Microphone suppression of air-noise on geophones
Air-noise in seismic records creates a loss in signal quality, reducing seismic image clarity. A microphone may be used to estimate and remove air-noise in seismic records. This thesis covers the characterization of air-noise on a prototype 4-Component geophone (3-C geophone plus microphone), as well as the development of two air-noise removal filters. Vibration-isolated, noise characterization experiments were performed to determine the 4-C geophone’s directional and frequency dependent response to air-noise. Sensor placement within the geophone appeared to affect each geophone component’s directional response; showing increased sensitivity to sounds from the same side the sensor was mounted. In addition, a walk-away seismic survey was performed to determine the effect of distance on geophone air-noise. Peak amplitude decay rates differed from the theoretical 1/R, R representing total distance. The microphone and inline geophone decayed at 1/R^1.4, the crossline component at 1/R^1.15, and the vertical component at 1/R^1.81. These results indicate a loss of energy to heat through air-ground interactions. Results from the noise characterization tests were used to develop two air-noise filters; a real-time filter, which could remove air-noise from geophone signals before they are recorded; and a post-acquisition filter, which could be used to more precisely remove air-noise. Both filters were effective at reducing air-noise, up to 21 dB reduction for near offsets. However, the real-time filter affected seismic data due to microphone recorded seismic events.