About Semblance Filtering in (Tau-P)-Domain
Semblance or slowness time coherence (STC) is the main tool for estimating the interval times (velocities) of the wave packet components when using multielement acoustic logging. The idea of semblance in the (τ-p)-domain is that visualization of matrices of its values assumes spots of bursts of coherent energy of a finite number of constituent waves (P, S, St, casing, and collar) located in the vicinity of the tool line. The semblance analysis can be complicated for several reasons. The first is the need to select the value of the mandatory time window (half-window) of averaging, which, in fact, coarsens the distribution of coherent energy. The identification and localization of the spots of the semblance image can be hampered by interference and quantization noise (time step and distance between receivers). Also, in standard processing, it is not always possible to perform a clear tracing of the interval timelines for the components of the waves in depth. Here, we present two new semblance matrices filtering methods that partially address some of the disadvantages of traditional semblance.