LOW-FREQUENCY ACOUSTIC VECTOR FIELD STABILITY IN THE PRESENCE OF ENVIRONMENTAL VARIABILITY

Abstract

The Department of Physics at the Naval Postgraduate School recently collected data from a low-frequency vector sensor system off the coast of Big Sur, California, in May 2018. During the test, signals from numerous surface craft were recorded. In this study, a numerical model was employed to estimate the vector field transmission loss at low frequency in order to estimate performance of the system during the test. In order to provide realistic ranges of values, the impact of environmental variability was examined and the primary factors affecting transmission loss were identified. The range-dependent environmental features included varying bathymetry as well as a rough pressure release surface that can predict the effects of rough surface scattering. During the field test, sound speed profile measurements were made, and surface wave buoy data was collected that provided realistic estimates of these features in the vicinity of the sensor system. Various geoacoustic bottom parameters were modeled in order to estimate the potential variability in transmission loss levels due to uncertainty in bottom type. Finally, models of merchant ship source levels were combined with the range of transmission loss predictions to develop estimates for received levels on the vector sensor system during the test. These estimates will then provide a guide during the post-processing of the data collected and may lead to improvements in source level modeling.