Research on OBN secondary location method in shallow water environment

Accurate observation system information is the foundation of high-precision seismic data processing. Due to the inability to use conventional GPS positioning for OBN receiver points, specialized technical means are usually required to determine the coordinates of the receiver points. Common secondary positioning methods for receiver points include least squares method, approximate tetrahedron method, search method, fitting surface method, equivalent velocity method, vector synthesis method, etc. However, they are all based on direct wave travel time for positioning. Shallow water OBN data only has direct waves within a small offset distance, making those methods difficult to apply. Another commonly used secondary positioning method is refracted wave secondary positioning, which has low positioning accuracy due to its inability to handle speed gradients, interface bending, and other situations. In response to the problem of inaccurate positioning of receiver points in shallow water environments, this paper proposes a positioning method based on first arrival travel time fitting. Firstly, the first arrival time is accurately picked up from the common receiver point gather. Then, a polynomial is used to fit the relationship curve between the first arrival time and offset. The coordinates of the receiver points are adjusted by the difference between the actual picked travel time and the corresponding value on the curve, and multiple iterations are carried out until convergence. Finally, based on the water depth values measured in the survey, the corresponding Z coordinates can be obtained by projecting the X and Y coordinates of the receiver points, thus obtaining accurate three-dimensional coordinates of the receiver points. The method proposed in this article has been applied to both simulated and actual OBN data, achieving ideal results.