Deghosting by echo-deblending

Abstract

Because of the strong sea surface reflectivity, a marine source generates both a direct wavefield and a ghost wavefield. This corresponds to a blended source array, the blending process being natural. Consequently, deghosting becomes deblending ('echo-deblending'). We discuss source deghosting by an iterative deblending algorithm that properly includes the angle-dependence of the ghost: it represents a full-wavefield solution. The method is independent of the complexity of the subsurface: only what happens at and near the surface is relevant. This means that the actual sea state causes the reflection coefficient to become frequency dependent and the water velocity may not be constant due to temporal and spatial variations in the pressure, temperature and salinity. As a consequence, we propose that estimation of the actual ghost model should be part of the echo-deblending algorithm. This is particularly true for source deghosting, where interaction of the source wavefield with the surface may be far from linear. The proposed echo-deblending algorithm is also applied to the detector deghosting problem. The detector cable may be slanted and shot records may be generated by blended source arrays, the blending being man-made. Finally, we demonstrate that the proposed echo-deblending algorithm is robust for background noise.