Monitoring Mosul Dam Through Low And High-Resolution SAR Data

Structural health assessment is an important practice to guarantee the safety of infrastructure in general. In case of dam monitoring, it is necessary to control the structure itself and the water reservoir, to guarantee efficient operation and safety of surrounding areas. Ensuring the longevity of the structure requires the timely detection of any behaviour that could deteriorate the dam and potentially result in its shutdown or failure. Traditional structural dam monitoring requires the identification of soil movements, tilt, displacements, stress and strain behaviour. The detection and monitoring of surface displacements is increasingly performed through the analysis of satellite Synthetic Aperture Radar (SAR) data, thanks to the non-invasiveness of their acquisition, the possibility to cover large areas in a short time and the new space missions equipped with high spatial resolution sensors. The availability of SAR satellite acquisitions from the early 1990s enables to reconstruct the historical evolution of dam behaviour, defining its key parameters, possibly from its construction to the present. Furthermore, the progress on SAR Interferometry (InSAR) techniques through the development of Differential InSAR (DInSAR) and Advanced stacking techniques (A-DInSAR) allows to obtain accurate velocity maps and displacement time-series. The importance of these techniques emerges when environmental or logistic conditions do not allow to monitor dams applying the traditional geodetic techniques. In such cases, A-DInSAR constitutes a reliable diagnostic tool of dam structural health to avoid any extraordinary failure that may lead to loss of lives. In this contest, an emblematic case will be analysed as test case: the Mosul Dam, the largest Iraqi dam, where monitoring and maintaining are impeded for political controversy, causing possible risks for the population security. In fact, it is considered one of the most dangerous dams in the world because of the erosion of the gypsum rock at the basement and the difficult interventions due to security problems. The dam consists of 113 m tall and 3.4 km long earth-fill embankment-type, with a clay core, and it was completed in 1984. It started generating power on 1986. Specific objective consists in determining the degree of detail of dam surface strains that can be obtained from different satellite SAR datasets at different resolutions (microwaves X and C bands). Therefore, different datasets are analysed: the archive available SAR data (ERS and Envisat from ESA), the currently acquiring Sentinel data (EU Copernicus programme) and the high-resolution COSMO-SkyMed data (ASI program) over the study area (Mosul dam). The different stacks of data are processed applying SBAS and PS A-DInSAR techniques; the deformation fields obtained from SAR data are evaluated to assess the temporal evolution of the strains affecting the structure. Obtained results represent the preliminary stage of a multidisciplinary project, finalized to assess possible damages affecting a dam through remote sensing and civil engineering surveys.