1. n. [Formation Evaluation]

A technique used for identifying and measuring the slowness and time of arrival of coherent acoustic energy propagating across an array of receivers. The different packets of coherent energy can then be identified in terms of their origin, for example compressional, shear, Stoneley or other arrivals. In formation evaluation slowness-time coherence is used in conjunction with an array-sonic tool in which the full waveforms at each receiver have been recorded. The technique consists in passing a narrow window across the waveforms and measuring the coherence within the window for a wide range of slownesses and times of arrival.

See: full waveform,  sonic log,  sonic measurement,  Stoneley wave