1 actimar – 24, quai de la douane – f 29200 brest - +33 (0)298 44 24 51 – a simple...
Post on 18-Dec-2015
221 Views
Preview:
TRANSCRIPT
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
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 toolsOcean model - Trajectory diagnostic - Drag forces
Background (oil drift prediction)PREVIMEL + ARIANE
Extension towards object drift predictionIn test
3
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
4
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
5
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
6
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
7
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
8
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)
9
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
10
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
11
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)]
12
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
top related