Picking far-offset arrival times on common-source gathers

Joe Wong

A processing flow that uses a modified energy ratio (MER) attribute is effective for automatically picking first-arrival times near the hyperbolic apexes of common-source gathers. At the flanks of the hyperbolas, where the source-receiver offsets are large and the signal-to noise ratios of the first arrivals are small, a signal-enhancement technique employing three-trace summation along a range of time-space slopes must be used to increase signal-to-noise ratios before MER picking. Even after signal enhancement, many of the MER picked times at far source-receiver offsets will be outliers. However, when source-receiver offsets are large, arrivals on common-source gathers tend to have time moveouts that are almost linear with receiver position. A Radon transform helps to identify slowness and time-intercept values that most closely match the observed linear trends. Outlier MER picked times will have large deviations from the linear trends identified by the Radon transform. These outliers can be eliminated, and the remaining times and their receiver positions can be fitted with least-squares straight lines to provide interpolated times for receivers with missing or rejected MER times.