A system comprising: a dissolving tank (160, 260) adjacent to a recovery boiler, a smelt spout having a first end proximate a recovery boiler and a second end opposite the first end, the second end being proximate a dissolving tank (160, 260), wherein the smelt spout is configured to receive a smelt from the recovery boiler and convey the smelt to the dissolving tank (160, 260); an acoustic emission sensor (150, 250) having a reading end configured to detect acoustic emissions (167, 376) emanating from the smelt contacting a liquid in the dissolving tank (160, 260), and wherein the acoustic emission sensor (150, 250) has a transducer (285, 385) in signal communication with the reading end, and wherein the transducer (285, 385) is configured to transduce the acoustic emissions (167, 376) into an initial electric signal; a pre-processor configured amplify, filter, and digitize the initial electric signal to produce a pre-processed signal having a frequency of greater than 20 KHz, wherein the pre processor is disposed downstream of the transducer (285, 385); a data processor in signal communication with the pre-processor, wherein the data processor is configured to transform the pre-processed signal with a transformation method to produce an output signal, wherein the output signal comprises a first set of processed waveforms (432, 532) representative of a first rate of smelt flow, and a second set of waveforms (433, 533) representative of a second rate of smelt flow, the second set of processed waveforms (433, 533) having amplitude peaks (461, 561) exceeding the first set of processed waveforms (432, 532) by more than 200% to comprise a pre-influx fingerprint. a dissolving tank (160, 260) adjacent to a recovery boiler, a smelt spout having a first end proximate a recovery boiler and a second end opposite the first end, the second end being proximate a dissolving tank (160, 260), wherein the smelt spout is configured to receive a smelt from the recovery boiler and convey the smelt to the dissolving tank (160, 260); an acoustic emission sensor (150, 250) having a reading end configured to detect acoustic emissions (167, 376) emanating from the smelt contacting a liquid in the dissolving tank (160, 260), and wherein the acoustic emission sensor (150, 250) has a transducer (285, 385) in signal communication with the reading end, and wherein the transducer (285, 385) is configured to transduce the acoustic emissions (167, 376) into an initial electric signal; a pre-processor configured amplify, filter, and digitize the initial electric signal to produce a pre-processed signal having a frequency of greater than 20 KHz, wherein the pre processor is disposed downstream of the transducer (285, 385); a data processor in signal communication with the pre-processor, wherein the data processor is configured to transform the pre-processed signal with a transformation method to produce an output signal, wherein the output signal comprises a first set of processed waveforms (432, 532) representative of a first rate of smelt flow, and a second set of waveforms (433, 533) representative of a second rate of smelt flow, the second set of processed waveforms (433, 533) having amplitude peaks (461, 561) exceeding the first set of processed waveforms (432, 532) by more than 200% to comprise a pre-influx fingerprint.