Automatic first arrival picking using energy ratios

Abstract

First arrival auto-picking has become very important, especially with the increase of acquired field data. Coppens (1985) proposed to use the energy ratios over receiver or offset gathers, rather than trace amplitude in the shot gather, in order to pick the first arrival times. Seismic data must be subjected to preconditioning processing to minimize noise and to stabilize the first arrival for picking. Narrow band-pass filtering and amplitude balancing are needed to precondition the seismic data. In this thesis, I establish a new method for estimating the first-arrival time. This method outputs three values from the energy-ratio curve: Max., Min., and threshold percentage from the Max. toward the Min. The threshold percentage depends on the noise prior to the first-arrival because the slope of the energy-ratio curve is affected by the noise. The result of manual picking shows problems in the stack caused by picking the wrong refractors. In noisy areas, manual picking could easily mislead the processor because of mixing the first arrival with other arrivals. The auto-picking method shows encouraging results over the tested area. The three steps for auto-picking of the first-arrival are the following: converting the amplitude to energy ratios, auto-editing, and posting the picks into the shot gathers for quality control. A Voxel-geo package was used to manually pick the first-arrival. Another software package called the GLI static refraction package was also used.