Estimation of focusing operators using the Common Focal Point method

Abstract

The objective of this PhD project is to present a data-driven method to determine one-way focusing operators. Focusing operators are the input for imaging a subsurface structure from measurements at the surface. They can be used in imaging the earth's interior, and also in non-destructive imaging of e.g. wings of aeroplanes or in medical imaging for detection of uterus cancer. This thesis focuses on methods for the exploration seismology. Focusing operators are one-way propagation operators for acoustic wavefields describing the propagation from one subsurface point, the focal point, to the surface locations. They are often parameterised as traveltime operators and amplitude (weight) operators. The traveltime and the amplitude operators are estimated in a data-driven manner. No a priori information such as a velocity model is used. Using the Common Focal Point method a data-driven estimation strategy is found with implementations for different geologies. Mainly, the traveltime operator can be estimated by an iterative method based on the Principle of Equal Traveltime and the Data Matching Principle. Once the traveltime operator is found, the confocal reflection amplitudes for one single focal point for each source-receiver pair can be extracted from the shot records. These are displayed in a CFP matrix. The amplitude function can be represented as an eigenvector of the CFP matrix. The obtained operators are non-smooth containing all measured propagation effects, and therefore are capable of producing improved images and provide optimal input to tomographic methods.Applied Science