Seasonal tropospheric oscillations observed in InSAR time series

Abstract

Applying the Multidimensional Small Baseline Subset Interferometric Synthetic Aperture Radar (MSBAS InSAR) algorithm to 250 ENVISAT and RADARSAT-2 SAR images spanning 2003-2013 we computed time series of ground deformation over Naples Bay Area in Italy. Two active volcanoes, Vesuvius and Campi Flegrei, are located in this area in close proximity to a densely populated city of Naples. For the first time with a remarkable clarity in the vertical component of time series we observed elevation dependent seasonal oscillations with an amplitude of up to 1.5 cm, substantially larger than the longterm annual deformation rate. Analysis, utilizing ground weather station and radiosonde data, linked observed oscillations with seasonal fluctuations of water vapor, air pressure and temperature in a lower troposphere. Atmospherically corrected time series confirmed continuing subsidence at Vesuvius previously observed by GPS and levelling techniques. Developed methodology demonstrated that for spatially localized studies the Atmospheric Path Delay (APD) can be successfully modeled as an elevation dependent seasonally oscillating signal.