Diffusion Coefficient Estimation and Its Application in Interior Change Evaluation of Full-Size Reinforced Concrete Structures

Parameter-based imaging from passive multispectral polarimetric measurements

“…4 show the estimated mean and standard deviation (error bars) of n, k, ρ d and σ 2 as a function of wavelengths for the selected areas in the two scenes. The estimated n of the concrete and gravel are close to 1.5, which is reasonable because their main composition is presumably silicon dioxide [35]. The refractive index values for the container and car hood are in the 1.40 to 1.45 range and indicate a small imaginary part (k).…”

Condition Evaluation of an Existing T-Beam Bridge Based on Neutral Axis Variation Monitored with Ultrasonic Coda Waves in a Network of Sensors

“…These features are well-known to severely affect the performance of traditional direct wave-based techniques. Fortunately, previous studies in the fields of optics, acoustic, and geophysics demonstrate that noise-like coda waves contain detailed information about internal structures, and they are very sensitive to changes occurring in the large volume of a medium [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. This sensitivity is attributed to the fact that coda waves propagate following complex trajectories not limited to the direct path between two sensors, and they may traverse the regions of interest repeatedly.…”

“…Thanks to these properties, coda waves have been successfully used for several NDT&E applications, mostly on laboratory scales. Depending on practical applications, these coda wave-based techniques can generally be separated into two categories: evaluation of global structural health [ 16 , 17 , 18 , 19 , 20 ] and characterization of cracks [ 21 , 22 , 23 , 24 , 25 , 26 ]. The first category focuses on global structure monitoring through the use of coda wave interferometry (CWI) [ 27 ] or diffusion equation [ 11 ] to quantify coda signal changes.…”

“…The first category focuses on global structure monitoring through the use of coda wave interferometry (CWI) [ 27 ] or diffusion equation [ 11 ] to quantify coda signal changes. Then, with the help of a sensor network and further analysis, such as Mahalanobis distance [ 18 ] and diffusivity [ 20 ], the location, type, and magnitude of changes can be estimated up to a certain extent. The other category aims at identifying the locations, depths, and numbers of cracks with a high degree of accuracy.…”

“…An inversion procedure is then adopted to calculate the density of changes at each localized position through inverse algorithms, such as maximum likelihood [ 23 ], sensitivity kernel [ 24 , 25 , 26 ], and interpolation [ 21 ]. For additional details on the techniques, we refer the reader to the literature reviews published in References [ 20 , 25 ].…”