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年冬季使用聲學浮游動物魚剖面儀的見解--加拿大紐芬蘭與拉布拉多努納特西瓦特地區沿海水域的冰層情況

Index Terms—sonar, underwater acoustics, instrumentation,ice characteristics, plankton

關鍵詞：聲納，水下聲學，儀器設備，冰的特性，浮游生物

摘要——為了支持通過加拿大沿海地區由原住民主導的倡議所追求的海洋管理和海洋保護目標，需要更好地理解海洋在調節氣候和維持復雜食物網方面的作用。拉布拉多海努納茨亞武特的傳統領海擁有豐富多樣的海洋生態系統，該系統受物理海洋學和季節性海冰覆蓋的綜合影響，并由風和洋流向南輸送。努納茨亞武特政府開展了一項不斷擴大的研究項目，以了解和監測這個復雜的生物物理系統，以支持有效的環境管理。作為該研究項目的一部分，他們目前正處于對拉布拉多奈恩附近一個近海站點的冬季海洋和海冰狀況進行監測的第五年。在這個站點進行的測量包括水溫、鹽度、溶解氧、濁度、洋流以及冰的吃水深度和速度。將這些測量結果結合起來，以了解海洋在調節氣候和復雜食物網中的作用，是支持由原住民主導的研究倡議和加拿大沿海地區海洋管理的重要一步。

努納茨亞武特政府與ASL環境科學公司合作，通過支持首次部署名為AZFP - ice的新型ASL儀器，進一步開展該站點的環境監測。AZFP - ice旨在從其校準后的（±1 dB）多頻聲學傳感器收集高時間和空間分辨率的冰吃水深度測量數據以及同步的生物觀測數據。AZFP - ice是一種經過校準的科學單波束回聲測深儀。AZFP - ice使用中心頻率為417 kHz的窄波束通道來獲取冰龍骨深度，類似于ASL的冰剖面聲納（IPS）。同步生物觀測通過三個獨立通道實現，在中心頻率為125 kHz、200 kHz和769 kHz時收集校準后的反向散射測量數據。

基于ASL在聲學浮游動物魚類剖面儀（AZFP）聲納系統方面的經驗，AZFP - ice設計為每次可自主運行長達12個月。AZFP - ice還配備了升級的電子設備包，允許在內部存儲多達1 TB的數據。其續航能力和內部存儲容量使其具有出色的時間覆蓋范圍，并且使該儀器非常適合在具有挑戰性的環境中部署。（異地）工廠校準允許在絕對尺度上測量反向散射，這便于進行下游處理，例如漁業聲學中常見的所謂“dB差分”方法。

本文介紹了新型AZFP - ice，并展示了其作為環境監測工具的能力。在AZFP - ice附近放置了一臺IPS - 5，以便比較觀測到的冰特征。對2021年至2022年冬季部署期間收集的數據進行的初步分析表明，AZFP - ice有助于海冰特征描述。冬季的大部分時間里，固定冰占主導，通過間距很近的AZFP - ice和IPS - 5對從解體到冰清除的不同冰段進行了比較。

在固定冰期，冰的動態變化較為簡單，因為冰對熱力強迫做出響應。冬季白晝時間大幅減少，但與高緯度環境不同，這個環境不會出現24小時黑暗。雖然冰可能靜止不動，但AZFP - ice的其他頻率表明，在白晝減少的這段時間里，冰下活動仍在繼續。在本文中，我們回顧了這次部署的實例，展示并討論了AZFP - ice對冰下生物的聲學觀測。結果表明，AZFP - ice在一臺儀器中提供了獨特的測量組合，為研究人員提供了物理背景（即冰厚度）以及生物數據。 

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.