THE INFLUENCE OF THE ERRORS OF
SURFACE CURRENTS FIELD PROBABILITY
DISTRIBUTION ON SEARCH AREA
DETERMINATION
Burciu Z.
Gdynia Maritime University, ul. Morska 81-87, 81-225 Gdynia, Poland
Abstract: Determination of search area is one of the most important tasks during SAR action at
sea. According to the generally accepted methods [2] the most probable area in which the search object could be found is calculated for the hydro-meteorological conditions existed at the moment of accident. In fact the history of the on scene conditions has a significant influence on the developed surface currents field. The paper presents the influence of the errors of surface currents field probability distribution on search area determination.
1. Introduction
The generally accepted methods of search area determination and the guidelines of International Maritime Organisation (IMO) [2] are based on hydro-meteorological data existed at the moment of accident.
The most important factors influencing the accuracy of search area determination are the surface currents field parameters. Therefore the history of wind changes which the surface current velocity and direction are dependent on can not be neglected. The errors of surface currents field probability distribution have a significant influence on the position of search object as well as the dimensions of search area.
2. Determination of search area
The guidelines of Search and Rescue Manual adopted by IMO in 2002 [1] recommend the method of search area determination which does not consider the surface currents field, it’s dynamics, speed and direction. The method is based on hydro-meteorological data existed at the moment of accident.
It is very important to notice that the influence of surface currents can not be neglected because they are the most important elements determining the leeway of search object. An example of search areas for different hydro-meteorological conditions preceding a sea accident determined using the probabilistic method developed at Gdynia Maritime University based on Fokker–Planck model is presented in figure 1 [1].
Fig. 1. Search areas calculated for different hydro-meteorological conditions preceding a sea accident
3. Classes of search areas
The field of surface currents is formed under the influence of wind during a period of time dependent on wind parameters and the characteristics of the sea area. The surface currents fields observed by the author during sea investigations carried out in the South Baltic let to formulate conclusions regarding the classes of search areas in dependence on wind speed [1].
Class I is determined for the wind speed greater than 30 knots. The increase of search area due to the formed surface currents field is bigger in the direction parallel to the wind direction. An example of class I of search area is presented in figure 2.
Class
Class
I
I
II
II
V
V
ww
18
18
kts
kts
.
.
Class
Class
II
II
18<
18<
V
V
ww
30
30
kts
kts
.
.
Class I
Class I
V
V
ww>30
>30
kts
kts
.
.
Fig. 2. Search area - class I determined for wind speed Vw > 30 knots [1]Class II is determined for the wind speed greater than or equal to 18 knots and less than or equal to 30 knots. The increase of search area due to the formed surface currents field is bigger in the direction perpendicular to the wind direction. An example of class II of search areas is given in figure 3.
Class
Class
I
I
II
II
V
V
ww
18
18
kts
kts
.
.
Class
Class
II
II
18<
18<
V
V
ww
30
30
kts
kts
.
.
Class I
Class I
V
V
ww>30
>30
kts
kts
.
.
Fig. 3. Search area - class II, determined for wind speed 18
Vw
30 knots[1]Class III is determined for the wind speed less than 18 knots. The increase of search area due to the formed surface currents field is equally parallel and perpendicular to the wind direction. An example of class III of search area is presented in figure 4. In the case of change of wind speed or direction the change of position and dimensions of search area in comparison to the search area determined for the currently existed wind conditions follows from the influence of surface currents field probability distribution and the classes of search areas determined for the period preceding a sea accident.
Class
Class
I
I
II
II
V
V
ww
18
18
kts
kts
.
.
Class
Class
II
II
18<
18<
V
V
ww
30
30
kts
kts
.
.
Class I
Class I
V
V
ww>30
>30
kts
kts
.
.
Fig. 4. Search area - class III, determined for wind speed Vw < 18 knots [1]
Table. 1. Possible variantsof occurrence of search areas changes
No. Before accident After accident Search area determined in the first stage
1. Class I Class II Moved back, increased
2. Class I Class III Moved back, increased
4. Class II Class III Moved back, increased
5. Class III Class I Moved forward, decreased
6. Class III Class II Moved forward, decreased
The parameter characterizing the above cases is the time necessary for the change of surface currents field characteristics (change of class of search area). The time necessary for the change of surface currents field parameters Tp is described below,
Tp =f (K1, K2, ΔVw, Δ Kw,) (1) Tp = Tp1 + Tp2 + Tp3 + Tp4 +…+ Tpn (2) where:
K1 – class of surface currents field before accident, K2 – class of surface currents field after accident, ΔVw – change of wind speed per time unit, ΔKw – change of wind direction.
Fig. 5. An example of changes of parameters of a real surface currents field with the transfer from class III to class I
Fig. 6. An example of changes of parameters of the surface currents field for class I without a transfer from class III
Tp1 Tp2 Tp3 Tp4 Tpn
Kl III Kl I
Tp1 Tp2 Tp3 Tp4 Tpn
Fig. 7. Comparison of surface currents field parameters for class I and for the transfer from class III to class I. The search area is increased and moved back
4. Conclusions
The proper determination of search area requires the detailed information about the on scene hydro-meteorological conditions before the accident. Surface currents field should be treated as a random field due to the random character of environmental conditions influencing it’s parameters. As it has been presented in the paper the proper choice of probability distribution of surface currents field is very important for the proper search area determination. Therefore it is one of the most important factors influencing the time to search and the chances of finding and rescue survivors.
References
1. Burciu Z.: Modelowanie Obszarów Poszukiwania w Aspekcie Bezpieczeństwa Transportu Ludzi na Morzu. Prace Naukowe Transport z.50, Oficyna Wydawnicza Politechniki Warszawskiej, s.128, Warszawa 2003.
2. Provisions of conventions, plans, manuals and other documents affecting SAR – Changes to the IAMSAR Manual (First Edition). Proposed by the United States ICAO/IMO-JWG/7-WP.1 February , 2000. Adoption of amendments to the International Aeronautical and Maritime Search and Rescue Manual, MSC/Circ.999-11 June 2001.
