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ACTIMAR – 24, quai de la Douane – F 29200 Brest - +33 (0)298 44 24 51 – actimar.fr

Detailed operational model for pollutant analysis, object drift forecast, and marine environmental protection, using weather forecasts and oceanic models for various applications such as search and rescue and navigation safety.

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ACTIMAR – 24, quai de la Douane – F 29200 Brest - +33 (0)298 44 24 51 – actimar.fr

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  1. A SIMPLE OPERATIONAL MODEL FOR THE ANALYSIS AND FORECAST OF POLLUTANTAND OBJECT DRIFT Philippe Craneguy ACTIMAR (craneguy@actimar.fr) Sea Tech Week – Brest Technologies for Search, Assistance and Rescue 18-20 October 2004 ACTIMAR – 24, quai de la Douane – F 29200 Brest - +33 (0)298 44 24 51 – www.actimar.fr

  2. INTRODUCTION • Aims of SURPOL model: • A simple and reliable drift model for any marine area • On the basis of available oceanic models and weather forecast • Easy and fast to implement for applications • Applications: • Marine Environmental Protection oil pollution at sea and to the coast, … • Search and Rescue persons in water, life rafts, … • Safety of Navigation, Recovery containers, debris, … • Development of the model • Gathering existing tools Ocean model - Trajectory diagnostic - Drag forces • Background (oil drift prediction) PREVIMEL + ARIANE • Extension towards object drift prediction In test

  3. PREVIMEL • Ocean model • 1D-vertical mixing (atmospheric fluxes, friction at the bottom) • Worlwide and easy to set up within 1 day for operational purpose • Weather Forecast Model (wind stress and speed, heat fluxes, …) • Remote data assimilation (SST) • In-situ data assimilation (XBT, buoys, …) • Reference: Gaspard (1990) • Sea-surface horizontal velocity field (Ekman drift + wind entrainment) • Thermal structure of the mixed layer and the thermocline

  4. PREVIMEL Atmospheric parameters Operational Digital system for analyzing and forecasting from J to J+3 the thermal and dynamics behavior of the ocean upper layer down to 400m depth Weather Forecast Model Air-Sea Interface fluxes: - Solar + IR radiation - Heat fluxes - Evaporation / Precipitation - Mvt amount flux from wind stress on the surface Ocean Surface T°C files (US NAVY) AVHRR imagery (NOAA) Barotropic tidal current In-situ measurements Turbidity Bathymetry Data Assimilation Module Mixed Layer model FLORENCE 1D Vertical 1D T° profile Ekman Current field Driving Current Field from surface wind Initial Conditions field 3D T° Analysis field 3D T° Forecast field Drift Current field PREVIMEL Lagrangian path computing module ARIANE 2D

  5. ARIANE • Trajectory tool - ARIANE • Based on non-divergence of flow • Water particles follow volume-preserving streamlines • Used here in a 2D-version at sea-surface or subsurface • Reference: Blanke & Raynaud (1997) • Lagrangian trajectories of sea-surface or subsurface particles derived from ocean model outputs

  6. ARIANE Guiding principles • First developed for tracking water masses 3D movements (origin and fate) • Based on the non-divergence of the flow • Volume conservation in elementary boxes on a C-grid (Arakawa, 1972) • Water particles follow volume-preserving streamlines • Non-crossing of the coastline or ocean bottom • Allows reverse trajectory calculations • Allows numerous multiple trajectories in order to represent the spreading of water patches

  7. PREVIMEL + ARIANE Application to the Prestige oil drift prediction Drift observed during the same period Nov. 19  Dec. 23, 2002 Drift calculated from Previmel results (Ekman + 4% of the wind)

  8. PREVIMEL + ARIANE Application to the Prestige oil drift prediction Multiple particles view (Nov. 19  Dec. 23, 2002)

  9. OBJECT DRIFT • Object drift – still in development • Adding drag coefficients for the immersed and emerged parts • Search and rescue issue • Reference: Allen and Plourde (1999), Breivik (2004) • Trajectories of objects at sea-surface or subsurface

  10. OBJECT DRIFT Force balance on free floating object Wind (Vatmos) Resulting displacement (Vobject) Oceanic current (Vwater) Radiative waves With: ρa, ρw: density of air/water Sa, Sw: emerged/immersed surface of the object Ca, Cw: drag coefficient in the air/water Ciw: incident wave reflection coefficient A: wave amplitude L: object length scale g: gravitational accelaration M.dVobject/dt = Fatmos + Fwater + Fwave Fatmos = ½.ρa.Ca.Sa.|Vatmos-Vobject|.(Vatmos-Vobject) = wind drag force Fwater = ½.ρw.Cw.Sw.|Vwater-Vobject|.(Vwater-Vobject) = water drag force Fwave = ½.ρw.g.Ciw.L.A2 = wave radiation force

  11. OBJECT DRIFT Analytical solution M.dVobject/dt = Fatmos + Fwater + Fwave • Assumptions and methodology • Steady state assumed at each lapse time → dVobject/dt = 0 • Fwave negligible for small objects (container, person in water, …)→ Fwave = 0 • Vatmos = wind speed given by Weather Forecast Model • Vwater = drift current given by Previmel • Ca,Cw: drag coefficients compiled by US Coast Guard (Allen and Plourde, 1999) • Trajectories calculated by Ariane with the solution of • ρa.Ca.Sa.|Vatmos-Vobject|.(Vatmos-Vobject) + ρw.Cw.Sw.|Vwater-Vobject|.(Vwater-Vobject) = 0 Vobject = Vwater + (Vatmos-Vwater).sqrt[(ρa.Ca.Sa)/(ρw.Cw.Sw)]

  12. CONCLUSION Task sequencing (24H set-up) Weather Forecast Model (Worldwide) PREVIMEL (1D-mixing model) Vwater (drift) Vatmos (wind) Vobject = Vwater + (Vatmos-Vwater).sqrt[(ρa.Ca.Sa)/(ρw.Cw.Sw)] ARIANE 2D (lagrangian trajectories) OBJECT DRIFT

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