Acoustical Properties of Mud Sediments
Abstract : Goals include the development of models and methods that explain observed material and acoustic properties of different physical types of shallow-ocean mud sediments. Other goals are to assess prior data relating to the acoustic properties of mud and to provide guidance in the development and interpretation of experiments. A related goal is to construct models that will guide inversion techniques for inferring properties of mud sediments, for estimating accuracy of results, and for use in applications. These goals are science relevant to resolving long-term Naval problems of transmission loss and array response in shallow water over mud sediments and of acoustic detection, localization, and classification of objects buried in mud. Develop analytical fundamental-physics models for geoacoustic properties that show their dependence on mud parameters. Properties include material density, porosity, and compressional and shear sound speeds and attenuations, with focus on depth and frequency dependence. Estimate the accuracy of physical mud parameters that is required for acoustic data comparisons and for making predictions in applications. Use modeling results to provide methodologies for inversion methods in order to determine parameters and profiles in mud sediments.
Role of binding energy (edge-to-face contact of mineral platelets) in the acoustical properties of oceanic mud sediments
A theory for mud sediments presumes a card-house model, where the platelets arrange themselves in a highly porous configuration; electrostatic forces prevent face-to-face contacts. The primary type of contact is where the edge of one platelet touches a face of another. Why such is not also prevented by electrostatic forces is because of van der Waals (vdW) forces between the molecular structures within the two platelets. A quantitative assessment is given of such forces, taking into account the atomic composition and crystalline structure of the platelets, proceeding from the London theory of interaction between non-polar molecules. Double-integration over both platelets leads to a quantitative and simple prediction for the potential energy of vdW interaction as a function of the separation distance, edge-from-face. At moderate nanoscale distances, the resulting force is attractive and is much larger than the electrostatic repulsion force. But, at very close (touching) distances, the intermolecular force ...
The Earth's Angular Momentum Budget on Subseasonal Time Scales
Irregular length of day (LOD) fluctuations on time scales of less than a few years are largely produced by atmospheric torques on the underlying planet. Significant coherence is found between the respective time series of LOD and atmospheric angular momentum (AAM) determinations at periods down to 8 days, with lack of coherence at shorter periods caused by the declining signal-to-measurement noise ratios of both data types. Refinements to the currently accepted model of tidal Earth rotation variations are required, incorporating in particular the nonequilibrium effect of the oceans. The remaining discrepancies between LOD and AAM in the 100- to 10-day period range may be due to either a common error in the AAM data sets from different meteorological centers, or another component of the angular momentum budget.