3D sensing AE sensor Fizeau fiber interferometer GNSS mobile measurements Nakagami parameter OLTC ROC curve Rogowski coil Technology: general issues VAG acoustic emission attenuation boundary conditions circuit modeling coefficient of thermal expansion compounding Nakagami imaging contrast-enhanced ultrasound current measurement defect identification eddy current elastic waves electrodynamic accelerators feature extraction frequency analysis genetic algorithm geometric layout of railway track high-current pulses high-current shunts image processing incubation