Evaluation of a Broadband Marine Source

Abstract

A standard seismic source is comprised of an array of air-guns all placed at the same depth, so that all guns contribute to a single ghost response. The interference between primary and ghost can reduce bandwidth. Broadband air-gun arrays are designed to attenuate the source ghost by placing guns at a range of depths within the array which diversifies the frequencies at which the source ghost notch appears for each gun. This leads to a flatter spectrum and an expectation of improved bandwidth with respect to a standard source. We evaluate far-field signatures and compare processing results for a 2D test-line acquired with an experimental broadband source and a standard source. Parkes and Hegna, (2011) and Siliqi et al. (2012) have also recently studied the broadband array concept. Our investigation differs in the details of the processing and of the analysis of results. The standard source data we use as reference were processed up to the Nyquist frequency and not just up to the first source ghost notch frequency. This allows an objective assessment of the processing and broadband array solutions to the source ghost problem. The datasets were processed using essentially identical prestack time migration sequences, which included source- and receiver-side de-ghosting, and the data were then evaluated in terms of signal coherency.