Source-side Up-down Wavefield Separation Using Dual NFHs

We propose a method of source-side separation of up- and down-going acoustic wavefields in order to predict accurate far-field signatures of airgun arrays from reflection-free near-field data. The separated down going component of the wavefield can be then used for estimation of the effective sea reflection coefficient, which can depend on frequency and the angle of incidence at the sea surface.

The technology is based on simultaneous measurement of near-field pressure P and z-component of the gradient of pressure dP/dz of the wavefield produced by airgun array marine seismic source. By combining P data with dP/dz data it is possible to remove the down going component of the wavefield that is due to reflections from the sea surface. In order to measure P and dP/dz, a pair of vertically distributed NFHs can be used.

Numerical examples provided in the paper illustrate that the present method outperforms the conventional method of Ziolkowski on estimation of airgun notionals from NFH measurements in cases when assumed sea surface reflection coefficient is wrong. Field test of the proposed algorithm is in progress.