High-Resolution Mapping and Biomass Estimation of Suaeda salsa in Coastal Wetlands Using UAV Visible-Light Imagery and Hue Angle Inversion
Abstract
1. Introduction
2. Materials and Methods
2.1. The Experimental Area
2.2. Design of Experiments
- (a)
- Experimental Site Setup (Figure 3a): Prior to measurements, the area with the highest density of Suaeda salsa was identified and designated as the initial quadrat, representing the maximum biomass. The quadrat was then secured, and DRSPs were positioned in an adjacent open area for calibration purposes.
- (b)
- UAV Camera Parameter Configuration and Initial Imaging: To ensure consistent illumination throughout data collection, the visible-light camera’s exposure settings—including aperture, shutter speed, and ISO—were fixed before flight. A single-frame shooting mode was employed to capture high-resolution imagery of the Suaeda salsa quadrat.
- (c)
- Sequential UAV Imaging and Biomass Removal (Figure 3b): The UAV ascended to a fixed altitude of approximately 25 m to capture an initial image of the quadrat at its maximum Suaeda salsa biomass. Subsequently, portions of Suaeda salsa within the quadrat were evenly removed to incrementally reduce biomass. After each removal, another UAV image was captured, and the removed plant material was sealed in labeled bags for subsequent biomass analysis. This iterative process of incremental Suaeda salsa removal, UAV image acquisition, and sample storage continued until the quadrat was completely cleared.
- (d)
- Laboratory Processing of Biomass Samples: Upon the completion of UAV imaging, all plant samples were promptly transported to the laboratory. Roots were thoroughly rinsed with clean water to remove soil residues. Each sample was then wrapped in aluminum foil and oven-dried to a constant weight, and its dry biomass was meticulously recorded according to the sample labels.
- (e)
- Image Processing: For each UAV image, the quadrat-corresponding area was accurately extracted. The hue angle was subsequently calculated for this region, and the average hue angle was determined for further analysis.
- (f)
- Model Dataset Construction: Based on the sequential biomass removal, the Suaeda salsa biomass within the quadrat (expressed in kg/m2) was calculated for each UAV capture. This yielded a robust modeling dataset linking varying biomass levels with their corresponding mean hue angles.
2.3. Data Preprocessing
2.3.1. Reflectance Conversion Method
2.3.2. Methods for Calculating Hue Angle
2.4. Evaluation Method
3. Results
3.1. Reflectance Conversion
3.2. Hue Angle Cutoff Threshold
3.3. Inversion Model Construction
4. Discussion
4.1. Applying Vegetation Indices to Extract Suaeda salsa from UAV Imagery
4.2. Factors Influencing Quantitative Inversion Using UAV Visible Imagery
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Model Type | Model Expression | R2 | MAPE (%) | RMSE (kg/m2) |
---|---|---|---|---|
Linear function | Biomass = −8.87436 + 0.03512 × α | 0.93650 | 12.985 | 0.09966 |
Quadratic polynomial function | Biomass = 136.68861 − 1.07788 × α + 0.00213 × α2 | 0.99124 | 91.346 | 0.55293 |
Exponential function | Biomass = 3.57639 × 10−15 × e0.12201×α | 0.99696 | 3.616 | 0.02183 |
Power function | Biomass = 4.51642 × 10−79 × α32.16447 | 0.99674 | 3.554 | 0.02258 |
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Wang, L.; Wang, X.; Su, X.; Wen, S.; Wang, X.; Meng, Q.; Jiang, L. High-Resolution Mapping and Biomass Estimation of Suaeda salsa in Coastal Wetlands Using UAV Visible-Light Imagery and Hue Angle Inversion. Appl. Sci. 2025, 15, 7423. https://doi.org/10.3390/app15137423
Wang L, Wang X, Su X, Wen S, Wang X, Meng Q, Jiang L. High-Resolution Mapping and Biomass Estimation of Suaeda salsa in Coastal Wetlands Using UAV Visible-Light Imagery and Hue Angle Inversion. Applied Sciences. 2025; 15(13):7423. https://doi.org/10.3390/app15137423
Chicago/Turabian StyleWang, Lin, Xiang Wang, Xiu Su, Shiyong Wen, Xinxin Wang, Qinghui Meng, and Lingling Jiang. 2025. "High-Resolution Mapping and Biomass Estimation of Suaeda salsa in Coastal Wetlands Using UAV Visible-Light Imagery and Hue Angle Inversion" Applied Sciences 15, no. 13: 7423. https://doi.org/10.3390/app15137423
APA StyleWang, L., Wang, X., Su, X., Wen, S., Wang, X., Meng, Q., & Jiang, L. (2025). High-Resolution Mapping and Biomass Estimation of Suaeda salsa in Coastal Wetlands Using UAV Visible-Light Imagery and Hue Angle Inversion. Applied Sciences, 15(13), 7423. https://doi.org/10.3390/app15137423