排序方式： 共有4条查询结果，搜索用时 40 毫秒
1
1.
Current models used to predict the backscattering strength of the ocean floor are either very involved, requiring geoacoustic parameters usually unavailable for the site in practical applications, or overly simplistic, relying mainly on empirical terms such as Lambert's law. In any case, solutions are very approximate and the problem is still far from being solved. In this paper, a model is presented that avoids empirical functional forms yet requires only a few physical parameters to describe the surficial sediments, often tabulated for typical sediments. The aim of this paper is to develop a simple algorithm for operational prediction of bottom reverberation with only one free parameter, i.e., the volume scattering coefficient. The algorithm combines a two scale surface scattering model with scattered contributions originating from inhomogeneities within the sediments, talking into consideration the rough interface. No specific mechanism is assumed for scattering at the volume inhomogeneities; however, the inhomogeneities are assumed to be uniform and isotropic. The volume scattering coefficient, combined with the bottom attenuation and density and referenced to the surface, plays a role similar to the Lambert's constant in empirical models. The model is exercised on a variety of published datasets for low and moderately high frequency. In general, the model performs very well for both fast and slow sediments, showing a definite improvement over Lambert's law 相似文献
2.
When modeling sound propagation through the uppermost layers of the ocean, the presence of bubble clouds cannot be ignored. Their existence can convert a range-independent sound propagation problem into a range-dependent one. Measurements show that strong changes in sound speed and attenuation are produced by the presence of swarms of microbubbles which can be depicted as patchy clouds superimposed on a very weak background layer. While models suitable for use in acoustic calculations are available for the homogeneous bubble layer (which results from long time averages of the total bubble population), no similar parameterizations are available for the more realistic inhomogeneous bubble layer. Based on available information and within the framework of a classification scheme for bubble plumes proposed by Monahan, a model for the range and depth dependence of the bubbly environment is developed to fill this void. This model, which generates a possible realization of the bubbly environment, is then used to calculate the frequency-dependent change in the sound speed and attenuation induced by the presence of the bubble plumes. Time evolution is not addressed in this work 相似文献
3.
An upgrade to bistatic scattering strength modelling that is based on the authors' current understanding of bottom topographic scattering with an emphasis on modeling the `forward lobe' where Lambert's law fails quite significantly is reported. Low-frequency bottom scatter modeling is reviewed with particular emphasis on the issues of the forward scattered lobe. A specific model (a modified version of BISSM) is proposed, and the model's advantages and limitations are discussed. The requirement for certain high-resolution geomorphic data needed to support the model is discussed. Like the original BISSM, the version does not modify the accepted form for diffuse scattering, but it does modify the form of the forward lobe 相似文献
4.
Scattering from the ocean bottom is often assumed to be controlled by two spatial scales: the larger scale associated with reflections from plane facets, and the smaller one associated with diffuse scattering from height variations. Choosing the wavenumber for this partitioning has proven to be important but troublesome. For this work, scattering data are simulated using Helmholtz-Kirchhoff or physical optics theory and selected input geomorphology. These data are inverted to provide rms slope of facets and rms heights of small-scale roughness using a simple two-scale roughness model introduced previously (J. W. Caruthers and J. C. Novarini, IEEE J. Oceanic Eng., vol. 18, pp. 100-106, 1993). Bottom relief is described by power spectra of the power law form, and the bottom is assumed to be impenetrable. The work introduces a new criterion for effecting this partition based on setting a roughness parameter equal to unity. The criterion is shown to be valid for the cases analyzed based on the ability of the inversion model to recover the input geomorphology 相似文献
1