Patent ID: 6704657
Filing Date: 2004-03-09
Classification: G01V

Abstract:
A method for measuring the first arrival time TR of seismic first arrival waves in the seismic exploration, wherein the method comprises:using a or several detectors to measure seismic waves and convert said seismic wave signals into electrical signals; using a signal processing means connected with the output of said detector to carry out a real time processing of signals outputted from the detector in order to determine the accurate first arrival time of seismic first arrival waves, wherein the signal processing means performs at least the following steps: a) getting samples of signals outputted from the detector and converting them into signals, and specifying an initial recorded signal Wi(t); b) using a first time window of size twin1 to carry out an avenge energy calculation and record the outcome as Ea(t); c) setting a threshold value e for Ea(t), specifying the time when Ea(t) changes from less than e to greater than e as ts, and determining preliminarily that the first arrival wave has arrived; d) after time ts, obtaining the time of appearance of the first maximum value of Ea(t), and specifying it as tf, which can indicate the approximate location of the Â¼ cycle of the first wave of first arrival waves; e) using a second time window of size twin2, starting from time ts, carrying out a mean energy calculation and recording it as Ej(t), wherein twin2>twin1, with the purpose to check out whether the conclusion of step c) on the arrival of the first arrival wave is correct; if ej(t)>e within time cycle twin2 following tf and keeps increasing, then the actual arrival of the first arrival waves is determined; otherwise, then after finding time t1 when Ea(t1)1; f) upon Wi(t), approximately determining the jump time Tj of the first arrival wave, then using the spectrum of the first arrival wave to determine preliminarily whether this check is valid; if the difference between the jump time Tj of the first arrival wave and the time tf is less than a threshold time TW, then it indicates that this check is valid; otherwise, it indicates that the check is invalid due to interference, so the procedure can be terminated; g) smoothing Wi(t) by using a smooth filtering method; then searching Wi(t) backward from time tf to obtain a series of zero crossing points as sample values of first arrival time; then calculating the expectation time ta of said sample values in the neighborhood of ts (before ts when the window is of small size, or after ts when the window is of large size) by statistic means; h) using as a specified range for removing the exceptional data outside the range; calculating the expectation time ta; and replacing old ta with new ta and reducing td; repeating step h) until the number of said samples inside the range i) selecting n samples of the first arrival times t(n)(n1, 2, 3 . . . n) in the neighborhood of time ta; observing the sample values of Wi(t) by means of a third time window ;selecting the sample values t(n) of first arrival time TR at which the sum of the values of Wi(t) within time window is smaller than a threshold &egr;; determining first arrival time TR more accurately; and then one of these values with the polarity direction from the first arrival wave being most adjacent to zero is taken as the first arrival time and recorded as TR0, and the procedure is terminated.