Comparison of spatially varying optical and in-situ surf-zone currents during large wave events

Longshore surf-zone currents and wave-averaged motions have long been recognized as an important process within the surf zone, advecting large quantities of sediment. The relevance of such alongshore processes to the evolution of sandbar morphology remains a difficult distinction, especially considering large morphological change signals often occur during extreme waves events when the surf-zone is anomalously wide and in-situ measurements can be difficult to obtain. Numerous remote sensing techniques have been applied to obtain nearshore hydrodynamics, but with validations typically limited to the range of waves, tides, and winds occurring during short-term deployments. Motivated by the potential for alongshore current profiles to improve cross-shore morphologic models, we leverage long-term monitoring operations at the USACE Field Research Facility (FRF) as well as observations from the pilot deployment of the DUring Nearshore Event eXperiment (DUNEX) to constrain the range of conditions providing viable remotely sensed alongshore current estimates. Optical estimates are derived by observing sea foam drift on the water surface processed with Fourier transforms [Chickadel et al. 2003] and Radon transforms [Almar et al., 2016] of time series of alongshore transects extracted from coastal imagery. At the FRF, the Argus tower has six cameras that provide imagery capturing alongshore variability as well as the cross-shore gradients in longshore currents. Current meters deployed along a single cross-shore transect provide multiple stationary observations, while drifter deployments provide Lagrangian observations with spatial coverage for validation.