The airwave in hammer reflection seismic data

The seismic wave propagating due to air-coupling between source and geophones is commonly called the \"airwave\". Serious problems to the seismic data processing can arise from the presence of airwave arrivals in the data. The low apparent velocity of the airwave, in conjunction with the high frequency content of its pulse, suggests using a very dense geophone geometry in order to be able to record with adequate spatial sampling. When an inadequate spatial sampling is used, F-K filtering has problems in its proper implementation and usually various techniques must be applied to overcome them. In the shallow seismic reflection method, pre-emphasis filtering can lead to spatial aliasing of the airwave over all its frequency bandwidth. In order to maximise the ratio of signal to \"removable\" noise, analog filters should not be set greater than a limit defined by the receiver interval. Altematively to elimination of the airwave in the processing stage, the effectiveness of airwave suppression at the generation stage (at the source) is tested, as well as cancellation of reception of the airwave by the geophones. The use of a plastic plate in the \"hammer and plate\" source instead of a metallic one can limit production of airwave. In common offset sections, the airwave arrivals form a straight horizon parallel to the distance axis. This can be useful as a tool for finding any changes in offset due to an incorrect synchronisation between source and receivers. In the present paper an example of the dependence of the airwave on variations in temperature is also given.