Operation of Interferometric SBAS-DInSAR Data for Remote Structural Monitoring of Existing Bridges

Several recent studies have investigated the opportunities of differential interferometry synthetic aperture radar (DInSAR) using satellite data for structural health monitoring (SHM) of civil structures. However, its use in structural engineering is still debated because of the lack of a general understanding of the potential and limitations of the technology for bridge SHM. To overcome this issue, specific methods of data processing and displacement assessment with error quantification need to be developed. The present paper aims at giving an insight into the use of small baseline subset-differential synthetic aperture radar interferometry (SBAS-DInSAR) as a remote-sensing technology for civil infrastructure monitoring combining information at a large scale with those associated with a single bridge. In particular, an operational framework for the selection and processing of a measurement time series representative of the structural behavior of the bridge of interest is designed in a way that fully remote characterization and assessment can be carried out by exploiting web-mapping platforms according to the crowd-sensing paradigm. The workflow, designed consistently with a structural engineering perspective, has been tested with reference to a number of bridges crossing the Tiber river in Rome (Italy), showing that the proposed fully remote monitoring procedure can effectively support satellite data processing and interpretation. Moreover, some issues in view of the general use of satellite data for bridge monitoring emerged from the study. Gaps in the measurement point distribution over the bridge decks are frequently observed over all the monitored area, therefore simplified methodologies aimed at estimating expected displacement ranges of different bridge typologies under serviceability loads have been defined enabling a rational interpretation of the data in the light of the selected radar sensor band of operation. Simplified formulations and charts for service and environmental loads are then presented with a twofold objective: (1) supporting the satellite data elaboration and interpretation by means of easy to manage open-source tools; and (2) providing estimates of the expected operational displacements of healthy structures to guide data interpretation and even algorithms for radar signals processing able to incorporate the response of structures to temperature variations.