Landslide Monitoring in Three Gorges Area By Joint Use of Phase Based and Amplitude Based Methods

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1 Landslide Monitoring in Three Gorges Area By Joint Use of Phase Based and Amplitude Based Methods Xuguo Shi, Lu Zhang, Mingsheng Liao, Timo Balz LIESMARS, Wuhan University

2 Outlines Introduction InSAR Results Pixel Offset Tracking Results Summary

3 Part 1: Introduction

4 Dam Test Site: Three Gorges area (Began to function in 2003) Reservoir impoundment events along with dam construction/operation 135m 156m 175m 185m 66m

5 Geohazards in the Three Gorges area Adapted from Liu et al., 2009 dominant 67% of total

6 Difficulties for landslide monitoring in TG Steep terrain Dense vegetation cover Complicated atmospheric condition

7 Part 2: Datasets and InSAR Results

8 TerraSAR-X datasets HS: High resolution Spotlight SM: StripMap

9 Basic parameters SM data HS data Orbit direction Descending Descending Heading Look angle( ) Polarization VV HH Azimuth spacing(m) Range spacing(m) Temporal Coverage Jul 2008-May 2010 Jan 2009-Apr 2010

10 Locations of major landslides N Rg Az Kaziwan Shuping Fanjiaping Xintan Qianjiangping Lianziya Mean amplitude of 34 TerrraSAR-X StripMap images

11 What can InSAR do in landslide monitoring? What can InSAR observe? InSAR is useful for monitoring slow moving landslides!

12 TerraSAR-X Interferogram (SM mode) N Rg Az Kaziwan Shuping Fanjiaping Xintan Wangjiawan Qianjiangping Lianziya ( , Bp=13 m, Bt=22 days)

13 Fanjiaping landslide motion detected by SBAS The southern part of Fanjiaping landslide is very active. Deformation rate can reach 5cm/y. Time series deformation indicated Fanjiaping was moving during the whole period.

14 Part 2: Pixel offset tracking results

15 Fast moving landslides in Three Gorges 1000 Miao et al., Eng. Geology, 2014 InSAR Point-like targets offset tracking Underestimation on these landslides will happen with InSAR analyses. How to catch the deformation of the fast-moving landslides using highresolution SAR images?

16 Shuping Landslide (PS-InSAR) Active deformation observed in differential interferogram. Deformation rate estimated by PS-InSAR was unreasonably less than 1 cm/year. Underestimation happened with sparse PS points identified. Shuping landslide is a south-north oriented slope.

17 Point-like Targets - Corner Reflectors 14 CRs were identified on Shuping landslide. 4 CRs were installed outside Shuping landslide.

18 Point-like targets offset tracking (PTOT) Based on SAR image matching at subpixel-level accuracy Make use of pixels with high amplitude values Avoid noisy measurements in vegetated areas Without phase unwrapping Can measure displacements at centimeter-level accuracy in both line-of-sight direction (LOS) and azimuth directions * LOS vertical and east-west directions * Azimuth north-south direction Suitable for measuring large displacements. =>>> Hu, Wang &Liao, IEEE GRSL, 2014 Wang & Jonsson, IEEE JSTARS, In Press

19 Workflow of PTOT Time Series SAR Images PT Detection Offset Tracking Pixel Offset Extraction from Slave Images Master Selection Amplitude Correlation and PT Reselection Co-register Cull Points Common PTs Mean Amplitude Sinc Function Orbital Ramp Estimation - PT Candidates Time Series Deformation Mean amplitude image were used to select PT candidates. Common PTs were used in the final time series analysis.

20 Displacement at Shuping measured by HS data ( ) Azimuth (m) The displacement in azimuth and range directions can reach more than 0.8 meters and 0.6 meters respectively. Range (m) InSAR measurement significantly underestimated deformations in the LOS direction.

21 Displacement at Shuping measured by SM data ( ) Azimuth (m) The displacements in azimuth and range direction can reach more than 1 meter and 0.8 meters respectively. Observations coincide with the conclusions in Wang et al that the eastern part of Shuping landslide is more active. Range (m) Moving towards north direction into the Yangtze River.

22 Time series analysis Azimuth Water level decline VS displacement? Good agreement achieved on CR14 between HS and SM. Range BUT?

23 Comparison between HS and SM CR6-Azimuth Range CR15-Azimuth Range

24 Projection D sin sin D cos sin D cos d N E V D cos D sin d N E az az rg rg D N, D E, D V :displacements in the northing, easting and vertical directions. α and θ : heading angle and nominal incidence angle at the target point. d rg and d az : displacements measured in range and azimuth. δ rg and δ az : observation errors to be minimized.

25 Is it possible to combine HS and SM measurements? AX B ˆ T 1 T X ( A A) A B A sin sin cos sin cos HS HS cos sin 0 sin sin cos sin cos SM SM cos sin 0 HS HS HS HS HS SM SM SM SM SM X DN DE DV T B d d d d HS HS SM SM rg az rg az T

26 Typical Design matrix North East Vertical A HS SM Rang measurements by HS data is more sensitive to displacement in easting direction than that by SM data while the latter is more sensitive to vertical displacement.

27 Three dimensional displacement ( ) Horizontal Vertical

28 Summary InSAR and pixel offset method could be jointly used to more accurately map the landslides in TG. It is possible to derive 3D displacement from two descending orbit with different look angles.

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