Bathymetry is a major factor in determining nearshore and surf zone wave transformation and currents, yet is often poorly known. This can lead to inaccuracy in numerical model predictions. Here bathymetry is estimated as an uncertain parameter in a data assimilation system, using the ensemble Kalman filter (EnKF). The system is tested by assimilating several remote sensing data products, which were collected in September 2010 as part of a field experiment at the U.S. Army Corps of Engineers Field Research Facility (FRF) in Duck, NC. The results show that by assimilating remote sensing data alone, nearshore bathymetry can be estimated with good accuracy, and nearshore forecasts (e.g., the prediction of a rip current) can be improved. This suggests an application where a nearshore forecasting model could be implemented using only remote sensing data, without the explicit need for in situ data collection.

Thermal infrared (IR)-based particle image ve locimetry (PIV) is used to measure the evolution of velocity, turbulent kinetic energy (TKE), and the TKE dissipation rate at the water surface in the tidally influenced Snohomish River. Patterns of temperature variability in the IR imagery arise from disruption of the cool-skin layer and are used to estimate the 2-D velocity field. Comparisons of IR-based PIV mean velocity made with a colocated acoustic velocimeter demonstrate high cor relation (r² >; 0.9). Over a tidal period, surface TKE computed from the IR velocity varies from 10^-4 to 3 × 10^-3 J · kg^-1, with an average difference from the in situ measurements of 8%. IR-derived TKE dissipation rates vary from approximately 3 × 10^-6 to 2 × 10^-4 W · kg^-1 at peak ebb, agreeing on average to within 7% of the in situ velocimeter results. IR-based PIV provides detailed measurements of previously inaccessible surface velocities and turbulence statistics.

Surface disruptions by boils during strong tidal flows over a rocky sill were observed in thermal infrared imagery collected at the Snohomish River estuary in Washington State. Locations of boil disruptions and boil diameters at the surface were quantified and are used to test an idealized model of vertical boil propagation. The model is developed as a two‐dimensional approximation of a three‐dimensional vortex loop, and boil vorticity is derived from the flow shear over the sill. Predictions of boil disruption locations were determined from the modeled vertical velocity, the sill depth, and the over‐sill velocity. Predictions by the vertical velocity model agree well with measured locations (rms difference 3.0 m) and improve by using measured velocity and shear (rms difference 1.8 m). In comparison, a boil‐surfacing model derived from laboratory turbulent mixed‐layer wakes agrees with the measurements only when stratification is insignificant.

Thermal infrared (IR) imagery is used to quantify the high spatial and temporal variability of dissipation due to wave breaking in the surf zone. The foam produced in an actively breaking crest, or wave roller, has a distinct signature in IR imagery. A retrieval algorithm is developed to detect breaking waves and extract wave roller length using measurements taken during the Surf Zone Optics 2010 experiment at Duck, NC. The remotely derived roller length and an in situ estimate of wave slope are used to estimate dissipation due to wave breaking by means of the wave‐resolving model by Duncan (1981). The wave energy dissipation rate estimates show a pattern of increased breaking during low tide over a sand bar, consistent with in situ turbulent kinetic energy dissipation rate estimates from fixed and drifting instruments over the bar. When integrated over the surf zone width, these dissipation rate estimates account for 40–69% of the incoming wave energy flux. The Duncan (1981) estimates agree with those from a dissipation parameterization by Janssen and Battjes (2007), a wave energy dissipation model commonly applied within nearshore circulation models.

Sea Surface Temperature (SST) modifies the turbulent mixing, drag, and pressure gradients within the marine atmospheric boundary layer that accelerate near‐surface flow from cool to warm SST, and decelerates the flow from warm to cool SST. This phenomenon is well documented on scales of 100 − 1,000km (the oceanic mesoscale), however, the nature of this air‐sea coupling at scales on the order of 1 − 10km (the submesoscale) remains unknown. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) can be used to study submesoscale phenomena because the high resolution infrared and near infrared images can used to estimate both SST and wind speed. Observations of dramatic temperature and wind gradients along the Gulf Stream landward edge are used to examine the surface wind response to submesoscale fronts in SST. Our analysis indicates that SST‐induced wind speed perturbations are observed at the scales of order 1 − 10km, significantly smaller than previously suggested.