Integration of GNSS and Satellite InSAR Data: Derivation of Fine-Scale Vertical Surface Motion Maps of Po Plain, Northern Apennines, and Southern Alps, Italy

Global Navigation Satellite System (GNSS) and satellite synthetic aperture radar (SAR) interferometry represent the most important space geodetic techniques usually exploited to measure millimetric ground deformation on earth surface at both local and wide-area scale. SAR images processed with persistent scatterers interferometry (PSI) multitemporal approach lack of an absolute reference datum. In this paper, SAR images are calibrated with data derived from permanent GNSS stations, in order to obtain absolute and more accurate displacement values. The method used to correct PSI with GNSS is based on existing methodologies commonly applied in the geodetic practice of combining crustal and local deformation studies with geospatial statistical analysis. The spatial distribution of vertical terrain defiwmations and their temporal changes are coherently measured, leading to a fine-scale surface velocity map in the central-eastern Po Plain, Northern Apennines, and Southern Alps in Italy. The results reveal significant subsidence rates on the north-western Adriatic coast including the Po Delta and the lagoon of Venice, as well as on Bologna and Ferrara cities in agreement with long-term displacement motion values provided by geological data and other previous works performed at local scale. This paper demonstrates the importance and effectiveness in creating a single, unique surface motion map by merging different data sets in which geodesy plays a relevant role in the datum alignment of PSI products before the stacking of the SAR maps.