Add to ORKGThe paper describes the application of conventional accelerometers and innovative microwave remote sensing to operational modal testing of a historical slender structure: the bell tower of the Cathedral of Trani. In more details, the natural frequencies and mode shapes of the investigated tower are identified by applying different output-only techniques to the data obtained by means of the two measurement systems. Full details on the experimental procedures, instrumentation and data analysis are reported in the paper; furthermore, accuracy and limits of the radar-based technology in monitoring a stiff historic building are addressed as well
