Abstract:

First-arrival times at high transmitter-receive angles are often very difficult and inaccurate to pick up by   conventional methods  because of low signal/noise in the data.  We introduce a new traveltime picking scheme based on cross-correlation. First, we normalize each trace by signal maximum and  sort the data into common-ray-angle gathers. Then, we align traces in each common-ray-angle gather by cross correlating with the other trace of  the highest signal-to-noise ratio, determine mean trace for each angle gather. Finally, we pick first-arrival time on each mean trace, cross-correlate each trace in data set with appropriate reference waveform for that angle, and determine first-arrival time. In the test of synthetic data and field data, the approach improves the results. Compared  with velocity tomography derived from common time picking technology, the new velocity tomography is more accurate, more clearly, and more helpful to distinguish the target under the ground.

Key words: borehole radar, first-arrival time, high transmitter-receive angles, tomography, cross-correlation