Study on inverting seagrass coverage ratio at Dongjiao Coconut Forest based on UAV aerial survey technology
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摘要: 海草盖度是反映海草床生态状况的重要指标。本文通过航拍方案设计和飞行条件试验采用无人机航拍获取了东郊椰林海域高分辨率海草影像图，结合ArcGIS软件影像分类工具和3D工具反演了海草分布范围，研究出海草盖度计算的新方法并计算了东郊椰林海底海草的盖度，模拟传统海草盖度调查方法的站点布置，探讨了其结果可比性和代表性问题。研究结果表明，东郊椰林海域海草主要分布于离岸300 m以内的珊瑚礁砰上，呈斑块状、间隔式分布，获取东郊椰林沿岸海草集中分布区面积为23 221 m2，占研究区面积的比例为17.79%；海草覆盖面积约为16 423 m2，海草盖度为12.58%，海草盖度较高，海草床生态状况良好。在研究区的东南区域有马尾藻密集分布，分布面积为755.6 m2，其盖度为0.5%，呈独株圆柱状漂浮生长。通过模拟试验，传统海草盖度调查方法有样框法和样线法，布置站点不同，样框、样线放置有随机性，海草盖度调查结果变动明显，是传统调查方法的结果存在代表性差、可比性差的原因。本研究成果在海草生态监控区调查中具有推广应用价值。
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关键词:
- 无人机航测 /
- 东郊椰林 /
- 海草盖度 /
- 最大似然法 /
- Iso聚类非监督分类
Abstract: Seagrass coverage ratio is an important indicator reflecting the ecological status of seagrass beds. In this paper, through the design of aerial photography scheme and flight condition test, the high-resolution seagrass image map of the Dongjiao Coconut Forest sea area was obtained by using UAV aerial photography. Combined with the image classification tools of ArcGIS software and 3D tools, a new method for calculating the coverage ratio of seagrass were obtained and the coverage of seagrass was calculated. The station location of simulating survey method of the traditional seagrass coverage ratio was compared and discussed. Seagrasses in the coastal sea bed of the Dongjiao Coconut Forest are distributed on the coral reefs within 300 m from the shore with patches and intervals. Using the new method, the concentrated distribution area of seagrass at sea bed of the Dongjiao Coconut Forest is about 23 221 m2, and average concentration distribution ratio is 17.79%. The distribution area of seagrass in this study area is about 16 423 m2, and the coverage ratio of seagrass is 12.58%. The coverage ratio of seagrass is higher, and the ecological condition of seagrass bed is good. Sargassum is densely distributed in the southeast area of the study area, with a distribution area of 755.6 m2 and a coverage of 0.5%, and grows as a single cylinder floating. By simulating the investigation station location of the sample frame method and sample line method of traditional seagrass coverage survey, seagrass coverage ratio changes with different stations, sample frame, and sample line positions changing randomly, which is the reason for the representativeness and comparability of the traditional survey results. The research results of this project have the promotion and application value in the investigation of seagrass ecological monitoring area. -
图 3 验证区域的海草分布（20 m, 无人机拍摄）
Fig. 3 Seaweed distribution in validation area (20 m, photo by UAV)
图 5 模拟调查站点布设
a. 样框法; b. 样线法
Fig. 5 Simulatively location of investigation station
a. Enclosing-square method；b. line transect method
图 7 研究区海草集中分布矢量图
Fig. 7 Vectorgraph of seagrass concentrated distribution at research area
图 9 不同情况下研究区的海草盖度
a. 样框法；b. 样线法
Fig. 9 Seagrass coverage ratio under different conditions at research area
a. Enclosing-square method；b. line transect method
表 1 无人机成像系统参数
Tab. 1 Unmanned aerial vehicle (UAV) imaging system parameters
参数 数值 飞行器 重量 1 391 g 最大起飞海拔高度 6 000 m 飞行时间 约30 min 工作环境因素 0～40℃ 相机 影像传感器 CMOS；有效像素2 000万 照片最大分辨率 5 472 × 3 648（3∶2） 
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表 2 研究区海草集中分布特征
Tab. 2 Concentrated distribution feature of seagrass at research area
区块 区块1 区块2 区块3 区块4 区块5 区块6 区块7 区块8 区块9 区块10 区块12 区块13 区块14 区块15 总计 海草集中面积/m2 413 1 076 897 593 152 1 427 2 413 2 176 2 219 912 376 2 813 4 433 3 310 23 221 海域面积/hm2 1 1 1 1 1 1 1 1 1 1 0.166 1 0.889 5 1 1 13.055 6 斑块数/个 292 405 539 232 109 55 64 83 59 38 28 53 23 34 2 014 集中分布比例/% 4.13 10.76 8.97 5.93 1.52 14.27 24.13 21.76 22.19 9.12 22.64 31.62 44.33 33.10 17.79
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表 3 海草盖度计算结果
Tab. 3 Calculation results of seagrass coverage rate
区块 区块1 区块2 区块3 区块4 区块5 区块6 区块7 区块8 区块9 区块10 区块12 区块13 区块14 区块15 总计 海草面积/m2 277 715 816 585 149 1 171 2 056 1 521 1 273 394 283 1 950 2 982 2 251 16 423 海域面积/hm2 1 1 1 1 1 1 1 1 1 1 0.166 1 0.889 5 1 1 13.055 6 海草盖度/% 2.77 7.15 8.16 5.85 1.49 11.71 20.56 15.21 12.73 3.94 17.03 21.92 29.82 22.51 12.58
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表 4 模拟站点样框的海草盖度
Tab. 4 Seagrass coverage ratio at simulative investigation stations enclosing-square
站点 海草面积与盖度 样框L1 样框L2 样框L3 样框L4 样框L5 样框L6 样框L7 样框L8 样框L9 样框L10 样框L11 总计 原站点 面积/m2 7.08 7.01 11.21 2.51 1.17 3.79 − 6.55 11.19 − − 50.51 盖度/% 28.32 28.04 44.84 10.03 4.68 15.16 − 26.2 44.76 − − 18.36 整体向东边平移50 m 面积/m2 − 6.83 3.79 10.18 − − − 0.17 0.30 − − 21.27 盖度/% − 27.32 15.16 40.72 − − − 0.68 1.2 − − 7.73 随后向南边平移50 m 面积/m2 − 2.91 13.61 1.89 0.88 − − − − − − 19.29 盖度/% − 11.64 54.44 7.56 3.52 − − − − − − 7.01 平均盖度/% 11.03 注：“−”表示未发现海草分布。
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表 5 模拟断面拉线调查属性表
Tab. 5 Property sheet of simulated cross-section cable survey
样线 海草长度和盖度 站点D1 站点D2 站点D3 小计 样线L1 样线L2 样线L3 平均/% 样线L1 样线L2 样线L3 平均/% 样线L1 样线L2 样线L3 平均/% 初始样线 海草长度/m 20.1 4.8 0.9 23.7 15.74 14.1 21.1 8.3 14.1 盖度/% 40.2 9.6 1.8 17.2 47.4 31.4 28.2 36.0 42.2 16.6 28.2 29.0 27.4 整体南移10 m 海草长度/m 8.2 0.3 2.7 6.6 4.1 6.5 10.8 4.0 6.5 盖度/% 16.4 0.6 5.4 7.5 13.2 8.2 13.0 11.5 21.4 8.0 13 14.2 11.1 整体向南平移20 m 海草长度/m 4.7 15.0 6.1 28.6 3.8 21.2 12.2 13.4 17.0 盖度/% 9.4 30.0 12.2 17.2 28.6 3.8 21.2 17.9 12.2 13.4 17.0 14.2 16.4 整体向南平移30 m 海草长度/m 2.7 8.3 0.2 13.6 6.8 7.4 24.5 21.5 15.6 盖度/% 5.4 16.6 0.4 7.5 27.2 13.6 14.8 18.5 49.0 43.0 31.2 41.1 22.4 平均/% 12.4 21.0 24.6 19.31
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