Tsunami detection by High Frequency Radar using a Time-Correlation Algorithm: performance analysis based on data from a HF radar in British Columbia

摘要

A High-Frequency (HF) radar was installed by Ocean Networks Canadain Tofino, BC, to detect tsunamis from far- and near-field sources onthe Pacific Ocean side of Vancouver Island; in particular, from seismicsources in the Cascadia Subduction Zone. Based on a classical analysisof the Doppler spectrum, this HF radar can measure ocean surface currentsup to a 85-110 km range depending on sea state. However, an inherentlimitation of detection of small and short-lived tsunami currents is theconflicting requirement for short integration time and sufficient accuracy(resolution) of the Doppler spectra. This limits a direct tsunami detectiontypically to shallow water areas over the continental shelf where tsunamicurrents have become sufficiently strong due to wave shoaling.To overcome this limitation, the authors have recently proposed a newdetection method, referred to as “Time-Correlation Algorithm (TCA)”,that does not require inverting Doppler spectra for the tsunami currentsand can thus potentially detect an approaching tsunami in deeper water,beyond the continental shelf. This algorithm is based on computingspace-time correlation of the raw radar signal in different radar cellsaligned along precomputed tsunami wave rays, and time-shifted by theprecomputed tsunami propagation time between cells. A change in patternof such correlations indicates the presence of a tsunami. They validatedthe TCA with numerical simulations for both idealized (Grilli et al.,2016a) and realistic (Grilli et al., 2016b, 2017) tsunami wave trains andseafloor bathymetry, using data simulated with a radar simulator.