9 Exploiting Imaging Techniques to Overcome the Limits of Vibration Testing in High Excitation Level Conditions 99 Fig. 9.9 FRF sum for the four different data set: SLDV, image data sampled with 61 points on the upper section and image data sampled with 61 points, average of the upper and lower profile Fig. 9.10 Mode shapes for the four different data set: SLDV, image data sampled with 61 points on the upper section and image data sampled with 61 points, average of the upper and lower profile 9.5 Conclusion This paper aimed at discussing the suitability of image-based measurement techniques for providing valid data for Operational Modal Analysis. This is an important aspect to be analysed, since LDV-based methods fail when extremely high excitation levels, and therefore also high displacements, are reached. The study has been conducted on a simplified test rig by comparing the outputs of standard LDV-based EMA and the outputs of OMA, when OMA is performed on data extracted from a high speed camera. Despite this work aims at proposing the image-based approach as a valid alternative in high excitation levels tests, measurements presented referred to excitation levels where LDV could still be considered
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