Journal of Geo-information Science >
Topographic Retrieval of the Tidal Flats in the Yangtze Estuary based on the Dynamic Tidal Submergence
Received date: 2021-07-27
Request revised date: 2021-09-01
Online published: 2022-05-25
Supported by
National Natural Science Foundation of China(41801393)
Special Project of Central Government Guiding Local Development(2017L3012)
Copyright
Tidal flats are important transitional zones between terrestrial and marine ecosystems and have complicated ecological processes and essential ecosystem services. Tidal flats are highly dynamic under the influences of land-sea interactions and anthropogenic activities. Limited by the accessibility, it is difficult to map the tidal flat using traditional survey. To solve the difficulty in obtaining tidal flat elevation data, a tidal flat elevation inversion model suitable for large-scale with high accuracy is needed. In this study, we proposed an algorithm incorporating tidal submergence and time-series Remote Sensing (RS) data to map the topography of tidal flats. We used Chongming Dongtan as an example and further extended the results to the whole Yangtze Estuary. Firstly, the K-means++ clustering was employed to extract the inundation extent of tidal. Then, the frequency of tidal inundation of each pixel was calculated from the time series RS data. Finally, the tidal flat topography was retrieved based on the regional tidal frequency. All available Sentinel-2 and Landsat-8 images from 2016 to 2020 were used to build the time-series dynamic of tidal flats to map the topography. Verified by the in-situ data, the results showed that the total accuracy and F1-score of the inundation extent extraction of the tidal flats were 97.73% and 0.98, respectively. The average absolute error of elevation inversion was 0.15 m. The accuracy of tidal flat elevation was positively correlated with the number of available images. The total area of tidal flats was 346.93 km2 with an elevation range of 1.00~3.84 m. The tidal flats in the Yangtze Estuary were mainly distributed in Chongming Dongtan, Jiuduansha, Hengsha Dongtan, Nanhui Biantan, and Tuanjiesha. Among them, Nanhui beach had the largest area (107.44 km2), while Chongming east beach had the largest elevation difference (2.84 m). The distribution status of tidal flat was mainly affected by sediment hydrodynamics, vegetation, and human engineering activities. Compared with the existing dataset, our results showed a more robust capacity in the inundation extent extraction of tidal flats. With the increasing number of effective observations and tidal level information from time-series RS images in coastal areas, the extraction accuracy of tidal flat information could be further improved. The proposed algorithm has a great potential in rapid mapping of tidal flat topography and is of great significance for the dynamic monitoring and management of tidal flat resources.
ZHANG Min , WU Wenting , WANG Xiaoqin , SUN Yu . Topographic Retrieval of the Tidal Flats in the Yangtze Estuary based on the Dynamic Tidal Submergence[J]. Journal of Geo-information Science, 2022 , 24(3) : 583 -596 . DOI: 10.12082/dqxxkx.2022.210429
表1 各区域影像数量及潮位信息Tab. 1 The number of images and tidal range of the subareas |
区域 | 数量/景 | 相对最高潮/m | 相对最低潮/m |
---|---|---|---|
A1 | 115 | 3.94 | 0.92 |
A2 | 101 | 3.95 | 1.08 |
A3 | 81 | 3.39 | 1.33 |
A4 | 90 | 3.18 | 1.41 |
A5 | 111 | 3.21 | 1.37 |
A6 | 104 | 3.34 | 1.39 |
A7 | 86 | 3.47 | 1.41 |
注:潮位高程基准为吴淞高程。 |
表2 潮滩范围提取验证Tab. 2 the verification of extent mapping of tidal flats |
类别 | 潮滩 | 非潮滩 | 合计 | 用户精度/% | F1_score | 总体精度/% |
---|---|---|---|---|---|---|
潮滩 | 300 | 1 | 301 | 99.67 | 0.98 | 97.73 |
非潮滩 | 12 | 261 | 273 | 95.60 | 0.97 | |
合计 | 312 | 262 | 574 | |||
生产精度/% | 96.15 | 99.62 |
图9 长江口各区域潮滩高程分布特征。Fig. 9 The spatial distribution of the retrieval elevation of the flats in the Yangtze Estuary |
表3 各潮滩面积和高程范围Tab. 3 The area and elevation range of each tidal flat |
潮滩区域 | 面积/km2 | 高程范围/m |
---|---|---|
崇明岛 | 97.59 | 1.00~3.84 |
团结沙 | 34.56 | 1.36~2.66 |
横沙岛 | 29.94 | 1.48~3.11 |
九段沙 | 68.72 | 1.48~3.25 |
江亚南沙 | 8.68 | 1.48~3.13 |
南汇东滩 | 107.44 | 1.49~3.39 |
合计 | 346.93 | 1.00~3.84 |
表4 各高程范围下的潮滩面积Tab. 4 Tidal flat area of each elevation range |
高程范围/m | 面积/km2 | 高程范围/m | 面积/km2 | |
---|---|---|---|---|
1.00~1.20 | 4.61 | 2.60~2.80 | 23.05 | |
1.20~1.40 | 21.69 | 2.80~3.00 | 26.14 | |
1.40~1.60 | 39.66 | 3.00~3.20 | 29.33 | |
1.60~1.80 | 44.76 | 3.20~3.40 | 15.80 | |
1.80~2.00 | 39.40 | 3.40~3.60 | 5.79 | |
2.00~2.20 | 32.35 | 3.60~3.80 | 9.50 | |
2.20~2.40 | 28.02 | 3.80~3.84 | 3.42 | |
2.40~2.60 | 23.92 |
表5 影像数量差异对比Tab. 5 Comparison of the number of images |
影像数量/景 | R2 | RMSE/m |
---|---|---|
101 | 0.92 | 0.19 |
60 | 0.86 | 0.21 |
32 | 0.83 | 0.32 |
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