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Figure 1: Photos of the Adolphe Bridge and instruments used and information on the measurement setup. (a) Sideview of the Adolphe bridge (source: Wikimedia Commons). (b) View from below. (c) Measurement setup used on the Adolphe bridge. (d) Wireless sensing unit (WSU) used for the ambient vibration measurements on the Adolphe bridge. The central part of the unit, including the digitizing board, is contained in the box shown in the center of the picture, with antennas for wireless data transmission. The 4.5 Hz geophone is the yellow instrument shown on the right. On the left, the battery providing the necessary power supply is depicted. (e) Deployment of one WSU on the bridge walkways. The geophone (yellow) is centered in a horizontal position on the walkway, with the two horizontal components oriented in the longitudinal and transverse direction with respect to the bridge, respectively. The red object in the picture is a Tromino® sensor deployed by the Geological Survey of Luxembourg for comparative purposes.