On the directivity index of seafloor seismic arrays under isotropic ambient noise excitation

By deriving a model-based spatial correlation function for fluid–solid interface vibrations in isotropic fields, this paper establishes a semi-analytical framework for predicting the array noise response and directivity index of ocean-bottom seismometer arrays, explicitly accounting for vector sediment vibrations and multi-component beamforming. The proposed framework is validated using measured data, showing good agreement between theoretical predictions and experimental observations. Numerical simulations reveal that the spatial correlation structure of the ambient field plays a decisive role in shaping the directivity index, while array aperture and sensor configuration determine how this correlation is mapped onto array performance in isotropic environments.