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A shore-based High-Frequency (HF) WERA radar was recently installed by Ocean Networks Canada (ONC) near Tofino, British Columbia (Canada), to mitigate the elevated tsunami hazard along the shores of Vancouver Island, from both far- and near-field seismic sources and, in particular, from the Cascadia Subduction Zone (CSZ). With this HF radar, ocean currents can be measured up to a 70-85 km range, depending on atmospheric conditions, based on the Doppler shift they cause in ocean waves at the radar Bragg frequency. In earlier work, the authors (and others) have shown that tsunami currents need to be at least 0.15-0.20 m/s to be reliably detectable by HF radar, when considering environmental noise and background currents (from tide and mesoscale circulation). This would limit the direct detection of tsunami-induced currents to shallow water areas where they are sufficiently strong due to wave shoaling and, hence, to the continental shelf. It follows that, in locations with a narrow shelf, warning times based on such a tsunami detection method may be small. To detect tsunamis in deeper water, beyond the shelf, the authors have proposed a new algorithm that does not require "inverting" currents, but instead is based on spatial correlations of the raw radar signal at two distant locations/cells located along the same wave ray, time shifted by the tsunami propagation time along the ray. A pattern change in these correlations indicates the presence of a tsunami. They validated this algorithm for idealized tsunami wave trains propagating over a simple seafloor geometry in a direction normally incident to shore. Here, this algorithm is further developed, extended, and validated for realistic case studies conducted for seismic tsunami sources and using the bathymetry, offshore of Vancouver Island, BC. Tsunami currents, computed with a state-of the- art long wave model, are spatially averaged over cells aligned along individual wave rays, within the radar sweep area, obtained by solving the wave geometric optic equation. A model simulating ONC radar's backscattered signal in space and time, as a function of the simulated tsunami currents, is applied on the Pacific Ocean side of Vancouver Island. Numerical experiments are performed, showing that the proposed algorithm works for detecting a realistic tsunami. Correlation thresholds relevant for tsunami detection can be inferred from the results. [ABSTRACT FROM AUTHOR]

The article discusses research which developed a general analytical framework to obtain the second-order Lagrangian solution for the gravity surface wave fields in a compact and vectorial form. Topics discussed include the classical second-order Eulerian expansion by Longuet-Higgins and comparison of the nonlinearities between Lagrangian perturbation expansion and Eulerian expansion.

The article discusses research which explored the use of numerical simulations of tsunami propagation and high frequency (HF) radar remote sensing to develop a tsunami detection algorithm. Topics discussed include the algorithm's computation of the correlation of HF radar signals and an analysis following the Tohoku 2011 tsunami in Japan which showed that the HF radars could be used to detect tsunami-induced currents and issue tsunami warning.

The article presents information on a study which examined the development of free surface reconstruction algorithms to predict ocean waves, based on spatial observations made with a high frequency Advanced Scientific Concepts (ASC) Inc. Flash light detection and ranging (LIDAR) camera. Nonlinear sea surfaces are represented using the Lagrangian model Choppy. The LIDAR camera parameter was adjusted down to a minimum configuration to validate the two-dimensional (2D) algorithms.