Locating Lightning Using Electromagnetic Time Reversal: Application of the Minimum Entropy Criterion

We present a new method based on Electromagnetic Time Reversal (EMTR) to locate lightning return strokes. The application of classical EMTR criteria such as the maximum field peak or the maximum energy to locate radiation sources would not work if the medium is inhomogeneous and/or has scatterers. The proposed method makes use of the fact that the spatial distribution of the field is characterized by a minimum entropy at the time at which the time-reversed back-injected waves reach the source. The focusing time is first determined by evaluating the entropy of the field as a function of time. The last local minimum of the entropy corresponds to the focusing time. The location of the source is determined by examining the spatial distribution of the electric field at the focusing time: the maximum value corresponds to the source location. The application of the proposed method is illustrated considering a 2D example including 4 scatterers and 4 sensors. The forward and reversed time simulations are performed using a 2D-FDTD model with PML boundary conditions.