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Multifrequency analyses of 2011-2012 Peace River SWIPS frazil backscattering data

机译：2011-2012年和平河SWIPS巴西反向散射数据的多频分析

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摘要

A four-frequency SWIPS (Shallow Water Ice Profiling Sonar) instrument was deployed in the Peace River during the November 2011 -May 2012 period near the Town of Peace River. The deployment site was previously used for deployments of one- and two-frequency SWIPS instruments. Acoustic volume backscattering coefficient and ice thickness data were collected at frequencies 125 kHz, 235 kHz, 455 kHz and 774 kHz. The data, acquired as a function of height in the water column, were processed to test particle size, concentration and acoustic frequency restrictions identified in a closely-related laboratory study of backscattering in pseudo-frazil suspensions (Marko & Topham, 2015) prior to applying optimal processing strategies on the 2011-2012 frazil data. Although one of the transducers (235 kHz) displayed anomalous returns under certain environmental conditions, simultaneous measurements at 125 kHz, 455 kHz and 774 kHz were found to yield consistent measures of particle concentration, size distribution and fractional volume with accuracies limited, primarily, only by the 1 dB transducer calibration uncertainties. Fractional volumes were found to vary by less than an order of magnitude from interval to interval, with maximum values being approximately 10~(-4) (0.01%) except within, roughly, 0.75 m of the river surface where interpretations were complicated by the frequent presence of surface ice. These results confirmed the effectiveness of multifrequency acoustic backscattering sonar (ABS) technology in applications to frazil monitoring problems and expanded its range of applicability beyond that conservatively estimated in the laboratory. The obtained data also provided an unprecedented basis for evaluating current river ice modeling assumptions. Comparisons with corresponding results from CRISSP model runs appear to be indicative of massive over-prediction of suspended frazil despite good model performance for simulating surface ice quantities. The origins of the possible discrepancies are discussed and accompanied by suggested options for improving model performance.
机译：在和平河附近的2011年11月至2012年5月期间，在和平河中部署了四频SWIPS（浅水冰剖析声纳）仪器。部署站点以前曾用于一频率和二频率SWIPS仪器的部署。在125 kHz，235 kHz，455 kHz和774 kHz的频率下收集了声学体积反向散射系数和冰厚数据。将数据作为水柱高度的函数进行处理，以测试在伪巴西悬浮液的反向散射的密切相关实验室研究中发现的粒径，浓度和声频限制（Marko＆Topham，2015）。对2011-2012年的巴西数据应用最佳处理策略。尽管其中一个换能器（235 kHz）在某些环境条件下显示出异常的返回值，但是发现在125 kHz，455 kHz和774 kHz的同时测量可以对颗粒浓度，尺寸分布和分数体积进行一致的测量，而精度有限，主要是，通过1 dB的传感器校准不确定性。研究发现，每个区间的分数体积变化幅度小于一个数量级，最大值大约为10〜（-4）（0.01％），除了大约0.75 m的河面以内，解释复杂。经常存在地表冰。这些结果证实了多频声背向散射声纳（ABS）技术在解决巴西监测问题中的有效性，并将其适用范围扩展到了实验室保守估计的范围之外。获得的数据也为评估当前河冰模型假设提供了前所未有的基础。与CRISSP模型运行的相应结果进行的比较似乎表明，尽管模拟表面冰量具有良好的模型性能，但对悬浮的巴西腈的预测过高。讨论了可能出现差异的原因，并提出了改善模型性能的建议选项。

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