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Principal research goals are to characterize the physics and fluid dynamics which exist at the Mouth of the Columbia River. Coming from the relatively benign environment of the New River Inlet (RIVET I), this DRI will provide much stronger flows, larger waves, and more dynamic signals for our remote sensing instruments to observe. A by-product of the observational program will be the development of sensing capabilities that may have Naval interest.

Our long term goals are to improve our ability to characterize and forecast ocean surface waves. Most all at-sea Naval operations depend on knowledge of the conditions of the sea surface in one form or another. This includes the forecasting of EM/RF propagation near the ocean-surface as sea surface roughness has a profound influence on transmission characteristics. The world s oceans are data poor with respect to in-situ wave observations that are suitable for assimilation into, and verification with, operational global wave models (WAM, WaveWatch III). Data that is routinely available to models are satellite-based and have their own set of challenges. For example, remote sensing of the surface wave field using techniques such as radar altimetry or synthetic aperture radar (SAR) provides some measure of bulk wave properties, such as significant wave height or mean wave direction, and can be used to adjust global wave models. However, the techniques suffer from several issues: poor spectral resolution (e.g., differentiating swell vs. seas); the estimation of wave height is dependent on semiempirical models or modulation transfer functions that have inherent errors: and the satellite repeat time over a particular region of the ocean is too long to reliably improve. Global wave models suffer additional challenges as the wind forcing terms are derived from models (COAMPS, NOGAPS) that have their own set of data sparse challenges, and wave-current interactions are typically neglected due to poor measurements of ocean surface currents.

Full scale measurements of wave impact loads and their statistics in real sea states are desirable for validation of numerical simulations and for application to marine engineering design problems. Measuring and/or estimating wave forces on flat plates are especially problematic due to statistics of large waves in a given sea state, the intermittent statistics of wave breaking, the sensitivity of the loading relative to the phase of the incoming wave and scaling issues when translating from model scale data to full-scale. To increase our understanding of wave hydrodynamic pressures on a flat plate, an instrumented plate was deployed from the Scripps Institution of Oceanography's research pier. The instrumented plate is exposed to a wide range of wave conditions with a significant wave height (Hs) ranging from 3-4 m in the winter and Hs in the 1-2 m range in the summer. The instrumented flat plate is composed of three discrete modules each containing 6 pressure gages. Data are being collected over an extended period, nominally 12 months, to characterize extreme value distributions due to wave impact loading. Preliminary analysis of the data is presented and discussed.

Due to difficulties and uncertainties in accurately representing the bubbly flow around a ship in a laboratory facility, there is a need for full-scale (or near full-scale) measurements of bubbly flows generated around surface ships. These needs are parallel to components of ONR's ship hydromechnics program (Free-Surface Phenomena and Two-Phase Flows) which "...seeks to understand the physical mechanisms underlying interactions of two-phase water flow around ships and in their wakes with the air/sea boundary, and to incorporate that information in a computational fluid dynamics flow solver."

This report describes the research performed on behalf of the Office of Naval Research to understand the influence of air-sea interaction processes on hyperspectral remote-sensing of the ocean's surface. The Hyperspectral Coupled Ocean Dynamics Experiment (HYCODE) and Monte Carlo Radiative model were used to investigate these processes, as well as newly refined acoustic techniques. A byproduct of this research will be models to correct for bubble mediated effects in measured hyperspectral light fields using wind and wave information. The program also presented an opportunity to develop techniques for inverting remotely-sensed hyperspectral imagery for in-situ bubble concentrations.

The long-term goals of this research are to improve our knowledge and understanding of the role of breaking in air-sea interaction. We are concerned with the role of breaking in the fluxes of momentum, energy (mechanical and heat) and mass (gasses & aerosols) across the air-sea interface. These processes are important for the generation of ocean currents, air-sea heat and gas transfer , surface-wave evolution and dissipation, upper ocean mixing and transport, and hurricane dynamics (Melville, 1996).