An Automatic Algorithm for Mapping Algal Blooms and Aquatic Vegetation Using Sentinel-1 SAR and Sentinel-2 MSI Data
Abstract
:1. Introduction
2. Materials
2.1. Study Area
2.2. Satellite Data
2.3. Field Data
3. Method
3.1. Mapping SAV
3.2. Mapping FEAV and AB
3.3. Assessment of Algorithm
- (1)
- Accuracy assessment based on field measured data. Confusion matrices were obtained between measured classes from field measured data and mapped classes derived from the algorithm proposed in this study, and overall accuracy (OA), Kappa, user accuracy (UA) and producer accuracy (PA) were calculated [36].
- (2)
- Assessment by phenological features of aquatic vegetation. For lakes lacking FEAV and SAV samples, indirect validation was conducted by phenological feature of FEAV and SAV. Specifically, in a short timeframe, FEAV and SAV exhibit fixed spatial distribution and limited area change [37]. The similarity in spatial distribution of FEAV and SAV between adjacent temporally sequential images was assessed by Dice Coefficient [38] (Equation (8)).
4. Result
4.1. Validations of Algorithm
4.1.1. Validations by Field Measured Data
4.1.2. Assessment by Phenological Feature
4.1.3. Comparison with Published Maps
4.2. Algorithm Applications
5. Discussion
5.1. Advantages
5.2. Limitations
5.3. Implications
6. Conclusions
Supplementary Materials
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Lake Name | Survey Date | Image Date | SAV Samples | FEAV Samples | AB Samples | OW Samples |
---|---|---|---|---|---|---|
Taihu | 17 August 2019 | 17 August 2019 | 624 | 1445 | 1368 | 356 |
5 September 2020 | 5 September 2020 | 596 | 1533 | 1107 | 333 | |
Chaohu | 15 September 2019 | 19 September 2019 | 74 | 100 | 293 | 108 |
Hongze | 24 August 2019 | 20 August 2019 | 110 | 281 | / | 202 |
25 August 2019 | ||||||
Total | / | / | 1404 | 3359 | 2768 | 999 |
Lake Name/ Image Date | Measured Class | |||||||
---|---|---|---|---|---|---|---|---|
Taihu 17 August 2019 | SAV | FEAV | AB | OW | Sum | UA (%) | ||
Map class | SAV | 208 | 4 | 12 | 9 | 233 | 89.27 | |
FEAV | 11 | 454 | 29 | 0 | 494 | 91.9 | ||
AB | 21 | 27 | 406 | 17 | 471 | 86.19 | ||
OW | 14 | 0 | 21 | 330 | 365 | 90.41 | ||
Sum | 254 | 485 | 468 | 356 | 1563 | |||
PA (%) | 81.89 | 93.61 | 86.75 | 92.7 | ||||
OA = 89.44%; Kappa = 0.86 | ||||||||
Taihu 5 September 2020 | SAV | FEAV | AB | OW | Sum | UA (%) | ||
Map class | SAV | 319 | 7 | 13 | 2 | 341 | 93.55 | |
FEAV | 8 | 489 | 17 | 0 | 514 | 95.13 | ||
AB | 9 | 22 | 329 | 19 | 379 | 86.81 | ||
OW | 11 | 0 | 23 | 312 | 346 | 90.17 | ||
Sum | 347 | 518 | 382 | 333 | 1580 | |||
PA (%) | 91.92 | 94.4 | 86.13 | 93.69 | ||||
OA = 91.72%; Kappa = 0.89 | ||||||||
Chaohu 19 September 2019 | SAV | FEAV | AB | OW | Sum | UA (%) | ||
Map class | SAV | 71 | 2 | 1 | 0 | 74 | 95.95 | |
FEAV | 0 | 90 | 0 | 0 | 90 | 100 | ||
AB | 3 | 8 | 279 | 16 | 306 | 91.18 | ||
OW | 0 | 0 | 13 | 92 | 105 | 87.62 | ||
Sum | 74 | 100 | 293 | 108 | 575 | |||
PA (%) | 95.95 | 90 | 95.22 | 85.19 | ||||
OA = 82.61%; Kappa = 0.73 | ||||||||
Hongze 20 August 2019 | SAV | FEAV | AB | OW | Sum | UA (%) | ||
Map class | SAV | 103 | 6 | \ | 2 | 111 | 92.79 | |
FEAV | 1 | 272 | \ | 0 | 273 | 99.63 | ||
AB | \ | \ | \ | \ | \ | \ | ||
OW | 6 | 3 | \ | 200 | 209 | 95.69 | ||
Sum | 110 | 281 | \ | 202 | 593 | |||
PA (%) | 93.64 | 96.8 | \ | 99.01 | ||||
OA = 86.84%; Kappa = 0.79 |
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Xin, Y.; Luo, J.; Zhai, J.; Wang, K.; Xu, Y.; Qin, H.; Chen, C.; You, B.; Cao, Q. An Automatic Algorithm for Mapping Algal Blooms and Aquatic Vegetation Using Sentinel-1 SAR and Sentinel-2 MSI Data. Land 2025, 14, 592. https://doi.org/10.3390/land14030592
Xin Y, Luo J, Zhai J, Wang K, Xu Y, Qin H, Chen C, You B, Cao Q. An Automatic Algorithm for Mapping Algal Blooms and Aquatic Vegetation Using Sentinel-1 SAR and Sentinel-2 MSI Data. Land. 2025; 14(3):592. https://doi.org/10.3390/land14030592
Chicago/Turabian StyleXin, Yihao, Juhua Luo, Jinlong Zhai, Kang Wang, Ying Xu, Haitao Qin, Chao Chen, Bensheng You, and Qing Cao. 2025. "An Automatic Algorithm for Mapping Algal Blooms and Aquatic Vegetation Using Sentinel-1 SAR and Sentinel-2 MSI Data" Land 14, no. 3: 592. https://doi.org/10.3390/land14030592
APA StyleXin, Y., Luo, J., Zhai, J., Wang, K., Xu, Y., Qin, H., Chen, C., You, B., & Cao, Q. (2025). An Automatic Algorithm for Mapping Algal Blooms and Aquatic Vegetation Using Sentinel-1 SAR and Sentinel-2 MSI Data. Land, 14(3), 592. https://doi.org/10.3390/land14030592