One of the inherent requirements for a successful onshore seismic survey is to ensure that ground motion is measured accurately. Our ability to record ground motion is greatly affected by the inherent response of the geophone and its coupling to the ground. Most practitioners are familiar with the natural (resonant) frequency and damping of geophone elements. Less well known, is that coupling also has a resonant frequency. If a geophone is inadequately coupled then this resonant frequency can appear in the bandwidth of interest. Unlike the natural frequency of a geophone, however, this variation of natural frequency with coupling can result in the output of the geophones varying across the survey area if the coupling varies. Complicating the identification of coupling effects is the influence of ambient noise. Wind noise, for example, predominantly occurs from the wind moving surrounding vegetation which creates noise that is transmitted through the ground. As better coupling improves the ability of the geophone to record ground motion, then it necessarily also results in an apparent increase in transmitted wind noise. Better coupling, however, also improves the strength of the signal component and thus the SNR of the data improves. Improving the coupling of geophones often involves burying them, which obviously requires additional time and therefore expense. The question, therefore, is if the additional expense taken to improve geophone coupling is worthwhile, and are there alternative approaches to reducing ambient noise? As part of a recent survey we conducted an experiment using a variety of differently coupled geophones. The results, from both shot records and stacks, show that data quality is significantly enhanced from burying the nodes, either partially or completely, rather than placing them on the surface.

Open-Access Online Publication: May 29, 2023