|Paper title||CFOSAT-base Swell Forecast System|
|Form of presentation||Poster|
Long-period swells generated in the North and South Pacific frequently hit the shores of low-lying Pacific islands and atolls. The accuracy of wave forecasting models is key to efficiently anticipate and reduce damage during swell-induced flooding episodes. However, in such remote areas, in situ spectral wave observations are sparse and models are poorly constrained. Therefore, Earth Observation satellites monitoring sea state characteristics, represent a great opportunity to improve the forecasting of flooding episodes, and the analysis of wave climate variability.
Here, we present a satellite-driven swell forecast system that can be applied worldwide to predict the arrival of swells. The methodology relies on the dispersive behavior of ocean waves, assuming that the energy travels along great circle paths with a celerity that only depends on its frequency. Satellite data for this analysis are directional wave spectra derived from SWIM acquisitions onboard the CFOSAT-mission (Hauser et al. 2021).
The proposed workflow includes: a) filtering the global-coverage data considering a temporal and geographical criterion (the spatial scale delimits the effective energy source that can reach the target location); b) comparison of wave parameters from CFOSAT-SWIM and partitions from a global wave numerical model for the removal of the directional ambiguity; c) definition of the spectral energy sector that points towards the study site; d) analysis of air-sea fluxes dissipation (Ardhuin et al. 2009); and, e) analytical propagation of the energy bins to forecast the targeted spectral energy over time.
Two examples of application are presented for the Samoa islands, and for the Cantabria coast (Spain). The time evolution of swell systems approaching the sites is evaluated against spectral energy from available in situ wave measurements and numerical model outputs. The results exhibit a good reproduction of the wave fields, proving the flexibility and robustness of the methodology.
The proposed method may be used to track swells across the ocean, forecast the arrival of swells or locate remote storms. For the Small Island Developing States, the output of the methodology can be undoubtedly of great help for stakeholders and decision makers to produce risk metrics
and implement strategies that minimize the vulnerability of these communities to coastal flooding at a very low computational effort.
This work was supported by the French National Research Agency through the ISblue program, (ANR-17-EURE-0015) and by CNES through the CFOSAT-COAST project.
Ardhuin, F., Chapron, B., & Collard, F. (2009). Observation of swell dissipation across oceans. Geophys. Res. Lett., 36 , L06607. doi: 10.1029/2008GL037030
Hauser, D. et al., (2021). New Observations From the SWIM Radar On-Board CFOSAT: Instrument Validation and Ocean Wave Measurement Assessment. IEEE Transactions on Geoscience and Remote Sensing 59, 5–26. https://doi.org/10.1109/TGRS.2020.2994372