Propagation in a waveguide with range-dependent seabed properties

Abstract

The ocean environment contains features affecting acoustic propagation that vary on a wide range of time and space scales. A significant body of work over recent decades has aimed at understanding the effects of water column spatial and temporal variability on acoustic propagation. Much less is understood about the impact of spatial variability of seabed properties on propagation, which is the focus of this study. Here, a simple, intuitive expression for propagation with range-dependent boundary properties and uniform water depth is derived. It is shown that incoherent range-dependent propagation depends upon the geometric mean of the seabed plane-wave reflection coefficient and the arithmetic mean of the cycle distance. Thus, only the spatial probability distributions (pdfs) of the sediment properties are required. Also, it is shown that the propagation over a range-dependent seabed tends to be controlled by the lossiest, not the hardest, sediments. Thus, range-dependence generally leads to higher propagation loss than would be expected, due for example to lossy sediment patches and/or nulls in the reflection coefficient. In a few instances, propagation over a range-dependent seabed can be calculated using range-independent sediment properties. The theory may be useful for other (non-oceanic) waveguides.

Advanced Applications for Underwater Acoustic Modeling

“…They can also lead to very simple and intuitive expressions. This method has been extended for reverberation [134].…”

Predicting the Impact of Seabed Uncertainty and Variability on Propagation Uncertainty

“…• Developed an intuitive theoretical expression for propagation in a waveguide with rangedependent seabed properties, Ref [3]. The importance of the theory is that it provides some deep insights and predictive capability into how propagation uncertainties are controlled by seabed spatial variability.…”

Seabed Geoacoustic Structure at the Meso-Scale

“…Determining the impact of sediment meso-scale variability on propagation, reverberation and clutter will be addressed via modeling, both with simulated and measured meso-scale variability. The modeling builds on past work using energy flux methods (e.g., [1], [2]) along with PE and normal mode methods, in collaboration with Dale Ellis, (DRDC-A), Kevin LePage (NURC) and others.…”

“…Modeling studies employing the simulated meso-scale has the advantage of providing a deeper understanding of effects for a various canonical types of variability, accepting the disadvantage that since relatively little is known about the meso-scale, the simulation may or may not be representative of environments that actually exist. While there are some early insights into effects of meso-scale variability on propagation [2] in relatively simple environments, the more challenging problem of impact on diffuse reverberation and clutter needs to be addressed. The impact of meso-scale variability on clutter will be divided into two sub-classes, one where the meso-scale variability is so strong that it is essentially a discrete feature and produces clutter.…”