The source scaling law: Air-gun signature estimation using field data

Abstract

Recent advances in marine broadband seismic data acquisition have led to a range of new air-gun source configurations. The air-gun arrays have conventionally been kept at a constant depth, but in order to attenuate the source ghost reflection new multi-level sources have entered the marked. The bubble-time period for a bubble generated by an air gun is dependent on, amongst many parameters, the firing depth. We use quasi-near-field measurements of air gun signatures to validate the well known source scaling law. Air-gun signatures was measured from a 600-in3 air gun fired at different depths with the same initial pressure of 2000 psi. We find that the source scaling law can be used to estimate a source signature from one depth knowing the source signature from a different depth from the same gun. The error between the estimated and measured source signatures is dependent on the difference in source depth. For a depth difference of ±5 m we estimate signatures that have NRMS-difference ranging between 4 6 % from the measured signature at the given depth, and 7-12 % when the difference is ±10 m. The NRMS-difference increase as the difference in source depth increase and better results are obtained when large firing depths are used. Our results are not clear enough to validate the source scaling law, but they show that it works very good for relatively small depth variations.