1ACTIMAR – 24, quai de la Douane – F 29200 Brest - +33 (0)298 44 24 51 – www.actimar.fr

A SIMPLE OPERATIONAL MODEL

FOR THE ANALYSIS AND FORECAST

OF POLLUTANT AND OBJECT DRIFT

Philippe Craneguy

ACTIMAR(craneguy@actimar.fr)

Sea Tech Week – BrestTechnologies for Search, Assistance and Rescue

18-20 October 2004

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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 toolsOcean model - Trajectory diagnostic - Drag forces

Background (oil drift prediction)PREVIMEL + ARIANE

Extension towards object drift predictionIn test

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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)

PREVIMEL

Sea-surface horizontal velocity field(Ekman drift + wind entrainment)

Thermal structure of the mixed layer and the thermocline

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Weather Forecast Model

Data Assimilation Module Mixed Layer model FLORENCE 1D

Turbidity BathymetryBarotropic

tidalcurrent

Atmosphericparameters

Ocean SurfaceT°C files

(US NAVY)

AVHRRimagery(NOAA)

In-situmeasurements

Air-Sea Interface fluxes:

- Solar + IR radiation- Heat fluxes- Evaporation / Precipitation- Mvt amount flux from wind stress on the surface

Vertical 1DT° profile

Driving Current Fieldfrom surface wind

Ekman Currentfield

3D T°Analysis

field

InitialConditions

fieldDrift Current field

3D T°Forecast

field

Lagrangian path computing module ARIANE 2D

Operational Digital system foranalyzing and forecasting from J to J+3the thermal and dynamics behavior of

the ocean upper layer down to 400m depth

PREVIMEL

PREVIMEL

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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)

ARIANE

Lagrangian trajectories of sea-surface or subsurface particles derived from ocean model outputs

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Guiding principles

ARIANE

• 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

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Application to the Prestige oil drift prediction

PREVIMEL + ARIANE

Drift calculated from Previmel results(Ekman + 4% of the wind)

347° 348° 349° 350° 351° 352°

19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

347° 348° 349° 350° 351° 352°

Drift observed duringthe same period

Nov. 19 Dec. 23, 2002

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Application to the Prestige oil drift prediction

PREVIMEL + ARIANE

19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Multiple particles view

(Nov. 19 Dec. 23, 2002)

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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)

OBJECT DRIFT

Trajectories of objects at sea-surface or subsurface

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Force balance on free floating object

OBJECT DRIFT

Wind (Vatmos)

Oceanic current (Vwater)

Radiative waves

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

Resulting displacement

(Vobject)

With:ρa, ρw: density of air/waterSa, Sw: emerged/immersed surface of the objectCa, Cw: drag coefficient in the air/waterCiw: incident wave reflection coefficientA: wave amplitudeL: object length scaleg: gravitational accelaration

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Analytical solution

OBJECT DRIFT

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)]

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Task sequencing (24H set-up)

CONCLUSION

Vobject = Vwater + (Vatmos-Vwater).sqrt[(ρa.Ca.Sa)/(ρw.Cw.Sw)]

Weather Forecast Model (Worldwide)

PREVIMEL (1D-mixing model)

Vwater (drift) Vatmos (wind)

ARIANE 2D (lagrangian trajectories)

OBJECT DRIFT