2/4/2014

CEReS, Chiba University

Monitoring glacier flow velocity by sar interferometry andtexture tracking method using alos palsar dataaroundmt. Everest region

Presented by:
Nikhil Raj Poudyal
Center for Environmental Remote Sensing (CEReS)
Tateishi LAB
Chiba University

Supervisor:
Tateishi Ryutaro
Professor (CEReS)
Chiba UniversityJapan1

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Presentation Outline
 Background & Introduction
 Real Case Scenario Objectives
 Data Methodology
 Khangshung Glacier Result & discussion
 Khumbu Glacier Result & discussion
 Discussions
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1. Background & Introduction• Why to study the Glaciers ?
• Glaciers need to be studied for variety ofpurposes including– to track climatic variations– effects on hydrology– sea level rise– hazard assessment• Glacier Lake Outburst Flood (GLOF)
Reference: WWF Nepal Program March,2005 report
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1. Background & Introduction• The monitoring of temperate glacier that is fast evolving• As an indicator of the local effects of global climate change• Regular observations of glacier activity and to provide dense
measurements of physical parameters• Disastrous flood prediction, prevention adaptive measures wellbefore occurrence• By doing this, it is expected that the extent of the damage of the
populated area or infrastructure can be greatly controlled• Understanding the response of glaciers and glacial lakes with theglobal rising temperature is an essential aspect of planning water
resources as well as managing the potential for GLOF disasters

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1. Background & Introduction
Geography of Nepal••

Shaped roughly like a rectangle with China to the north and India on threeother sides
Nepal is situated between latitudes of 26022' to 30027' north and between
longitudes of 8004' to 88012' east

800 kmReference:
WWF Nepal
ProgramMarch,2005
report140 kmCEReS, Chiba University3

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2. Real Case Scenario
Glacial Lake Outburst Flood (GLOF)••

A GLOF is characterized by asudden release of a hugeamount of lake water thatrushes along the stream
channel downstream in theform of dangerous floodwaves.
Devastating consequences fordown hill communities,hydropower stations andother infrastructure.

Reference:
http://academic.emporia.edu/aberjame/student/dahms4/web1.htm

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2. Real Case Scenario
Glacial Lake Outburst Flood (GLOF)

Reference: WWF Nepal Program March,2005 report
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2. Real Case Scenario
Glacial Lake Outburst Flood (GLOF)•The Dig Tsho GLOF: The site of Namche
Hydropower Project destroyed by the
GLOF on 4 August 1985 (left)•The lake in 2004 (bottom)(Source: WWF Nepal Program)

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3. Objectives on the Horizon• Use of ALOS PALSAR Data to– Analyze the movement of the Ice surface (moving temperate glaciersmade of ice, snow and rocks)– Detecting the change in the size of Glacial Lake

• Creating Digital Elevation Model (DEM)– Is widely used for flood prediction and estimating the affected area
(Disaster mitigation planning)– It is possible to detect the temporal changes of glacial lakes, glaciersand moraines by comparing two DEMs produced at two different timeintervals

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3.1 Current objectives• Use of ALOS PALSAR Data to– Analyze the velocity rate for Khangshung and Khumbu
Glacier (moving temperate glaciers made of ice, snow androcks)• By using DInSAR technique

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4. Data
ALOS PALSAR (Synthetic Aperture Radar) Fine Mode

Pair 1Pair 2Satellite

Sensor

ProcessLevel

Off Nadir
Angle

Observation
Date

ALOS

PALSAR

1.03402007/12/13

ALOS

PALSAR

1.03402008/1/28

ALOS

PALSAR

1.03402009/11/2

ALOS

PALSAR

1.03402009/12/18

Repeatpass
periodPerpendicular
Baseline (m)46 Days280

46 Days212

FrameCenter
NumberPasses540

Ascending

540

Ascending

540

Ascending

540

Ascending

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5. InSAR & DInSAR Methodology
2 DATA SETALOS PALSARLEVEL 1.0
DATA

PHASE
UNWRAPPINGREFINEMENT AND
REFLATTENING

Focusing & Baseline
Estimation

SLCImage 1

SLCImage 2•co registered•multi-looked• master Intensity•slave Intensity

OrbitalRefinement
GCP

PHASE TO HEIGHTPHASE TO DISPLACEMENT &GEO-CODING (DEM Generation)
PRODUCTSVarious Interferogram
Various Displacement MAP
Various DEM

Downloaded
SRTM4 DEM

Modeling&Analyzing

Interferogram
Generation &Flattening
Adaptive Filter &Coherence
Generation CEReS, Chiba University

Process: Focusing & Baseline Estimation••

The SAR signal energy reflected from one single point isspread along both azimuth and range direction
The purpose of SAR focusing is to collect this dispersed
energy into a single pixel

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Process:
Co registered + Multi looked
Master Intensity & slave Intensity

2007-12-13

2008-01-28

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Process: Interferogram Generation• The distance difference between a point on
the Earth and the sensor position on the twoacquisitions can be measured by the phasedifference (ϕ) between two complex
coregistered SAR images.
• This is performed by multiplying one imageby (the complex conjugate of) the other one,
where an interferogram is formed.
• The phase of the interferogram contains
fringes that trace the topography (or thedisplacement) like contour lines.

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Process: Interferogram Flattening•

If a reference Digital Elevation Model is entered as input
the Flattening process is executed by removing theavailable topography.
•The better the reference Digital Elevation Modelaccuracy/resolution the better the result in terms oftopography removal.
•The Figure illustrates the interferogram flattened byconsidering a Digital Elevation Model (SRTM4), i.e. thetopography.
•If this is compared to the initial interferogram, it isevident that the number of fringes has been strongly
reduced, hence facilitating the phase unwrapping
process and the generation of the Digital Elevation
Model or, in case of differential interferometry, themeasurements of ground motions.
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Process: REFINEMENT AND REFLATTENING• This step is crucial for a correct transformation of the unwrapped phase information into height (ordisplacement) values.
• It allows both to refine the orbits (i.e. correcting possible inaccuracies) and to calculate the phaseoffset (i.e. getting the absolute phase values), or remove possible phase ramps.
• The execution of this step is mandatory for Digital Elevation Model generation as well as for
Displacement Mapping.
• To execute this step a Ground Control Point file must be previously created.

Un-Refined Interferogram(Before)CEReS, Chiba University

Refined Interferogram(After)10

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Process: Adaptive Filter & Coherence Generation• Given two co-registered complex SAR images (S1 and S2),
one calculates the interferometric coherence (g) as a ratio
between coherent and incoherent summations• The observed coherence - which ranges between 0 and 1 is, in primis, a function of systemic spatial decorrelation,
the additive noise, and the scene decorrelation that takes
place between the two acquisitions.
• In essence coherence has, in primis, a twofold purpose:––

To determine the quality of the measurement (i.e.
interferometric phase). Usually, phases having coherence
values lower than 0.2 should not be considered for thefurther processing.
To extract thematic information about the object on theground in combination with the backscattering coefficient(σ0).

• The Figure illustrates the estimated coherence• Bright values correspond to values approaching to 1, whiledark values (black = 0) are those areas where changes (orno radar return, radar facing slope, etc.) occurred during
the time interval, 48 days in this case.

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Process: Phase Unwrapping• The phase of the interferogram can only be modulo 2π• Hence anytime the phase change becomes larger than 2π thephase starts again and the cycle repeats itself.
• Phase Unwrapping is the process that resolves this 2π
ambiguity.
• Several algorithms (such as the branch-cuts, region growing,minimum cost flow, minimum least squares, multi-baseline,etc.) have been developed; in essence, none of these is perfectand different or combined approaches should be applied on acase by case basis to get optimal results.

• The Figure illustrates the unwrapped phase.
• At this stage the grey levels representing the phase
information are relative and must be absolutelycalibrated in order to convert it to terrain height

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Process: PHASE TO HEIGHT & GEO-CODING (DEM Generation)• The unwrapped phase is recombined with the synthetic phase and is converted to elevation andgeocoded into a specified map projection.
• This step is performed in a similar way as in the geocoding procedure, by considering the Rangeoppler approach and the related geodetic and cartographic transforms.

Generated DEM
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7. Study Site in SAR Intensity (Amplitude) ImageCEReS, Chiba University

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Khangshung Result & Discussion

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Khumbu Result & Discussion

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8. Discussion• InSAR is considered for giving high level of accuracy if perfectimage (good baseline, high coherrence, lower period ofrepeat pass) is selected for the process• Other Satellite data are most welcome• Both Ascending and Descending satellite data to bring out
more accurate measurement specially in case of North-Southflow• It is somehow difficult to obtain good coherence in stiff slopes
and terrain area so Amplitude tracking could also berecommended• More to do in Future…

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