Azimuth Reverse Vsp Tomography

The paper proposed the methods of multi-azimuth inverse VSP tomography to calculate near-surface velocity aimed replacing micro-log method at complex surface places. Then, the development of the tomography is reviewed in brief, while the status in quo of this technique is investigated. And analyzing two key facts in using the method, first, yield data gather; second, solve near-surface velocity after tomographic inversion. In the yield data acquire multi-line geometric in a radial pattern is adopted. Before theoretical explanations about the non-uniqueness of inversions and the necessity of constrains are illustrated, the description of Linear Travel-time Interpolation(LTI) calculations, the derivation of Jacobian linear equations, and the deductions of solving large sparse matrix equations, i.e. the LSQR iterations, are involved. In order to cope with the uncertainties in tomography, we reach several categories on constraint methods. Last using model and real data to test the multi-azimuth inverse VSP tomography, and making a conclusion for the method.