Objectives  Thanks to the data open access policy of European Space Agency, it has become easy to acquire long time series dual polarimetric Sentinel-1 data over the most of the world's big cities. The use of dual polarimetric Sentinel-1 data is expected to produce better urban ground deformation monitoring results than single polarimetric data, however, there are few studies about this topic. To this end, based on the long time series single and dual polarimetric Sentinel-1 data, this study employs persistent scatterer interferometry (PSI) and polarimetric persistent scatterer interferometry (PolPSI) to monitor the recent ground deformation of the Mexico City in United Mexican States and Beijing City in China, respectively.

  Methods  For the interferograms' polarimetric optimization of PolPSI technique, the exhaustive search polarimetric optimization (ESPO) meth‍od has been used, and the dispersion of amplitude (DA) is taken as the interferometric phase quality criteria. After the polarimetric optimization, for the PolPSI technique, the optimized interferograms are then employed for ground deformation monitoring through PSI processing over the two study areas. The StaMPS algorithm has been employed for the PSI processing for both single and dual polarimetric Sentinel‍-‍1 data sets.

  Results  The results show that, after the polarimetric optimization with dual polarimetric Sentinel-1 data, the phase quality of the interferograms is improved and the proportion of high quality pix‍els is significantly increased. There is a significant increase in high quality pixel after using dual polarimetric data with respect to that of single polarimetric data for ground deformation monitoring. Specifically, the qualified pixels' density has been increased by 88% and 50% for Mexico City and Beijing City, respectively. Moreover, due to the higher pixel density, the obtained ground deformation monitoring results of some sub‍areas are more reliable by using dual polarimetric data.

  Conclusion  This study demonstrates that higher density and better reliability of the qualified pixels can be obtained by using Sentinel-1 dual polarimetric data for urban ground deformation monitoring.