| 淡水水体气泡的声学信号特征与识别研究 ——以乐昌峡水库为例 |
| Acoustic Signal Features and Recognition of Bubbles in Fresh Water: A Case Study in Lechangxia Reservoir |
| 投稿时间：2019-06-12 修订日期：2021-07-19 |
| DOI：10.15928/j.1674-3075.201906120154 |
| 中文关键词:乐昌峡水库 气体释放 声学信号 气泡特征 |
| 英文关键词:Lechangxia reservoir greenhouse gas emission hydroacoustic signal recognition bubbles feature |
| 基金项目:广州市科技计划项目(201707010448)；广东省渔港建设和渔业产业发展专项；中国水产科学研究院珠江水产研究所自主科技创新项目(EC-2019-6) |
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| 中文摘要: |
| 淡水湖泊和水库底部沉积物产生的甲烷（CH4）常以气泡方式从水中逸出，由于气泡目标强度（target strength,TS）分布范围与鱼类目标强度高度重合，导致信号误判而影响数据处理。2017年7月，使用分裂波束渔探仪Simrad EY60（120 kHz，200 W）在北江水系乐昌峡水库进行声学探测，研究不同航速下的信号类别，为水下气体跟踪、温室气体释放通量、水体底质演变及渔业资源评估提供参考依据。结果显示，气泡（多数）和鱼类（少数）为乐昌峡水库主要声学散射体，与鱼类信号的随机性相比，气泡更具有一定规律性，一直上升且水平位移较小，气泡与鱼类在相对游泳速度、垂直方向变化、目标轨迹的垂直变化等变量存在显著差异（P<0.01）。气泡在水中的平均上升速度为23.95 cm/s，95%置信区间为23.17~24.74 cm/s；平均气泡目标强度为-60.09 dB，分布范围为-73.82~-33.29 dB，半径范围0.20~21.65 mm；气泡在上升过程中速度逐渐减慢，半径逐渐减小，与水深呈显著相关关系（r=0.99，P＜0.01）。船速<3 km/h，回波图能清晰分辨气泡和鱼体信号，可作为目标运动轨迹识别依据。 |
| 英文摘要: |
| Substantial quantities of methane (CH4) can be produced in freshwater lake sediments and it is released as bubbles due to low water solubility. During hydroacoustic surveys, the target strength (TS) of bubbles strongly overlaps with that of fish and the signals can be misclassified during data processing of fishery resource surveys. In this study, Lechangxia reservoir was selected as a case study, and the bubble signals collected during hydroacoustic surveys were analyzed, focusing on signal features, motion rules and signal recognition. The objectives were to provide a reference for acoustic signal recognition and fishery resource assessment as well as for research on tracing and measurement of greenhouse gases released from bottom sediments. Acoustic surveys were conducted in Lechangxia reservoir on July 17 and 18 of 2017 using a Simrad EY60 echo sounder. A 120 kHz split beam downward-looking echosounder was used to collect different signals not resonating with the sonar frequency at different speeds. A slow ship speed (<3 km/h) significantly enhanced the quality of data and the ability to discriminate between bubbles and fish, based on differences in echogram trajectory. Analysis of the echogram indicated that gas bubbles (majority) and fish (minority) were the two primary echo-reflecting objects in the survey area. Significant differences were observed between fish and bubbles for several parameters; movement speed, vertical direction change and track change with depth (P<0.01). Bubbles were more regular and kept rising with a small horizontal displacement compared with fish. The average ascension speed of bubbles was 23.95 cm/s and the 95% confidence interval was 23.17-24.74 cm/s（n=360）. The average TS of the bubbles was -60.09 dB, ranging from -73.82 to -33.29 dB, and the radius ranged from 0.20 mm to 21.65 mm. The speed and radius of the bubbles decreased as bubbles ascended and the correlation with the water depth was significant (r=0.99，P＜0.01). At a cruising speed of <3 km/h, the bubbles and fish could be recognized clearly from the echogram and used to identify the target signal. Combing the results of our study with those from previous studies, it was concluded that bubbles are highly heterogeneous and exist widely in freshwater reservoirs and lakes, and that surveys should be designed based on the intended purpose when using acoustic technology. Hydroacoustic measurements provide a means of distinguishing the bubbles released in bottom sediments of lakes and reservoirs from fish and this should be considered when quantifying methane ebullition and fish abundance in aquatic systems. |
| 武 智,李新辉,谭细畅,李 捷,朱书礼,张迎秋.2021.淡水水体气泡的声学信号特征与识别研究 ——以乐昌峡水库为例[J].水生态学杂志,42(4):32-39. |
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