The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
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InSAR range changes in the LOS direction decreased from 9.9 
mm before correction to 4.1 mm after correction. It is also 
shown that the integration of InSAR time series and MERIS 
water vapour correction model (i.e. InSAR TS + PWV) is 
promising for mapping small deformation signals: (1) it has the 
ability to map surface deformation as it evolves in time; and (2) 
it is able to separate deformation signals from water vapour 
effects without requiring a priori deformation model, which is 
the key advantage of the InSAR TS + PWV approach. 
It should be noted that MERIS near IR water vapour products 
are usable only under cloud-free conditions and 2 ASAR 
images were excluded in this study due to the presence of 
clouds. Therefore, the temporal resolution (or sampling rate) of 
the retrieved deformation time series decreased to some extent, 
indicating that water vapour data availability is a limitation of 
the InSAR TS + PWV approach. Since Numerical Weather 
Models (NWM) can provide estimates of tropospheric path 
delays with a global coverage, 24 hours a day in all weather, it 
is likely that the use of NWM will expand the application of the 
InSAR TS + PWV approach for deformation mapping, which 
will be an important issue in future work. 
ACKNOWLEDGEMENTS 
This work has been carried out within the NERC COMET. The 
author is greatly indebted to Eric J. Fielding (JPL), Paul Cross, 
Ian Dowman and Ant Sibthorpe (UCL) for their continuous 
support and fundamental help during this study. The ENVISAT 
ASAR and MERIS data are copyrighted by ESA and were 
provided under projects AOE.668 and Cl P.3336. 
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