Development and Evaluation of a Seismic Monitoring System for Building Interiors—Part I: Experiment Design and Results

Optical motion tracking in earthquake-simulation shake table testing: Preliminary results

“…We use the term AM-FM demodulation to imply the computation of the instantaneous amplitude (IA) functions a n (ξ), instantaneous phase (IP) functions ϕ n (ξ), and the instantaneous frequency (IF) vector functions ω n (ξ) = ∇ϕ n (ξ) = ∂ ∂ξ1 ϕ n (ξ), ∂ ∂ξ2 ϕ n (ξ) = ω (1) n (ξ), ω (2) n (ξ) . For the scope of this paper, the IA, IP and IF computations are carried out via the robust AM-FM demodulation algorithm proposed in [14] (see also [9] and [15] for further details).…”

“…Figure 2(b)) with the AM-FM markers place onto a structure, we proceed to compute the DCA AM-FM demodulation parameters following (2); in particular, we are interested in the dominant instantaneous frequency (IF) vector function with vertical and horizontal components given by ω (1) (ξ) and ω (2) (ξ) respectively. In Figures 2(c) and 2(d) we display the 2-D datasets ω (1) (ξ) and ω (2) (ξ) as images. Clearly, the high contrast areas of the image shown in Figure 2(c) are related to the 2-D sinusoid pattern in the vertical direction (see Figure 2…”

“…Using the highest frequency mode assumption we may follow two approaches to first segment each marker as an entity containing the black circles: (i) compute the histogram of ω (1) (ξ) (or ω (2) (ξ) when appropriate), identify the lower and upper thresholds related to the highest frequency mode (for instance, via [7]) and use such thresholds for segmentation or (ii) manually segment the location of each marker for a given "training" frame, compute the histogram of ω (1) (ξ) (or ω (2) (ξ) when appropriate) in the manually segmented regions of interest (ROI), identify the lower and upper thresholds (again via [7]) and use such thresholds to segment all other frames. The first approach is fully automatic but, even though unlikely in a real scenario, the highest frequency mode assumption may not be true.…”

“…Imagebased systems are reported in [1], [2], [3]; the main drawback of such systems is that they need robust feature detection techniques. For marker-based systems, active and retro-reflective markers are quite popular [4], [5], [6] because the segmentation procedure for such markers is relatively straightforward (based on intensity).…”

“…In 2(c) and 2(d) we display the 2-D datasets ω (1) (ξ) and ω(2) (ξ) as images. ω (1) (ξ) and ω(2) (ξ) are the dominant Instantaneous frequency (IF) of 2(b) in the vertical and horizontal direction respectively (see(2)). Note the high contrast of 2(c), where the vertical AM-FM markers are placed.…”