Low frequencies are very important in seismic imaging. They penetrate deeper and they are indispensable in impedance estimation. High frequencies enhance the resolution and provide detailed information. In this paper the following three steps are proposed to realize ultra wideband seismic images: a) broaden the linear bandwidth during acquisition by applying DSAs (dispersed source arrays), b) add the missing ultra-low frequency information (trend) from migration velocities, indispensable for impedance images, and c) add the missing ultra-high frequency information (detail) by data obtained from borehole measurements, particularly for reflectivity images. @en

A marine source generates both a direct wavefield and a ghost wavefield. This is caused by the strong surface reflectivity, resulting in a blended source array, the blending process being natural. The two unblended response wavefields correspond to the real source at the actual location below the water level and to the ghost source at the mirrored location above the water level. As a consequence, deghosting becomes deblending ('echo-deblending') and can be carried out with a deblending algorithm. In this paper we present source deghosting by an iterative deblending algorithm that properly includes the angle dependence of the ghost: It represents a closed-loop, non-causal solution. 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 created by simultaneous sources. Similar to surface-related multiple elimination 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 may cause the reflection coefficient to become frequency dependent, and the water velocity may not be constant due to temporal and lateral 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 echo-deblending theory also shows how multi-level source acquisition and multi-level streamer acquisition can be numerically simulated from standard acquisition data. The simulated multi-level measurements increase the performance of the echo-deblending process. The output of the echo-deblending algorithm on the source side consists of two ghost-free records: one generated by the real source at the actual location below the water level and one generated by the ghost source at the mirrored location above the water level. If we apply our algorithm at the detector side as well, we end up with four ghost-free shot records. All these records are input to migration. Finally, we demonstrate that the proposed echo-deblending algorithm is robust for background noise.@en

The migration of full wavefields (primaries + multiples) by using the concept of secondary sources at each subsurface grid point is summarized. These secondary sources are two way and contain the grid-point reflection as well as the grid-point transmission properties. They "assist" the primary sources in illumination of the subsurface. Full-wavefield migration is implemented as a closed-loop process in which the estimated reflectivity properties are used to generate all higher-order scattering (multiples and transmission effects), such that the modeled full-wavefield response matches the observed measurements. In addition, velocities can be updated simultaneously. Theoretical considerations and examples lead to the principal conclusion that multiples should be used, not removed.@en

The future in seismic exploration and seismic monitoring is the inclusion of all orders of scattering in the imaging and inversionalgorithms. Using the full wavefield in an inversion process allows us to surpass imprints provided by incomplete acquisition and provide more accurate information on the subsurface, as noise becomes signal. We describe an inversion process that does not use the standard parameters from finite-difference-type modeling (being local velocity and density) but that describes the seismic
data in terms of elastic reflectivity operators and propagation operators. With these operators, our full-wavefield modeling process builds the complete two-way seismic response. A major advantage of our alternative to the traditional full-waveform inversion methodology is that reflectivity operators are traveltime-free and
propagation operators are scattering-free, making the inversion problem significantly more linear. A major advantage of our algorithm is (1) that multiples are utilized to improve both image and velocity accuracy, and (2) that both image and velocities are utilized to make a contribution in the nonlinear migration process. Hence, in joint migration inversion, multiples have a twofold active role.@en

Low frequencies are most important in seismic imaging. They enhance the resolution, penetrate deeper and they are indispensable in impedance estimation. In this paper a fourstep approach for enhancing the low frequencies in marine acquisition and (pre)processing is proposed: 1) positioning the sources and detectors at the optimum depth, 2) carrying out proper deghosting and 3) (pre)processing the low frequencies separately. In step 4), the missing ultra-low frequency information (trend) comes from the velocity distribution and from modern gravity gradiometry. @en

It is shown that deghosting is actually a data-adaptive deblending process. This special deblending process is nonlinear and can be carried out such that the effect of noise is minimized. Our algorithm is explained and illustrated with examples. @en