Comparison of in situ and interferometric synthetic aperture radar monitoring to assess bridge thermal expansion

Asset owners responsible for the management and maintenance of bridges value the collection of data that can be processed into useful information to inform decisions about future management of structures. Installing, powering and receiving data from sensors is not always convenient or possible, but satellite monitoring may provide the ability to measure bridge movements and thus provide an indication of potential problems for asset owners to take action on. This study presents the results of satellite monitoring of the Hammersmith flyover, London, UK, using the interferometric synthetic-aperture radar (InSAR) technique. Sentinel-1 (free) and Cosmo-SkyMed (commercial) satellite radar data were processed to provide millimetre-scale measurements of the flyover and surrounding region and validated with in situ sensor measurements. A method was developed for selecting and comparing InSAR measurements with in situ displacement and temperature measurements, making use of bridge geometrical and structural modelling information. The results compare in situ sensor measurements with remote InSAR measurements and show the suitability of such measurements in measuring thermal expansion for some (but not all) bridge assets. The proposed techniques, illustrated with the case study of the Hammersmith flyover, will enable asset owners to collect regular measurements of bridge movements to complement and add value to current inspection methods and potentially give early warning to defective bridge bearings.