Extraction of Urban Objects in Cloud Shadows on the basis of Fusion of Airborne LiDAR and Hyperspectral Data
<p>False color composite of hyperspectral imagery (<b>top</b>) and the normalized digital surface model (nDSM) derived from LiDAR data (<b>bottom</b>).</p> "> Figure 2
<p>Flowchart of the proposed method.</p> "> Figure 3
<p>Hyperspectral imagery in cloud-shadow areas, true color display (<b>left</b>) and false color display (<b>right</b>).</p> "> Figure 4
<p>The flowchart of urban object extraction from shadow areas with the fusion of airborne light detection and ranging (LiDAR) and hyperspectral data.</p> "> Figure 5
<p>Spectral curve of vegetation in shadow areas. Here, red/green/yellow lines represent max/mean/min values of hyperspectral data, respectively. The longitudinal axis represents radiance, and the transverse axis represents wavelength (nm).</p> "> Figure 6
<p>Normalized difference vegetation index (NDVI) imagery of the shadow area (<b>left</b>) and the distribution of vegetation samples in different intervals of the NDVI (<b>right</b>). Here, longitudinal and transverse axes represent the number of samples and NDVI, respectively.</p> "> Figure 7
<p>Optimal classified hyperplane (<b>left</b>) and Normalization Optimal classified hyperplane (<b>right</b>).</p> "> Figure 8
<p>Classified maps in the shadow area obtained from object-based classification (<b>left</b>) and the traditional pixel-based support vector machine (SVM) classifier (<b>right</b>).</p> "> Figure 9
<p>The nDSM imagery of the cloud shadow area (<b>left</b>) and the hyperspectral data of the cloud shadow area (<b>right</b>).</p> "> Figure 10
<p>The traditional pixel-based SVM classified map of the whole study area (<b>top</b>) and the final decision fusion classification map (<b>bottom</b>).</p> "> Figure 11
<p>A comparison of the classified results in the shadow area between the traditional pixel-based SVM classifier (<b>left</b>) and the proposed object-based classification method (<b>right</b>).</p> ">
Abstract
:1. Introduction
2. Study Area and Data
2.1. Study Site
2.2. Datasets
2.2.1. LiDAR Data
2.2.2. Hyperspectral Data
2.2.3. Training and Validation Data
3. Methodology
3.1. Data Preprocessing
3.2. Shadow Area Extraction
3.3. Extraction of Urban Objects in Cloud Shadow Areas
3.3.1 Image Segmentation
3.3.2. Classification Algorithms
- Mean nDSM ≥ 2 m and Mean NDVI ≤ 0.4;
- Merge the extracted segments;
- Length ≤ 450 m and Length/Width ≤ 10;
- Area ≥ 95 m2.
- Mean NDVI ≥ 0.4 and Mean nDSM ≥ 1 m;
- Merge the extracted segments;
- Area ≥ 5 m2.
- Mean NDVI ≥ 0.4 and Mean nDSM < 0.5 m;
- Assign the non-extracted objects to unclassified.
- 10 ≤ Intensity ≤ 71;
- Merge the extracted segments;
- Length ≥ 750 m;
- 2100 m2 < Area < 55,000 m2.
- Mean nDSM ≥ 0 m;
- 55 < Intensity < 100;
- Merge the extracted segments;
- 125 m ≤ Length ≤ 500 m;
- 2.2 ≤ compactness ≤ 2.4.
- Mean nDSM ≥ 0m;
- Mean Intensity ≥ 10;
- 100 m ≤Length ≤ 300 m;
3.4. Extraction of Urban Objects in the Whole Study Area
3.5. Decision Fusion
- (1)
- Subset with the boundary of the shadow areas;
- (2)
- The class code of the urban objects in defined as trees, buildings, grass, highway, and railway was set to 0, and the class code of the other objects was set to 1;
- (3)
- The raster calculator in ArcGIS 10.2 software was used to multiple (1) by (2);
- (4)
- The class code of the other objects was set to 0;
- (5)
- The raster calculator was used to add (3) and (4).
3.6. Accuracy Assessment
4. Results and Discussion
4.1. Classification Results of Cloud Shadow Areas
4.2. The Decision-fusion Result of the Whole Study Area
4.3. Accuracy Assessment of the Final Decision Fusion Result
4.4. Discussion
5. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Sample No. | Class | Training | Validation | ||
---|---|---|---|---|---|
No. of Polygons | No. of Pixels | No. of Polygons | No. of Pixels | ||
1 | grass | 27 | 352 | 50 | 1731 |
2 | grass_synthetic | 2 | 192 | 1 | 505 |
3 | road | 14 | 140 | 35 | 891 |
4 | soil | 13 | 186 | 20 | 1056 |
5 | railway | 1 | 31 | 7 | 293 |
6 | parking_lot | 26 | 376 | 33 | 1306 |
7 | tennis_ court | 2 | 181 | 3 | 247 |
8 | running_track | 2 | 187 | 5 | 473 |
9 | water | 7 | 182 | 7 | 143 |
10 | trees | 15 | 173 | 49 | 880 |
11 | building | 51 | 341 | 100 | 1289 |
12 | highway | 5 | 109 | 7 | 299 |
Data | SVM | SVM + OB | ||
---|---|---|---|---|
OA (%) | Kappa Coefficient | OA (%) | Kappa Coefficient | |
hyperspectral + LiDAR | 87.30% | 0.85 | 92.30% | 0.91 |
Classes | SVM | SVM + OB | ||||
---|---|---|---|---|---|---|
PA (%) | UA (%) | AI (%) | PA (%) | UA (%) | AI (%) | |
grass_synthetic | 98.94 | 100.00 | 98.93 | 98.94 | 100.00 | 98.93 |
tree | 90.61 | 99.09 | 88.71 | 97.12 | 96.58 | 93.49 |
soil | 100.00 | 98.23 | 98.20 | 100.00 | 98.23 | 98.20 |
water | 98.60 | 100.00 | 98.58 | 98.60 | 100.00 | 98.58 |
road | 71.42 | 88.85 | 47.42 | 71.42 | 88.85 | 47.42 |
highway | 57.58 | 83.63 | 6.76 | 89.54 | 88.82 | 75.72 |
railway | 96.85 | 71.35 | 56.58 | 96.02 | 85.44 | 78.81 |
tennis_court | 100.00 | 92.31 | 91.66 | 100.00 | 92.31 | 91.66 |
running_track | 98.77 | 99.65 | 98.40 | 98.77 | 99.65 | 98.40 |
grass | 94.18 | 99.57 | 93.38 | 98.98 | 99.22 | 98.17 |
building | 88.95 | 80.69 | 63.64 | 94.50 | 92.85 | 86.08 |
parking_lot | 81.02 | 75.57 | 44.25 | 81.02 | 79.75 | 51.18 |
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Man, Q.; Dong, P. Extraction of Urban Objects in Cloud Shadows on the basis of Fusion of Airborne LiDAR and Hyperspectral Data. Remote Sens. 2019, 11, 713. https://doi.org/10.3390/rs11060713
Man Q, Dong P. Extraction of Urban Objects in Cloud Shadows on the basis of Fusion of Airborne LiDAR and Hyperspectral Data. Remote Sensing. 2019; 11(6):713. https://doi.org/10.3390/rs11060713
Chicago/Turabian StyleMan, Qixia, and Pinliang Dong. 2019. "Extraction of Urban Objects in Cloud Shadows on the basis of Fusion of Airborne LiDAR and Hyperspectral Data" Remote Sensing 11, no. 6: 713. https://doi.org/10.3390/rs11060713
APA StyleMan, Q., & Dong, P. (2019). Extraction of Urban Objects in Cloud Shadows on the basis of Fusion of Airborne LiDAR and Hyperspectral Data. Remote Sensing, 11(6), 713. https://doi.org/10.3390/rs11060713