Stochastic Forecasting of DriftingShips and Smaller Objects

Dr Øyvind BreivikNorwegian Meteorological Institute

Kjell RøangChristian Michelsen Research

Objective• To generate search areas for the Norwegian

Search and Rescue Service based on thebest available wind and current information

• Make search areas as small as possible, butnot smaller

Challenge

Other uses

• Containers• Mine-like objects• Objects at large (buoys, ROVs)

The Uncertainties Involved

• Where and when did the accident takeplace?

• Which object should we look for (life raft,person in water, …)?

• What are the wind conditions like in thearea?

• What are the surface currents in the area?

Search Maths

POS = POD x POC

• POS: Probability of success (do we findwhat we are looking for?)

• POD: Probability of detection (the keeneyes of the rescuers)

• POC: Probability of containment (are wesearching in the right place?), our business

Forces on a Drifting Object

• Wind (leeway)• Surface current• Wave motion (damping and excitation)

The motion of an object of arbitrary shape isdifficult to model, approximations areneeded

Wind to Wind to

WindDirection

From

WindDirection

From

Wind to

Lα = -25o Lα = +25o

RWD = -135o RWD = +135o

Leeway DriftDirection

Leeway DriftDirection

Leeway divergence

• Leeway divergencesends objects at an anglerelative to downwind

• Symmetry allows stabledrift left and right ofdownwind (little jibingis observed).

? Diverging search areaswith time

DownwindApproximations

Wind speed and object drift is approximatelylinearly relatedDifferent objects drift differently ...

Life raft with drogue

Undrogued life rafterror alexperiment

dσ

0 5 10 15 20 25−30

−20

−10

0

10

20

30

Wind Speed to 10−m height (m/s)

Cro

ssw

ind

Com

pone

nt o

f Lee

way

(cm

/s)

Maritime Life Rafts with Deep Ballast System and Canopy(4−6 person capacity)

RIGHT of DownwindLEFT of Downwind

CrosswindCrosswinderror alexperiment

cσ

0 5 10 15 20 25−20

0

20

40

60

80

100 O(100) ensemble of random maritime life raft drift properties

10 m wind speed [m/s]

Dow

nwin

d co

mpo

nent

of l

eew

ay [c

m/s

]

Empirical leeway modelEmpirical leeway model

' walk)(random windPerturbed

10 wWW +=

),0(onsperturbatileeway Constant

σε N∈

offset ,2/'slope ,10/'

εε

+=+=

bbaa

''[cm/s]leeway Crosswind

ccc baL ±±= W

''[cm/s]leeway Downwind

ddd baL += W

Archive and prognoses7 day archive combined with 60 h prognoses of• Wind from 20 km res. atmospheric model (HIRLAM 20)• Surface currents from 4 km res. ocean model with tides and wind forcing (POM)

Wind and current close upWind and current close up

AWI 0203

Longitude

Latit

ude

Drifting benthic lander, 2002−03−13T11 UTC to 2002−03−17T17 UTC

30’ 15oE 30’ 16oE 30’ 17oE 30’ 18oE

55’

72oN

5’

10’

15’

Ensemble mean trajectory

Observed trajectory

Pickup +104 h

Drift start 2002−03−13T11 UTC

13T12

15T0616T04

16T09

16T15

17T01

Icelandic exercise 2003

Longitude

Latit

ude

Iceland−Faroe exercise 2003−02−06T11 UTC to 2003−02−07T11 UTC

20’ 10’ 13oW 50’

42’

45’

65oN 48.00’

51’

54’

57’

Liferaft pickup +24 h

Convex hull of ensemble +24 h (search area)

Ensemble mean trajectory

Observed raft trajectory

Liferaft release position 2003−02−06T11 UTC

Faroe exercise 2004

Longitude

Latit

ude

Iceland−Faroe exercise 2004−05−03T22 UTC to 2004−05−04T14 UTC

30’ 15’ 12oW 45’ 30’ 62oN

10’

20’

30’

40’ Liferaft release position 2004−05−03T22 UTC

Liferaft pickup +16h

Convex hull of ensemble (search area)

Manual search areas

Operational use of LeeWay model

• Service operational from 2002• Simulation started by web order form• Result transferred by e-mail• Result presented in JRCC decision support

system SARA

System architecture

Wind and Current

DriftSimulator

Web order ResultPresentation

E-mail Transport

GRIB format

Web order, old

Web order, New

Results, sailboat

Results, PIW and Life raft

Other simulators

• Oil drift• Ship drift

Web order oil drift simulations

Oil drift

Web order, ship drift simulations

Ship drift, 1 simulation

Ship drift, ensemble model

Other services

• Weather forecasts overlay (MetOc)• AIS/VMS• Weather Observations

Weather forecast

AIS

Basestations PortsGraticule

Legend

Weather Observations

Weather Observations