Imaging by seismic inversion based on the adjoint state method

Least-squares migration (LSM) has the ability to compensate for limitations in the imaging system and estimate an image that is closer to the earth reflectivity. These favourable properties over conventional imaging have made it the method of choice in complex geological settings. In this paper, we discuss the different properties of LSM and Full Waveform Inversion (FWI) and suggest a new nonlinear least-squares reverse time migration (LS-RTM) implemented in the framework of FWI. The new inversion solution iteratively estimates the earth reflectivity while simultaneously updating the velocity model. We demonstrate the effectiveness of the method through a case study from the Norwegian Sea.