Building health monitoring in the old town of Madrid: applicability of SAR Imagery to the monitoring of underground works through classification indexes

The old city centers of many major cities represent a great challenge from a constructive point of view since the foundations of the buildings consist of an aggregation of previous constructions. This endorses thorough monitoring activities during any underground construction. The capabilities of the persistent scatterer interferometry (PSI) can be exploited to cope with these monitoring needs. However, the old city centers represent a very challenging urban scenario since the rooftops are usually filled with air conditioning systems and due to the fact that the streets are usually crowded. This work assesses the applicability of the PSI technique under this challenging scenario. Moreover, it proposes a set of novel classification indexes that allow an objective assessment of the building's health and the impact derived from any activity. They can be applied in deformation monitoring and risk evaluation in urban areas. The applicability of the technique and the proposed indexes is validated in the monitoring of underground construction works in the old city center of Madrid comparing the results against on-ground measurements and identifying the potential and the limitation of the technique.