First break picking

[1] First-break picks associated with the refracted arrival times are used in an inversion scheme to study the near-surface low-velocity zone and subsequent determination of static corrections.

Gelchinsky and Shtivelman[2](1983) used correlation properties of signals and applied a statistical criterion for the estimation of first arrivals time.

Fabio Boschetti et al.[5](1996) introduce a fractal-based algorithm, which detects the presence of a signal by analyzing the variation in fractal dimension along the trace.

A direct correlation method was introduced by Joseph et al.[6](1999) which was developed for use in highly time-resolved, low-noise signals acquired in the laboratory.

In this method, the greatest value of Pearson's correlation coefficient between segments of observed waveforms near the pulse onset and at an appropriate reference serves as the time determination criterion.

When the instantaneous absolute amplitude exceeds an automatically adjusted threshold, ratios based on the averages of the windows over previous time samples provide standards to differentiate signals from unwanted noise.

2.Thresholds is defined as where Em is mean and Esd is standard deviation; p is the number of shifted samples; α is the coefficient to adjust the height of the first threshold and is taken to be 3.

For an impulsive first arrival, the height of the absolute amplitude and the representative gradient at the trigger point can be used to accomplish the correction.