Capability of X-Band Persistent Scatterer Interferometry to Monitor Land Subsidence in the Venice Lagoon

Land subsidence is a widespread phenomenon, particularly relevant to natural areas such as wetlands, deltas, and lagoons characterized by low elevation with respect to the mean sea level. The possibility of mapping vertical displacements of large coastal lowlying areas at very high resolution began in the 2000s with the development of the Persistent Scatterer Interferometry (PSI). This synthetic aperture radar (SAR)-based methodology detects the displacements of man-made structures within the landscape, such as buildings, utility poles, and roadways. Experience with SAR data of the European Remote Sensing satellites ERS-1, ERS-2, and ENVISAT, characterized by a spatial resolution of about 20 m, a wavelength lambda of the signal of 5.66 cm (C-band), and a repeat cycle of 35 days, suggested that persistent targets can be identified only for a fraction of the number of buildings or infrastructures larger than a few meters, and the precise position of the SAR scatterers are difficult to discern. With a very-high image resolution (about 3 m) and an acquisition repeatability never available in the past (between 11 and 16 days), the new generation of X-band (lambda = 3.11 cm) SAR satellites has improved significantly the possibility of monitoring the movements of single small structures scattered within rural and natural environments. In this work, we present the PSI outcome in the Venice Lagoon using the German TerraSAR-X and the Italian COSMO-SkyMed satellites. The investigated period covers the time interval 2008-2011. The outcomes of the two X-band analyses are compared both at the regional and the local scale in terms of target coverage and distribution and subsidence rates.