Quantification of Agricultural Terrace Degradation in the Loess Plateau Using UAV-Based Digital Elevation Model and Imagery
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Data Acquisition
2.3. Evaluation of Terrace Degradation
2.3.1. Extraction of Terrace Ridges
- Step 1.
- The DEMs of the study areas are filled with depressions. The slope values of the DEMs are mapped with grayscale values ranging from 0 to 255. The generated images are smoothed by a Gaussian filter with the size of 5.
- Step 2.
- The gradients in the x and y directions, Gradx(x, y) and Grady(x, y), are calculated by Sobel operations. Then, the image gradient Grad(x, y) and gradient direction θ are calculated.
- Step 3.
- Nonmaximum suppression should be applied based on the gradient direction. If the gradient value of the pixel is less than that of two adjacent pixels in the gradient direction, the value of this pixel is set to 0, indicating that this pixel is not on the edges.
- Step 4.
- The high and low thresholds are calculated adaptively. The calculation formula of the high threshold is as follows:
- Step 5.
- The strong and weak edges are connected. The pixels with a gradient greater than the high threshold Th form strong edges. The pixels with a gradient between the high threshold Th and the low threshold Tl form weak edges. The pixels with a gradient lower than Tl form the background. If the weak edge is connected to the strong edge, the weak edge is identified as the edge; otherwise, the weak edge is converted into the background.
2.3.2. Reconstruction of Undamaged Terrace DEM
2.3.3. Calculation of Damage Degree of Terraces
3. Results
3.1. Extraction Results of Terrace Ridges
3.2. DEM Reconstruction Results
3.3. Damage Degree of Terraces
3.3.1. Damage Degree of Terrace Ridges
3.3.2. Damage Degree of Terrace Surfaces
3.3.3. Damage Degree of a Whole Terrace
4. Discussion
4.1. Rationality of the Proposed Method
4.2. Influence of DEM Resolution on Extracting Terrace Ridges
5. Conclusions
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Study Area | S1 | S2 | S3 |
---|---|---|---|
Average Altitude (m) | 1026.13 | 1042.78 | 1068.50 |
Average Slope (°) | 28.7 | 35.52 | 25.9 |
Average Wall Height (m) | 3.19 | 3.5 | 3.79 |
Average Platform Width (m) | 4.86 | 4.99 | 6.36 |
Area (ha) | 2.82 | 5.44 | 6.45 |
Study Areas | S1 | S2 | S3 |
---|---|---|---|
Completeness | 103.01% | 121.47% | 127.88% |
Correctness | 93.54% | 50.68% | 71.63% |
Quality | 96.17% | 55.67% | 85.03% |
Damage Degree of Terrace Ridges | Percentage in First Study Area (%) | Percentage in Second Study Area (%) | Percentage in Third Study Area (%) |
---|---|---|---|
0–1 | 5.8 | 5.41 | 7.94 |
1–3 | 20.29 | 18.92 | 19.05 |
3–5 | 14.49 | 8.11 | 12.7 |
5–10 | 37.68 | 37.84 | 20.63 |
10–20 | 20.29 | 21.62 | 31.75 |
20–30 | 1.45 | 8.11 | 4.76 |
>30 | 0 | 0 | 3.17 |
Damage Degree of Terrace Surfaces | Percentage in First Study Area (%) | Percentage in Second Study Area (%) | Percentage in Third Study Area (%) |
---|---|---|---|
<−1 | 0 | 0.08 | 0 |
−1~−0.5 | 0.57 | 2.66 | 6.77 |
−0.5~0 | 47.89 | 23.01 | 40.77 |
0~0.5 | 46.2 | 50.64 | 46.77 |
0.5~1 | 5.04 | 13.61 | 4.44 |
1~1.5 | 0.29 | 4.38 | 1.21 |
1.5~2 | 0 | 2.47 | 0.05 |
2~2.5 | 0 | 1.92 | 0 |
>2.5 | 0 | 1.23 | 0 |
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Fang, X.; Gu, Z.; Zhu, Y. Quantification of Agricultural Terrace Degradation in the Loess Plateau Using UAV-Based Digital Elevation Model and Imagery. Sustainability 2023, 15, 10800. https://doi.org/10.3390/su151410800
Fang X, Gu Z, Zhu Y. Quantification of Agricultural Terrace Degradation in the Loess Plateau Using UAV-Based Digital Elevation Model and Imagery. Sustainability. 2023; 15(14):10800. https://doi.org/10.3390/su151410800
Chicago/Turabian StyleFang, Xuan, Zhujun Gu, and Ying Zhu. 2023. "Quantification of Agricultural Terrace Degradation in the Loess Plateau Using UAV-Based Digital Elevation Model and Imagery" Sustainability 15, no. 14: 10800. https://doi.org/10.3390/su151410800