Potential of advanced SAR interferometric techniques of the new generation C-band Sentinel-1 SAR mission

Spaceborne synthetic aperture radar (SAR) Interferometry (InSAR) provides a unique tool for mapping the spatial and temporal evolution of surface displacement and deformation over large areas. In particular, InSAR introduces an advantage over other geodetic methods that it constitutes a denser and thus more revealing source of information for geophysical processes. InSAR basic principles and applications have been well documented throughout the years, InSAR techniques have been enhanced and respective commercial, as well as open-source, software has been developed. The Persistent Scatterers (PS) radar interferometry method focuses on the identification of coherent scatterers in a series of interferograms for measuring surface displacement of the order of a few millimetres. Using PS, long time series of data (e.g. 10–15 years) can be processed with fewer restrictions regarding the selected baselines and with the potential of using baselines close to the critical value. On the other hand, the small baseline subset (SBAS) technique is a time series analysis approach which uses small baseline values (usually <250 m) in order to minimize decorrelation. With ERS-2 and Envisat satellites taken out of service in September 2011 and April 2012, respectively, an era of very successful European Space Agency (ESA) C-band SAR missions came to an end. Nevertheless, the ERS/SAR and Envisat/ASAR acquisitions archived over the past 20 years comprise a particularly consistent, long time series data set suitable for implementing PS and SBAS interferometry. Currently, within the new European endeavour of the Copernicus Programme (formerly Global Monitoring for Environment and Security/GMES), the Sentinel-1A satellite has been in orbit since April 2014. With a revisit time of 12 days (Envisat/ASAR had a revisit time of 35 days), Sentinel-1A will compile a new set of C-band SAR observations. Given the established importance of InSAR applications, the SAR sensor on board Sentinel-1A has a new dedicated mode for InSAR measurement, i.e. the interferometric wide swath mode (IW). These characteristics of the Sentinel-1 mission highlight its importance, especially in the field of surface displacement analysis with multitemporal InSAR techniques. The above mentioned advanced techniques are also very relevant to the new radiometric calibration technique to be systematically applied to Sentinel-1 data. Radiometric calibration of SAR products is crucial for various applications, as its successful completion allows the accurate exploitation of the radar backscatter coefficient. The objective of this type of calibration is to provide SAR imagery in which the pixel values can be directly linked to the radar backscatter. This is usually achieved through an internal calibration scheme that monitors the acquisition system, as well as external calibration using terrestrial targets. Such targets may be corner reflectors and/or transponders, which can be costly and difficult to install. Exploiting InSAR/PS for Sentinel-1 calibration purposes will render the installation of expensive equipment obsolete, while ensuring the required radiometric quality of the acquired images. In the frame of this thesis two test sites have been observed: Etna volcano and Thessaloniki (Greece) urban area. The above mentioned techniques have been used for Etna lava flows detection and classification of the age of the lava. The number of PS and coherent points varies according to different type and age of volcano emitted products the results obtained were also compared with a lava classification map obtained from Sentinel-2 simulated data. PS interferometry and Small Baseline (using both ERS SAR and Envisat ASAR images) have also been used to detect and monitor subsidence phenomena due to tectonic movement in the west part of city of Thessaloniki (Greece). All the results obtained so far are meant to be put in the frame of the prevision of the performance of the new ESA SAR Sentinel-1. In particular the results of the simulated PS calibration module (which will be systematically operative after the launch of the satellite) has been analysed and its output will be used for further analysis. The PS calibration module use as input the PS map obtained from a stack of data and produce as output the calibration (external calibration) constants form each PS. Finally the first interferometric results with Sentinel-1 (both for topographic and deformation applications) have been produced and showed. In addition a simulation of Sentinel-1 amplitude data using Radarsat-2 together with speckle tracking technique results over Viedma glacier (Argentina) is presented as a complement of this work.