result evaluation of coherent target model product with...

DRAGON Programme (id:2567)

Result evaluation of Coherent Target Model Product with long-term InSAR

data set in Shanghai

LIESMARS

Mingsheng Liao, Yan WANG, Lijun LU, Deren LILIESMARS, Wuhan University

P. O. Box C310, 129 Luoyu Road, 430079, Wuhan, China

[email protected]

Zheng FANG, Zixin WE, Hanmei WANG, Lijun YANG, Ying LIUShanghai Institude of Geological Survey, Shanghai, China, 200072

November 29, 2005


Outline

• Background of our project• Subsidence in China• Overview of methodology• Preliminary result• Conclusion and remark


Project 2567, Dragon Programme

The scientific investigations of Project 2567, DRAGON Programme, focus on the applications of ESA data (ERS-1/2 and Envisat/ASAR) in TOPOGRAPHIC MEASUREMENT , include

•• Topographic mappingTopographic mapping

•• Land deformationLand deformation monitoring monitoring <=<= topic of this presentationtopic of this presentation


Prof. Deren Li Prof. Mingsheng Liao (Contact Point)

State Key Lab. For Information Engineering in Surveying, Mapping and Remote Sensing(LIESMARS) Wuhan University

Prof. Chao Wang Chinese Academy of Sciences

Prof. Agen Zhang Center for Land Subsidence of China Geological Survey

The partners in China


Prof. Fabio RoccaDipartimento di Elettronica ed Informazione

Politecnico di Milano, Italy

Dr. Alessandro FerrettiTele-Rilevamento Europa – T.R.E. s.r.l. Via Vittoria Colonna 7 20149 Milano, Italy

The partners in Europe


In China, land subsidence is one of the most urgent environmental dilemmas facing numerous megalopolises on which it is densely populated, thereby causing prominent damage.

Subsidence in China


Example: Subsidence History of Shanghai:

Reasonable adjusted the quality of water pump

Underground water over-pumped

3.5

87 (max.: 110)40

1972-1989 slightly subsidence

1957-1965 serious1949-1956 acceleration

Increase the quantity of water pumping and municipal engineering constructions

161990- now accretion

Reduced pumping and artificial intake of water

-31966-1971 rebound1966 – nowControl

subsidence

Underground water pumped241921-1948 development1921-1965Obvious

subsidence

Main causesAverage velocity (mm/y)

StagePeriod

Subsidence in China


Subsidence in China

• In Shanghai, Land subsidence is also a primary geologic disaster . Particularly with the developing of massive construction and increasing of groundwater mining, land subsidence had presented some new peculiarities in the past 15 years. It makes great effect on city planning、flooding prevention or municipal infrastructure.

• The ground network, such as optical leveling, GPS etc., is not enough for dynamic monitoring.

• InSAR should be of great benefit to understand the spatial and temporal distribution of land subsidence.

• Shanghai has been selected as main test site in our DRAGON project.


For limitations of traditional D-InSAR, the Permanent Scatterers technique has initiated by A. Ferretti and F. Rocca etc.

Point-wise targets are not affected by geometrical decorrelationSome pixels are only slightly affected by temporal decorrelationWe do look for reliable phase information on point target

Overview: methodology

∆φint = ∆φdef + ∆φgeom + ∆φtmp + ∆φtopo + ∆φnoise

Components of interferometric phase:

Point Target InSAR technique is applied for detecting long-term deformation in Shanghai test site.


Overview:Subsidence Monitoring in Shanghai, PS InSAR

Result of PS InSAR with ERS-1/2 derived by POLIMI and TRE

• 26 images (1993-2000) processed using PermanetScatterer technique;

• The velocity distribution in PSs has been compared with the subsidence map of Shanghai:

=>the results from InSAR and leveling are quite consistent.

---- (Report of Dragon Programme)


• The Coherent Target Analysis (CTA) provided an alternative approach to exploit the temporal and spatial characteristics of interferometric signatures of long-term InSAR data.• Coherent targets that includes targets that are temporarily coherent as well as targets with a low coherence. • CTA was adapted in Shanghai for cross validation of different approaches.

Overview: methodology


Features of Coherent Target Analysis

• Coherent Target Analysis methodology was said that not limited to a large number of scenes (Marco Van der Kooij, Fringe 2003).

• The temporal coherence is the main measurement of how stable the phase of a scatter is over time, not intensity stability index or averaging coherence .


Temporal Coherence

– Temporal coherence is used for measure of how stable the phase of a scatterers over time.

– Temporal Coherence of n Scenes of Interferogram is defined as

2 2

1 1( cos( )) ( sin( ))

n n

i ii i

n

φ φγ = =

+=

∑ ∑

• If φi does not change, the temporal coherence will be 1.


Criterion to Identify Coherent TargetExpected Temporal Coherence via the number of Interferograms

Recommended 4 sigma threshold: 0.91 for 10 scenes0.70 for 20 scenes0.44 for 50 scenes


• Coherent Target Analysis (CTA) with ERS-1/2 conducted by LIESMARS.

• 24 images (1993-2000) processed using Coherent Target Analysis method;

• SRTM DEM used as external DEM data set;

• The data processing chain for CTA is constructed based on a commercial InSAR software.

• The cross validation of results from CTA, PS and Leveling is working on.

Overview:Subsidence Monitoring in Shanghai, CTA


Preliminary result in Shanghai

Shanghai City Map

Developing urban area

Traditional urban area


Subsidence map from ground network(1990-1998)



SAR images

20661512000-12-5ERS2

1891-202000-6-13ERS2

18211622000-4-4ERS2

17862602000-2-29ERS2

17511142000-1-25ERS2

1716501999-12-21ERS2

1681981999-11-16ERS2

1611-3481999-9-7ERS2

15413501999-6-29ERS2

15063031999-5-25ERS2

11214491998-5-5ERS2

1086-661998-3-31ERS2

946-3101997-11-11ERS2

420-5541996-6-3ERS1

280-3851996-1-15ERS1

1754931995-10-2ERS1

70-1861995-6-19ERS1

001995-4-10ERS1

-513-701993-11-13ERS1

-5832411993-9-4ERS1

-6184501993-7-31ERS1

-653681993-6-26ERS1

-688811993-5-22ERS1

-7235491993-4-17ERS1

-9335001992-9-19ERS1

BtBnDateSensor

85 Km

85 K

m

25 scenes ERS-1/2 SAR images from 1992-2000



Main steps in CTA Processing

• Generation of interferograms (including flat earth phase and topographic phase removal) • Atmospheric correction (constant phase) • Phase modification based upon DEM elevation • Calculation of temporal coherence adjusted for atmospheric and DEM error • Deformation estimate for each pixel with the “template search”; • Final output map (geocoded or slant-range) and reporting products

- average backscatter- temporal coherence- DEM error - deformation map


Criterion to Identify Coherent Target

For 24 scences of interferograms , the temporal coherence is expected to be higher than 0.7


Master image

24 scenes of interferogram created


interferogram

temporal coherence

atmospheric offset

coherent point targets

Average backscatter image



Validation of point target


Example:Hero’s Monument is diamond-shaped stable scatterer, a landmark built up during 1988-1994.


………0.84 -22.90 20 0.79 -18.35 10

0.78 -26.66 29 0.76 -22.90 19 0.80 -34.99 9

0.78 -26.67 28 0.79 -24.36 18 0.85 -39.52 8

0.75 -27.42 27 0.75 -29.68 17 0.75 -38.76 7

0.77 -28.18 26 0.79 -28.16 16 0.76 -40.28 6

0.75 -28.18 25 0.80 -28.16 15 0.79 -13.82 5

0.77 -26.67 24 0.81 -28.17 14 0.75 -44.81 4

0.78 -28.94 23 0.76 -27.41 13 0.76 -23.62 3

0.75 -47.07 22 0.77 -27.41 12 0.76 -22.11 2

0.76 -19.10 21 0.85 -27.41 11 0.75 -19.09 1

CoherenceCT Vel.(mm/y)No.Coherenc

eCT Vel.(mm/y)No.CoherenceCT Vel.

(mm/y)No.


Subsidence velocity and temporal coherence on part of coherent targets


Benchmark

Reference point

CTs

Distribution of benchmarks and CTs in the test site



Comparison of subsidence velocities, coherent target via benchmark

-- Nearest neighboring Coherent Target with benchmark

Validation of the results (1)

Benchmark

< 100m

Nearest CT


Average：－1.0406 mm/y STDEV： 6.576682 mm/y

14.21 -17.75 -31.96 16

1.64 -11.38 -13.01 15

10.20 -6.63 -16.83 14

-3.22 -43.50 -40.29 13

-6.69 -21.25 -14.56 12

-10.94 -39.13 -28.18 11

0.01 -25.88 -25.89 10

-7.53 -30.38 -22.85 9

-4.81 -23.88 -19.07 8

1.93 -13.38 -15.30 7

-6.57 -35.50 -28.93 6

-6.29 -21.63 -15.33 5

1.60 -14.50 -16.10 4

-2.61 -17.88 -15.27 3

-0.23 -14.75 -14.52 2

2.64 -11.13 -13.77 1

Difference (mm/y)Leveling (mm/y)CTs (mm/y)No.

min. difference

max. difference




Comparison of subsidence velocities between CTs and benchmarks-- Nearest neighbor with benchmarks


Discussions

•The distribution tendency of subsidence from CTA method is consistent with the leveling data in benchmarks.

• Few coherent targets with large bias exist in preliminary result.

• According to the preliminary validation, temporal coherence can be introduced as a measurement for selection of stable point target.

• The further investigation and field survey should be carried out later to explore the characteristics of point target and improve the accuracy.


Conclusion & Remark (1)

• The ERS-1/2 image stack covering the test area, Shanghai between 1992 and 2000 were chosen and processed with Coherent Target Analysis.

• The product based on the Coherent Target Analysis is compared with ground leveling data.

•The preliminary result is promising but expected to be investigated in more detail.


Conclusion & Remark (2)

• In many coastal cities in China like Shanghai, there are a lot of new constructions on soft clay ground. The problem of ground stability appears obviously.

• Up to now the mechanism of the soft clay ground stability has not been comprehensively known because of the lack of the systematic monitoring and the accumulated data.

• InSAR technique should be a potential technique in urban environment research.

• And plenty of historic archive and new arrival SAR dataset from ESA should benefit to monitoring subsidence in these cities.


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