研究目的
To investigate the possibility of individual tree detection and delineation (ITDD) for mangroves using UAV-based LiDAR data, specifically to detect and measure tree height and crown diameter, and analyze the impact of crown clumping density and spatial resolution on ITDD accuracy.
研究成果
The study successfully demonstrated the feasibility of using UAV-based LiDAR for mangrove ITDD with promising accuracy (46% detection accuracy). Isolated trees were delineated with the highest accuracy, and spatial resolution finer than one-fourth of crown diameter is recommended for optimal results. Challenges include under-detection due to clumping density, and future work should focus on algorithm improvements and data fusion with other remote sensing techniques.
研究不足
The study faced challenges such as uneven LiDAR point density, difficulty in distinguishing clumped mangroves due to high density and small height differences, errors in field measurements, time differences between field and UAV data collection, and limitations in algorithm performance for complex crown structures. Recommendations include improving CHM accuracy, better mangrove masking, and combining with other data types like imagery and terrestrial LiDAR.
1:Experimental Design and Method Selection:
The study used UAV-based LiDAR data with high point density (91 pt./m2) to generate canopy height models (CHMs) at four spatial resolutions (
2:1 m, 25 m, 5 m, 1 m). ITDD was performed using variable window filtering for treetop detection and two algorithms for crown delineation:
seeded region growing (SRG) and marker-controlled watershed segmentation (MCWS).
3:Sample Selection and Data Sources:
Field measurements of 126 mangrove trees were conducted in Guangxi, China, including location, height, and crown diameter. Trees were categorized into three clumpingness groups: isolated, boundary, and clumped.
4:List of Experimental Equipment and Materials:
UAV LiDAR system (Li-Air with Velodyne HDL-32E scanner), UAV with Sony a6000 camera, RTK-GPS for field measurements, software including ArcMap 10.5.1, MATLAB 2017a, and TerraScan for data processing.
5:1, MATLAB 2017a, and TerraScan for data processing.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: LiDAR data was processed to generate CHMs, non-mangrove areas were masked using a height threshold, treetops were detected, crowns were delineated using SRG and MCWS, and parameters (TH, CD) were extracted. Accuracy was assessed using detection accuracy and error metrics.
6:Data Analysis Methods:
Statistical analysis included linear regression, bias, RMSE, and relative errors. Simulation was used to assess the impact of spatial resolution on crown diameter estimation.
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