Fiber lasers are becoming new effective sources for coherent lidars, thanks to their spatial and spectral qualities. Allowing operation in continuous, modulated and pulsed modes, their increasing power at eyesafe wavelengths is well suited to anemometry, velocimetry, vibrometry or laser imagery. Requested laser qualities are discussed, concerning wavelength, power, pulse duration and frequency, beam shape and spectral width, and compared to existing fiber source parameters.

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Coherent Lidars are able to finely measure the vibration velocity of remote targets. This allows Operative Modal Analysis (OMA) of potentially damaged buildings, for their diagnosis at a safe distance after a seismic event. As a next step from our previous work validating this method for modal frequency determination, we have assessed its capability to extract the full modal parameters of RC buildings, including mode shapes, using multiple ambient vibrations measurements by Lidar on the entire structure. We report on the development and field trial of a 3-path Lidar vibrometer for this purpose. After a description of the system, we show that application-related constraints are fulfilled: low velocity noise, real-time signal processing, compact and laser safety. Then, we present the results of a real-scale trial on 3 buildings in Grenoble, France. We discuss the reliability of this technique for remote structural diagnosis with a comparison of modal parameters, as measured by Lidar at 200m range and in situ velocimeters.

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