Insights from Winter 2021-22 using an Acoustic Zooplankton Fish Profiler - Ice in the Coastal Waters of the Nunatsiavut Region of Newfoundland and Labrador, Canada
2021-22年冬季使用声学浮游动物鱼剖面仪的见解--加拿大纽芬兰与拉布拉多努纳特西瓦特地区沿海水域的冰层情况
Index Terms—sonar, underwater acoustics, instrumentation,ice characteristics, plankton
关键词：声纳，水下声学，仪器设备，冰的特性，浮游生物
摘要——为了支持通过加拿大沿海地区由原住民主导的倡议所追求的海洋管理和海洋保护目标，需要更好地理解海洋在调节气候和维持复杂食物网方面的作用。拉布拉多海努纳茨亚武特的传统领海拥有丰富多样的海洋生态系统，该系统受物理海洋学和季节性海冰覆盖的综合影响，并由风和洋流向南输送。努纳茨亚武特政府开展了一项不断扩大的研究项目，以了解和监测这个复杂的生物物理系统，以支持有效的环境管理。作为该研究项目的一部分，他们目前正处于对拉布拉多奈恩附近一个近海站点的冬季海洋和海冰状况进行监测的第五年。在这个站点进行的测量包括水温、盐度、溶解氧、浊度、洋流以及冰的吃水深度和速度。将这些测量结果结合起来，以了解海洋在调节气候和复杂食物网中的作用，是支持由原住民主导的研究倡议和加拿大沿海地区海洋管理的重要一步。
努纳茨亚武特政府与ASL环境科学公司合作，通过支持首次部署名为AZFP - ice的新型ASL仪器，进一步开展该站点的环境监测。AZFP - ice旨在从其校准后的（±1 dB）多频声学传感器收集高时间和空间分辨率的冰吃水深度测量数据以及同步的生物观测数据。AZFP - ice是一种经过校准的科学单波束回声测深仪。AZFP - ice使用中心频率为417 kHz的窄波束通道来获取冰龙骨深度，类似于ASL的冰剖面声纳（IPS）。同步生物观测通过三个独立通道实现，在中心频率为125 kHz、200 kHz和769 kHz时收集校准后的反向散射测量数据。
基于ASL在声学浮游动物鱼类剖面仪（AZFP）声纳系统方面的经验，AZFP - ice设计为每次可自主运行长达12个月。AZFP - ice还配备了升级的电子设备包，允许在内部存储多达1 TB的数据。其续航能力和内部存储容量使其具有出色的时间覆盖范围，并且使该仪器非常适合在具有挑战性的环境中部署。（异地）工厂校准允许在绝对尺度上测量反向散射，这便于进行下游处理，例如渔业声学中常见的所谓“dB差分”方法。
本文介绍了新型AZFP - ice，并展示了其作为环境监测工具的能力。在AZFP - ice附近放置了一台IPS - 5，以便比较观测到的冰特征。对2021年至2022年冬季部署期间收集的数据进行的初步分析表明，AZFP - ice有助于海冰特征描述。冬季的大部分时间里，固定冰占主导，通过间距很近的AZFP - ice和IPS - 5对从解体到冰清除的不同冰段进行了比较。
在固定冰期，冰的动态变化较为简单，因为冰对热力强迫做出响应。冬季白昼时间大幅减少，但与高纬度环境不同，这个环境不会出现24小时黑暗。虽然冰可能静止不动，但AZFP - ice的其他频率表明，在白昼减少的这段时间里，冰下活动仍在继续。在本文中，我们回顾了这次部署的实例，展示并讨论了AZFP - ice对冰下生物的声学观测。结果表明，AZFP - ice在一台仪器中提供了独特的测量组合，为研究人员提供了物理背景（即冰厚度）以及生物数据。
Abstract—Improved understanding of the role of the ocean in moderating climate and sustaining complex food webs is required to support ocean stewardship and ocean protection goals being pursued through Indigenous-led initiatives across Canada’s coastlines. The traditional territorial waters of the Nunatsiavut in the Labrador Sea contain a rich and diverse marine ecosystem
regulated by a combination of physical oceanography and the presence of seasonal sea ice cover, transported southward by wind and ocean currents. The Nunatsiavut Government operates a growing research program to understand and monitor this complex biophysical system to support effective environmental management. As part of this research program, they are now in the fifth year of monitoring over-winter ocean and sea ice conditions at an offshore site near Nain, Labrador. Measurements made at this site have included water temperature, salinity, dissolved oxygen, turbidity, currents, and ice drafts and velocities.
Combining these measurements to understand the ocean’s role in moderating climate and complex food webs is an important step in support of Indigenous-led research initiatives and ocean stewardship across Canada’s coastlines.
The Nunatsiavut Government has collaborated with ASL Environmental Sciences to further develop environmental mon- itoring at this site by supporting the first-ever deployment of the new ASL instrument known as the AZFP-ice. The AZFP-ice is designed to collect high temporal and spatial resolution measurements of ice draft and simultaneous biological obser-vations from its calibrated (±1 dB) multifrequency acoustical sensors. The AZFP-ice is a calibrated, scientific, singlebeam echosounder. The AZFP-ice uses a narrow beam 417 kHz center frequency channel to obtain ice keel depth, similar to ASL’s Ice Profiling Sonar (IPS). Simultaneous biological observations are realized using three separate channels, collecting calibrated backscatter measurements at 125 kHz, 200 kHz, and 769 kHz center frequencies.
Building on ASL’s experience with the Acoustic Zooplankton Fish Profiler (AZFP) sonar system, the AZFP-ice is designed to operate autonomously for up to 12 months at a time. The AZFP-ice also features an upgraded electronics package that allows up to 1 TB of data to be stored internally. Its endurance and its internal memory capacity allow for excellent temporal coverage and make the instrument well-suited for deployment in challenging environments. The (ex situ) factory calibration allows backscatter to be measured on an absolute scale, which facilitates downstream processing such as the so-called ‘dB differencing’ approach that is common in fisheries acoustics.
This paper introduces the new AZFP-ice and showcases its capabilities as a tool for environmental monitoring. An IPS-5 was located near the AZFP-ice, allowing for a comparison of the observed ice characteristics. Preliminary analysis of the data collected during an over-winter deployment from 2021 to 2022 indicates that the AZFP-ice facilitates sea-ice characterization.
Much of the over-winter period is dominated by landfast ice, and segments of ice from break-up to ice clearing are compared from the closely spaced AZFP-ice and IPS-5.During the period of landfast ice, the ice dynamics are simple as the ice responds to the thermodynamic forcing. Daylight hours are greatly reduced in the winter, but this environment does not experience 24-hour darkness, unlike high-latitude environments. While the ice may be motionless, the other AZFP-ice frequencies indicate that below the ice activity continues during this period of reduced daylight. In this paper, the AZFP-ice’s acoustical observations of the under-ice biology are presented and discussed as we review examples from this deployment. The AZFP-ice is shown to provide a unique combination of measurements in a single instrument, offering researchers a physical context (i.e. ice thickness) alongside biological data.
