Quantitative and Qualitative Analysis of Coherence in Multi-temporal SAR Interferometry

Post-doctoral Scholar, PhD, Falah Fakhri

Department of Geography and Geology, University of Turku, F1-20014 Turku, Finland. Email: falah.fakhri@utu.fi

Abstract Coherence has become a valuable and common indicator of interpolating and manipulating many processes and studies of SAR Interferometry (InSAR). Land use and land cover varieties are considered the main

vital influences and controllers of the coherence conduct. Seven interferometrics coherences are here generated and compared according to the differences in perpendicular (B┴) and temporal baselines using 14 C-

band European Remote Sensing (ERS)-1/2 synthetic aperture radar SAR Single Look Complex (SLC) VV-polarization images acquired in ascending mode during 1995 – 1999 over the northern east of Thessaly

plain. The result shows significant and remarkable impact of B┴ and temporal baseline on coherence which is ranged between 0.42 and 0.49. Also land use and land cover dynamics play imperative roles on the

behavior of SAR inferometric coherence.

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Turun yliopisto – Suomi

University of Turku, Department of Geography and Geology – Turku – Finland, NOV. 2013- Feb. 2015

Figure 2. Soil order map at the northern part of Larissa base on SLC SAR image.

Study area

GREECE

Larissa

Figure The location of the study area at the north-

eastern part of Thessaly (red circle).

2- SAR data and Processing The data used in this study consists of 14 Single Look Complex (SLC) SAR C-band images of ERS- 1/2 ascending mode during the years 1995 and 1999. 7 coherence interferograms

have been generated according the differences of (B┴) and temporal baselines.

InSAR- processing was performed by using Gamma Remote Sensing (S/W). 7 -look intensity images. Common- band filtering was performed before interferogram generation to reduce

baseline- de-correlation. The InSAR coherence of all the pairs was estimated using the first results of interferogram coherence for the reason that the second interferogram coherence

result is an adaptive coherence and consequently, it might not provide the real value of coherence magnitude (Fakhri, 2013).

Material and methods

1- Study Area

The study area is located in the Eastern part

of northern Thessaly region in Central

Greece. This part of Greece is characterized

by basin can be subdivided by a group of

hills into two sub-basins, the western and

the eastern (Rozos et. al. 2010). These sub-

basins constitute the area’s two main

hydrogeological units which also develop

significant aquifers. Overexploitation of

these aquifers has led to claims of land

damage by subsidence.

Conclusions

The result of this study has demonstrated the significant and remarkable impact of temporal and B┴ baselines on coherence behavior. Additionally the involvements of land use and land cover are playing a vital influence role

on coherence variations. Long B┴ causes change in the look angle of different backscattering characteristics thus leads to low coherence. It is worth mentioning that the coherence within urban area is less affected by the long

temporal baseline span. However it is more influenced by long B┴ particularly in the area of low scatterers distribution. The value of R2 indicates to low linear correlation strength between the two variables temporal and B┴

baselines.

Figure a, b, c, d, e, and f are depicted the variation in coherence with temporal and B┴ baselines

Figure g, h, and i are depicted the variation in coherence with temporal and B┴ baselines

Figure Location map of the study area, explaining Multi-look average SAR image ascending track

Figure distribution of both temporal and B┴ baselines of generated interferometric pairs

Figure the correlation of mean coherence to a the B┴ and b to the temporal baseline