An Application of Interferometric Synthetic Aperture Radar in a Railroad Corridor

El Hachemi Bouali, Thomas Oommen, Rüdiger Escobar-Wolf, Samuel Douglas,

Vicky Hsiao, Adrian Bohane

14th Annual Technical Forum for Geohazards Impacting Transportation in the Appalachian Region Geohazards Session 4: Geophysical, Geotechnical Techniques & Instrumentation (August 6, 2014)

DISCLAIMER: The views, opinions, findings, and conclusions reflected in this presentation are the responsibility of the authors only and do not represent the official policy or position of the USDOT/OST-R, or any State or other entity.

Discussion Outline

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I. Introduction to project goal

II. Interferometric Synthetic Aperture Radar (InSAR)

III. Railroad Corridor Setting Local Geology History of Slope Movements Observed in the Field

IV. InSAR Data & Results Two Pass Interferometry Persistent Scatterer Interferometry SqueeSAR™

V. Conclusions

Project Goal

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Establish a economically sustainable framework for managing geotechnical assets using remote sensing along the transportation corridor.

What are Geotechnical Assets?

4 Image source: Vessely (2013)

Performance and safety of the transportation infrastructure throughout the life-cycle depends upon the geotechnical asset that

is adjacent to it or that supports it.

Geotechnical Assets

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Proposed Geotechnical Asset Taxonomy (Anderson and Schaefer, 2014)

This study will focus on the independent features

Transportation Asset Management

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Introduction to InSAR

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Synthetic Aperture Radar: A coherent, mostly airborne or spaceborne, side-looking radar system. It utilizes the flight path of an attached platform to create a synthetic aperture, or ‘fake antenna.’ Interferometric SAR: The use of multiple acquired SAR images as a method for change detection measurement.

ESA, 2002

Introduction to InSAR

Tx = transmission location Rx = reception location

L Tx Rx

∆d

Time 1 Time 2

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Satellite actually measures: 1. Amplitude of radar wave 2. Phase of radar wave

Ground Surface

Bouali, 2013

Introduction to InSAR

The importance of phase:

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θ

Period = 2π = λ

Bouali, 2013

Railroad Corridor: Geography & Geology

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Located in the mountainous terrain of SE Nevada

Tvtw Tvt Tvy Railroad

Siding

Main Scarp

70°

65°

SW NE

Tvtw: Rhyolitic Welded Tuff and Breccia

Tvt: Tuff and Tuffaceous Sediments

Tvy: Volcanic Rocks, Undivided Slope Height ≅ 275 feet

Railroad Corridor: Field Observations of Slope Movement

Timeline

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Dec. 2005: Slope movements began

Feb. 2006: Rotational slope

motions observed

May 2011: Massive rock slides began

2011-present: Detailed ground

observations May 18-22, 2014 Field Observations

InSAR Data

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40 ERS-1/-2 SAR Images (1992-2000) 40-50 ENVISAT ASAR Images (2003-2010)

Level 1 Single-Look Complex Images

In-Phase (real) – Amplitude (A) Quadrature (imaginary) – Phase (θ): [0, 2π]

Descending Scenes

Line-of-Sight: 23° from vertical in NW-direction

SRTM Digital Elevation Model

InSAR Results: Techniques

2-Pass Interferometry Interferometric Stacking

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Uses a pair of SLC images as input

Creates one interferogram

Coherence Threshold γ = 0.25

Requires a stack of N number of SLC images

Creates N-1 interferograms

γ = 0.70

InSAR Results: Two Pass

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Coherence

October 10, 2004 – December 19, 2004

N

December 19, 2004 – January 23, 2005 January 23, 2005 – February 27, 2005 February 27, 2005 – April 3, 2005 April 3, 2005 – May 8, 2005 May 8, 2005 – June 12, 2005 June 12, 2005 – July 17, 2005 July 17, 2005 – August 21, 2005 August 21, 2005 – September 25, 2005

1 kilometer

Red = 1 Blue = 0

October 10, 2004 – December 19, 2004

InSAR Results: Two Pass

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Line of Sight (LOS) Displacement

N

1 kilometer

December 19, 2004 – January 23, 2005 January 23, 2005 – February 27, 2005 February 27, 2005 – April 3, 2005 April 3, 2005 – May 8, 2005 May 8, 2005 – June 12, 2005 June 12, 2005 – July 17, 2005 July 17, 2005 – August 21, 2005 August 21, 2005 – September 25, 2005

LOS Direction

(meters)

positive = uplift negative = subsidence

InSAR Results: Persistent Scatterer Interferometry

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-50-40-30-20-10

010203040509/1/2002 1/14/2004 5/28/2005 10/10/2006 2/22/2008 7/6/2009 11/18/2010

Tot

al D

ispl

acem

ent

(mm

)

Date

-120

-100

-80

-60

-40

-20

0

20

409/1/2002 1/14/2004 5/28/2005 10/10/2006 2/22/2008 7/6/2009 11/18/2010

Tot

al D

ispl

acem

ent

(mm

)

Date

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InSAR Results: Persistent Scatterer Interferometry

0

20

40

60

80

100

120

140

160

1809/1/2002 1/14/2004 5/28/2005 10/10/2006 2/22/2008 7/6/2009 11/18/2010

Tot

al D

ispl

acem

ent

(mm

)

Date

0

10

20

30

40

50

60

70

80

909/1/2002 1/14/2004 5/28/2005 10/10/2006 2/22/2008 7/6/2009 11/18/2010

Tot

al D

ispl

acem

ent

(mm

)

Date

InSAR Results: SqueeSAR™

18 © TRE 2014 www.trecanada.com

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Richmond Slide

© TRE 2014 www.trecanada.com

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Richmond Slide

© TRE 2014 www.trecanada.com

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Richmond Slide

© TRE 2014 www.trecanada.com

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Richmond Slide

© TRE 2014 www.trecanada.com

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Richmond Slide

© TRE 2014 www.trecanada.com

Application: Searching for Additional Slope Instability

24 © TRE 2014 www.trecanada.com

Able to search for additional

areas of ground movement

along railroad corridor.

Conclusions: Results Comparison

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Two-Pass Interferometry PSI SqueeSAR™

Advantage Location of ground

movements and coherence variation

Velocity of stable points

Utilizes persistent and distributed

scatterers

Limitation Velocity

measurement prone to error

Does not work well in rural areas

Performs better than PSI, but still

limited capabilities in rural areas

SNR Ratio

Uplift Magnitude (mm) n/a 40-160* 20-40*

Subsidence Magnitude (mm) n/a 40-100* 40-70*

*Points do not overlap

Conclusions

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Advantages of radar interferometry Cost effective

Covers large area Data generally free (with written proposal)

Requires less time than separate field excursions Wealth of historical data (1992-present, depending on satellite)

Limitations of techniques Range of displacement rates (order of magnitude) Point locations unknown prior to processing

Different techniques yield different point locations Complex topography = paucity of points Velocities limited to LOS direction

Acknowledgements

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• USDOT- Office of the Assistant Secretary for Research and Technology Program Manager: Caesar Singh Cooperative Agreement #RITARS-14-H-MTU Project: Sustainable Geotechnical Asset Management

along the Transportation Infrastructure Environment Using Remote Sensing

Data provided by the European Space Agency DEM provided by the Jet Propulsion Laboratory at

California Institute of Technology

Any Questions? Thank You!

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