Microphone and geophone data analysis for noise characterization and seismic signal enhancement
Alejandro David Alcudia León
Source-generated noise, such as air waves and ground roll, is a major challenge in land seismic acquisition. Since much of the surface noise in geophone records arises from a direct impact of air pressure on the geophone case or by conversion of air pressure into ground motion or vice versa, it might be possible to measure air pressure and use it as reference for surface noise attenuation. Microphone data is recorded during land seismic data acquisition to provide air pressure measurements proximal to the geophones. A combination method is developed in the time-frequency domain with the aid of the Gabor transform to suppress the air noise on the geophones. This method is based on the construction of a "mask" function from the microphone Gabor spectrum by setting a threshold on its Gabor coefficients. Then, multiplying the geophone Gabor spectrum with the "mask" function achieves a deterministic cancellation of the associated air-noise component in the geophone. This methodology is applied to two different 3C-2D seismic surveys conducted in Western Canada in 2000 and 2008. In these surveys, the strongest noise measured with microphone prototypes (designed, manufactured and tested by the CREWES Project), is the air blast (or air wave). The results show consistent air wave measurements (both in amplitude and waveform) from trace to trace in the microphone data. The air wave on geophone shot gathers is successfully attenuated by using multiple "mask" functions derived from the microphone data on a trace-by-trace basis. In a separate experiment, a comparison between a single microphone prototype and a calibrated microphone and two professional audio recording microphones, suggests that all microphones under test respond quite similar at frequencies where the source-generated air wave is strongest (>100 Hz). In contrast, all microphones respond very differently to low frequencies, where other noises such as surface waves are dominant (<30 Hz).