This document summarizes a study that used unmanned aerial vehicles (UAVs) and photogrammetry techniques to monitor the evolution of an active fan in Southwestern Taiwan over time. Key findings include: 1) UAVs were able to efficiently collect high-resolution aerial photos of the fan area, which were then used to create detailed digital elevation models and thickness maps showing changes to the fan's deposits and channels over multiple flood events. 2) Comparisons of the UAV-generated models with ground surveys found errors within an acceptable range, validating the use of this low-cost photogrammetry method for monitoring fan changes. 3) The completed study demonstrated both the advantages and limitations of using UAVs

1. Field monitoring of an active fan using UAV photogrammetry
UAV workshop 2017/05/09
Hervé Capart
NTU Dept of Civil Engineering

2. Field site: Laonong River, Southwestern Taiwan 2

3. 3Valley setting 3

4. 2009-05-09 2009-08-17
(Satellite image source: FORMOSAT-2, NSPO)

5. Fan evolution observations 5
(Credit:BruceJ.B.H.Shyu)(Credit:M.L.Hsieh)

6. Fan evolution observations 6

7. Carbon 14 dating of past fan deposits 7
(Credit:M.L.Hsieh)

8. Fan activity: upstream canyon backfill 8
Photosource:ForestBureau

9. Fan activity: upstream canyon backfill 9

10. Fan activity: debris channel avulsion 10

11. Fan activity: debris channel avulsion 11

12. Fan activity: damming of trunk river 12

13. Fan activity: damming of trunk river 13

14. Photo credit: Hsieh M.L.
14Fan activity: damming of trunk river

15. Fan activity: undermining of opposite bank 15

16. Elevated roadway proposal 16
Image credit: CECI

17. Elevated roadway proposal 17
山脊高程
EL.640m
山脊高程
EL.660m
河床便道
EL.620~640m
起點 97k+300
終點 98k+500
Image credit: CECI

18. Lab experiments (Chien-Ling Huang) 18

19. Multiple successive events 19
ScouredFresh

20. Photogrammetry concept 20

21. Photogrammetry using mirror array 21

22. Photogrammetry using mirror array 22
Mirror image Reconstructed DEM

23. Deposit thickness maps 23
ScouredFresh

24. Mathematical theory (Yiling Chen) 24

25. Field photogrammetry using UAV (Ray Wen and Jason Yang) 25

26. Photo by Ming-Chang Wen
UAV specifications 26
Maximum loading 12 kg (general 7 kg)
Maximum fly time 30 minute
Maximum fly altitude 1. 5 Km
Maximum remote
distance
Approximate 4 km
Six-Propeller UAV
Twin-gyro stabilizer

27. Ground control points 27
Total marker
used
27
1000 m500 m0

28. Flight scheme 28

29. Merged analysis results (Chien-Ling Huang) 29
Resolution 0.3 m
GCP Error 0.1 m

30. Qualitative comparison 30

31. Quantitative comparison with total station transects 31
580 590 600 610 620 630 640 650
590
600
610
620
630
640
Elevation of Total station field survey (m)
ElevationofPhotogrammetryDTM(m)
elevation sample point
r =1.0004
655 660 665 670 675 680 685 690
660
665
670
675
680
685
Elevation of Total station field survey (m)
ElevationofPhotogrammetryDTM(m)
elevation sample point
R=0.99786

32. Difference map 32

33. Advantages and limitations of UAV photogrammetry 33
Advantages:
-Quick deployment
-Low cost
-Good accuracy
-High resolution
-Survey crew safety
Limitations:
-Need for ground control points
-Limited distance and relief range
-Ground occlusion by vegetation

34. Completed elevated roadway (opened to traffic 2017-04-29) 34
Photo courtesy C. C. Chern

35. Acknowledgements 35
Prof. Shih-Chung Jessy Kang’s CAE group and in particular
Ming-Chang (Ray) Wen and Cheng Hsuan (Jason) Yang
The NTU-CE morphohydraulics research group
and in particular Chien-Ling Huang and Yiling Chen