer, detecting waveform signals indicating impurities in the flowstream using induced nucleation of the impurities, detecting waveform signals indicating bubbles in the flowstream using nonlinear dynamic behaviors of the bubbles, and differentiating between the waveform signals of the impurities and the waveform signals of the bubbles using cavitation properties of the impurities and the bubbles.