1. Forecasting Drifting Objects
Dr Øyvind Breivik
Norwegian Meteorological Institute
Norwegian Meteorological Institute

2. Norwegian Meteorological Institute
Objective
To generate search areas for the Norwegian Search and Rescue Service based on the best available wind and current information
Challenge
To paraphrase Einstein:
Make search areas as small as possible, but not smaller
Norwegian Meteorological Institute

3. The Uncertainties Involved
Where and when did the accident take place?
Which object should we look for (life raft, person in water, …)?
What are the wind conditions like in the area?
What are the surface currents in the area?
Norwegian Meteorological Institute

4. Norwegian Meteorological Institute
Search Maths
POS = POD x POC
POS: Probability of success (do we find what we are looking for?)
POD: Probability of detection (the keen eyes of the rescuers)
POC: Probability of containment (are we searching in the right place?), our business
Norwegian Meteorological Institute

5. Forces on a Drifting Object
Wind (leeway)
Surface current
Wave motion (damping and excitation)
The motion of an object of arbitrary shape is extremely difficult to model, thus approximations are needed
Norwegian Meteorological Institute

6. Norwegian Meteorological Institute
Empirical leeway data
63 classes of SAR objects have been compiled by the U.S. Coast Guard through extensive field campaigns and were generously made available to the project.
Norwegian Meteorological Institute

7. Norwegian Meteorological Institute
Approximations
Wind speed and object drift is approximately linearly related
Different objects drift differently
Approximations
Undrogued life raft
Life raft with drogue
Norwegian Meteorological Institute

8. Norwegian Meteorological Institute
Leeway divergence
Objects drift at an angle to the wind (the leeway divergence angle)
Symmetry allows stable drift left and right of downwind.
This leads to a diverging search area as time progresses
Norwegian Meteorological Institute

9. Norwegian Meteorological Institute
Forcing
Wind from 20 km res. atmospheric model (HIRLAM 20)
Surface currents from 4 km res. ocean model with tides and wind forcing (POM)
Archived winds and currents go 7 days back – forecasts up to +60 h
Norwegian Meteorological Institute

10. Search areas and ensemble modelling
A search area is found by computing an ensemble of trajectories with slight changes in
drift properties
wind field
initial position & time of incident
Individual trajectory
Norwegian Meteorological Institute

11. Norwegian Meteorological Institute
leeway.met.no
Search area simulations are ordered via the web
Results are returned to the Rescue Co-ordination Centres and presented as a layer on an electronic sea chart
Norwegian Meteorological Institute

12. Norwegian Meteorological Institute
Bjarne – RCC test dummy
Regular exercises
Daily tests
Norwegian Meteorological Institute

13. Norwegian Meteorological Institute
Icelandic exercise 2003
Norwegian Meteorological Institute

14. Ensemble search area (10nm x 10nm)
Liferaft release position
Manual search areas
Ensemble search area (10nm x 10nm)
Liferaft pickup +16h
Faroe exercise May 4th 2004
Norwegian Meteorological Institute

15. The flora of SAR objects
Redo older leeway categories with new field methods
Refine the taxonomy for different parts of the world – in close collaboration with RCCs
Norwegian Meteorological Institute

16. Fedje – a potential testbed
Three HF radars
currents
wave measurements
Weather station
8 km wave model
4 km ocean model
Drifters (IMR)
Norwegian Meteorological Institute

17. Norwegian Meteorological Institute
Conclusions & outlook
The model yields realistic search areas, but further model evaluation is needed (more field campaigns) to thoroughly assess its forecasts capabilities for specific S&R objects
More leeway categories are needed to cover the range of typical S&R objects found in Norwegian and European waters
Error model for estimating uncertainties in winds and currents should be improved
Norwegian Meteorological Institute