Comparisons of remotely-retrieved directional wave spectra over a large area with a shoaling-wave model
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Validation and development of shoaling-wave models generally rely on measurements from buoys or pressure arrays to characterize the wavefield. However, these sensors provide single-point or localized measurements and do not give any insight into the transformation of the wavefield across the shoaling region. As such, a model that is adjusted for favorable comparison with these localized measurements could inadvertently misrepresent the wavefield in other regions of the shoaling area. Therefore, an investigation was undertaken to compare results of a shoaling wave model with large-area, remotely-sensed imagery of waves. Data for the study were provided by the Airborne Remote Optical Spotlight System - MultiChannel (AROSS-MC) during the Nearshore Canyon Experiment (NCEX) at Scripps Institution of Oceanography (SIO) in La Jolla, CA in the fall of 2003. AROSS-MC is four digital-framing cameras coupled with an integrated Global Positioning System/inertial measurement unit (GPS/IMU) mounted in a yoke-style, computer-controlled positioner, all on a small aircraft. The system is pointed at commanded aimpoints as the aircraft flies past and the system maintains a stable platform to provide time-series imagery of a common area of the ocean surface. Dwell time can be many minutes and coverage is approximately 7 km2 per individual collection. By varying the aimpoint of the system, data are collected over the shoaling region from deep water to the shoreline. Using the recorded camera location and attitude in the GPS/IMU data, each image is transformed to a rectilinear geodetic grid at the mean sea level. 3-D data cubes are constructed from these geo-rectified data and used to calculate 3-D -k radiance spectra. The gravity wave dispersion surface is located and a 1-D integral is performed to generate frequency-direction (f-d) spectra at various locations across the shoaling wave region. The measured wave spectrum at the Torrey Pines buoy in deep water is used to initialize a shoaling wave model (SWAN) and this is used to calculate equivalent f-d spectra at the same locations. The comparison between these model and empirical results is made to determine missing physics in the model.
