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海洋地震勘探中使用气枪阵列,入射到地下介质中的远场地震子波是所有单枪理想子波的叠加。由近场检波器记录的近场子波求取单枪理想子波,进而合成可靠的远场子波,是海上地震勘探子波处理的关键问题。针对这个问题,常用算法在时间域进行子波的分解与合成。由于单枪理想子波传播到检波器的时间不是采样间隔的整数倍,因而时间域方法涉及到地震信号的重采样,不仅计算复杂,而且存在插值误差。本文根据频率域相位与时间域时间延迟的关系,提出了利用傅里叶变换将实测的近场子波变换到频率域,在频率域实现子波谱的分解与合成,再变换回时间域的方法。该方法避开了重采样问题,可以得到精确的单枪理想子波和可靠的远场子波。这种方法还可以考虑虚反射的影响,同时实现子波分解与虚反射消除。模型测试与实际数据试处理表明了本文方法的正确性与可行性。
The use of air gun arrays in marine seismic exploration and the far-field seismic wavelet incident on the subterranean media is the superposition of all single-shot ideal wavelets. The near-field wavelet recorded by the near-field detector seeks a single-shot ideal wavelet, and then the reliable far-field wavelet is synthesized, which is a key issue for the wavelet processing of the marine seismic exploration. In response to this problem, commonly used algorithms are used to decompose and synthesize wavelet in the time domain. Because the single-shot ideal wave propagates to the detector is not an integer multiple of the sampling interval, the time-domain method involves the resampling of the seismic signal, which is not only computationally complicated, but also has interpolation error. According to the relationship between the frequency domain phase and time domain time delay, this paper proposes a method to transform the measured near-field wavelet into frequency domain by using Fourier transform, to decompose and synthesize the spectrum in frequency domain and then transform back to time domain. This method avoids the problem of resampling and can obtain the accurate single-gun ideal wavelet and the reliable far-field wavelet. This method can also consider the impact of the virtual reflection, while achieving wavelet decomposition and deconvolution elimination. The model test and actual data test show the correctness and feasibility of this method.