瞬时频谱分析法在海洋电磁信号分析中的应用

The Instantaneous Spectrum Analysis Method in Marine Electromagnetic Signals

海洋可控源电磁法(CSEM)是近年兴起的一种探测海底油气的地球物理技术。CSEM在深海取得了很好的效果,但是在浅海受空气波的影响严重,沿空气-海水分界面传播的空气波会完全掩盖从高阻储油层返回的有用信号。通过对时频分析技术的研究,达到对空气波的压制的目的。研究和对比短时傅里叶变换、WignerVille分布和希尔伯特-黄变换3种常用的时频分析方法,选取Wigner-Ville变换对海洋电磁信号进行时频分析,因为海洋电磁信号在空气和海底中传播速度的不同,所以接收点通过两种途径接收到的信号的时间也不同,通过理论计算进而判断出所需要的海底传播的信号,为压制空气波提供技术方法。

The seabed abounds in oil and gas resources,marine controlled source electromagnetic（ CSEM） is a new geophysical technique of an undersea oil and gas exploration. It has achieved good results in the deep sea. But CSEM in shallow water is influenced since it is disturbed serious by airwave. Along with the air-water interface,the air wave will completely conceal useful signal propagated from high reservoir return. By researching and comparing three commonly used time-frequency methods i. e.,short-time Fourier transformation,Wigner-Ville distribution tranformation and Hilbert-Huang transformation, the paper then selects the Wigner-Vill transformation to analyze the marine electromagnetic signals. The propagation velocities of the CSEM signal in air and underwater are different,therefore,the reception times of the received signal of the two types are different. By theoretical calculation,it can identify the useful signal. It provides amethod to suppress air wave.