Calibration of source level, expected transmitted power, and reverberation for long‐range sonar in fluctuating range‐dependent ocean waveguides

Abstract

The ocean waveguide is temporally and spatially varying. An acoustic signal transmitted through the ocean or scattered from objects will get randomized. Estimating parameters of sonar, the environment, and scatterers requires a statistical approach that incorporates medium uncertainties into the signal analysis. Here we discuss source level, transmission loss (TL), and reverberation model calibration using data acquired with a long‐range sonar on the New Jersey STRATAFORM. Broadband acoustic data measured by a desensitized hydrophone in a towed horizontal receiving array at numerous locations from a vertical source array are analyzed. The match‐filtered data are compared to the expected TL output from a parabolic equation model that accounts for bathymetric variations. A maximum likelihood estimator is implemented to provide a global inversion of the data for source level, attenuation due to scattering, and match‐filter degradation in the multi‐modal ocean waveguide. An estimate is also provided of the coherence bandwidth for broadband acoustic signal transmission in this environment. A challenge in calibrating bottom reverberation models with sonar data lies in separating the scattered intensity from moving objects, such as fish groups, and distinguishing them from the statistically stationary background reverberation. An approach is presented for this purpose.