Sensitivity kernels for finite-frequency ocean acoustic observables

Abstract

Wave theoretic modeling was applied to obtain sensitivity kernels representing the amount by which ocean acoustic observables, such as pressure, intensity, or arrival times, are affected by localized sound-speed variations anywhere in the medium. These kernels can be derived using the first Born approximation, yielding an integral representation of observable perturbations as functionals of sound-speed perturbations. The kernel in each integral represents the spatial sensitivity of the observable to sound-speed perturbations in the medium. The travel-time sensitivity kernel represents a full-wave generalization of the highly localized ray kernel from geometric optics. This work extended recent wave-theoretic results for the travel-time sensitivity kernel for short-range propagation in simple environments to long-range transmissions in more complicated ocean environments relevant to ongoing propagation and inversion experiments. It was shown that the geometry of the wave-theoretic sensitivity kernels is related to the geometry of Fresnel volumes surrounding eigenrays, provided that the effects of refraction are taken into account for the calculation of the latter. [Work supported by ONR.]