Frazil ice measurements using the four-frequency AQUAscat sonar in laboratory and field environments

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Shoorangiz, Leila
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This research describes laboratory experiments conducted to investigate the capability of a multifrequency Aquatec AQUAscat 1000R sonar in detecting and measuring frazil ice particles. A series of laboratory experiments were conducted at the University of Manitoba and the University of Alberta to measure the particle size and concentration of frazil ice particles using four transducers, including 0.3, 0.5, 2 and 4 MHz. Also, the AQUAscat Toolkit software was utilized to post-process the logged data using the sonar instrument. The results indicated that the 2 MHz transducer was the most sensitive to the presence of frazil ice particles, while the 0.3 MHz had the least sensitivity. The device started to detect the frazil ice particles when the maximum supercooling occurred. The concentration was determined to reach its maximum value of 0.65% and 0.45% in different setups at the University of Manitoba and the University of Alberta, respectively. The outcomes showed that the mean frazil particle size ranged from 100 to 300 µm at the University of Alberta in a supercooling event. In contrast, the findings based on experiments conducted at the University of Manitoba were unreliable due to the large number of bad cells within the particle size data. The multifrequency sonar instrument was deployed on the riverbed at Dauphin River for a one-day experiment on December 6, 2022. It was revealed that the apparatus was able to detect the frazil ice particles but not the frazil flocs and ice rafts. The results showed that the average concentration of frazil ice was 0.0066%. Although the particle size outcomes were not reliable in the first 25 cm above the transducers, the average particle size in the rest of the water column was found to be between 150 and 300 µm.
multifrequency sonar instrument, frazil ice, supercooling event, river ice