Remote sensing of radiation stress gradients from optical imagery Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/76537376r

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  • Wave-induced circulation is the defining characteristic of the nearshore. Within this region, the constant feedback cycle between incoming waves, wave-generated currents, and the mobile sediment bed is responsible for the evolution of complex patterns in nearshore and beach morphology. Central to our understanding of this system is knowledge of the forcing mechanisms. We investigate the potential of optical signals to provide an alternative remote sensing method for the direct estimation of radiation stress gradients in the nearshore. The use of an optical method will provide the ability to easily observe a large, spatially-dense array for extended periods. Additionally, the creation of a remote sensing technique will greatly expand the possibilities for data assimilation in nearshore circulation and sediment transport models. Here, we will examine the formulation of radiation stress gradients in terms of component variables with distinct optical signatures, as well as examine the relationship between optical radiation stress gradient measurements and in situ measurements of fluid response. Our results show that the spatial patterns in optical intensity due to wave breaking can be isolated from background optical intensity with a robust Gaussian breaker intensity model. However, the transformation from optical intensity due to wave breaking to a quantitative measure of local dissipation is quite complex. The use of in situ measurements of wave energy flux in calibration of this technique introduces a dependence on in situ instrumentation in an otherwise optical remote sensing technique. Normalized wave spectra are calculated based on pixel intensity time series from a 2-dimensional spatially-lagged array. These optical spectra compare well with spectra calculated from in situ puv data. The wave spectra provide a weighting term, allowing for wave frequency and directional spread. Results of each component model compare well with available field measurements, but validation of the complete optical radiation stress gradient technique is complicated by the lack of direct field measurements of radiation stress gradients. Attempts to examine the balance between wave-induced forcing and fluid response at the 1997 SandyDuck field experiment are complicated by the complex, non-linear nature of the current patterns during this deployment.
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