Borehole tools are provided with at least one transmitter which generates acoustic waves at a plurality of azimuthal locations about the borehole, and at least one receiver which receives and measures a characteristic (e.g., velocity) of the acoustic waves at related azimuthal locations. The direction...http://www.google.de/patents/US5544127?utm_source=gb-gplus-sharePatent US5544127 - Borehole apparatus and methods for measuring formation velocities as a function of azimuth, and interpretation thereof
