Mathematical modelling of seismic noise-model description and documentation

Abstract

The objective of this project is to use a mathematical model for the propagation of seismic airgun signals in the water column and to forecast the effect such signals and noise may have on fish and animals in the sea. The model used is the PlaneRay model, a model based on ray theory that can deal with range-dependent bathymetry and depth-dependent sound speed variations. The seismo-acoustic properties of a layered seabed with absorption and shear wave conversion are included in an approximated manner. The model can simulate the total sound field, both in the time and in the frequency domain, out to very large distances. In cases where the ray modelling may be suspect because of its inherent limitations other codes based on different mathematical approaches may supplement the ray model. In this report the wave number integration model called OASES model is used for quality control and benchmarking. The report contains several examples of modelling of synthetic, but relevant scenarios. The result of PlaneRay and OASES are compared and discussed with the objective to understand the limitations of validity potential errors of the codes. A short users guide to the PlaneRay code is included in the appendix.

Oppdragsgiver: Norwegian Petroleum Directorate (NPD)