An operational search and rescue model for the Norwegian Sea and the North Sea

Abstract

A new operational, ensemble-based search and rescue model for the Norwegian Sea and the North Sea is presented. The stochastic trajectory model computes the net motion of a range of search and rescue objects. A new, robust formulation for the relation between the wind and the motion of the drifting object (termed the leeway of the object) is employed. Empirically derived coefficients for 63 categories of search objects compiled by the US Coast Guard are ingested to estimate the leeway of the drifting objects. A Monte Carlo technique is employed to generate an ensemble that accounts for the uncertainties in forcing fields (wind and current), leeway drift properties, and the initial position of the search object. The ensemble yields an estimate of the time-evolving probability density function of the location of the search object, and its envelope defines the search area. Forcing fields from the operational oceanic and atmospheric forecast system of The Norwegian Meteorological Institute are used as input to the trajectory model. This allows for the first time high-resolution wind and current fields to be used to forecast search areas up to 60 hours into the future. A limited set of field exercises show good agreement between model trajectories, search areas, and observed trajectories for liferafts and other search objects. Comparison with older methods shows that search areas expand much more slowly using the new ensemble method with high resolution forcing fields and the new leeway formulation. It is found that going to higher-order stochastic trajectory models will not significantly improve the forecast skill and the rate of expansion of search areas.

An ILP and simulation model to optimize search and rescue helicopter operations

“…Abi-Zeid and Frost (2005) design a geographical decision support tool that applies search theory to determine the optimal search plan for the Canadian Forces in case of missing aircrafts, while Wysokiński et al (2014) develop a similar system that is concerned with the missing person's behavior for the Polish SAR teams. Breivik and Allen (2008) present a stochastic trajectory model which concerns motions of drifting objects and use it for the Norwegian Sea and the North Sea. Although the above-mentioned tools and systems support SAR operations in terms of maximizing detection probability of missing objects, they are not appropriate for allocation of SAR resources.…”

OpenDrift v1.0: a generic framework for trajectory modeling

“…Further, both position and time may be provided as two-element vectors to seed elements continuously in space and time from position P1 with uncertainty radius R1 at time T1, to position P2 with uncertainty radius R2 at time T2. This is a common use case in search and rescue modeling (see Breivik and Allen 2008): a ship is 215 known to have departed from position P1 at time T1 with normally small uncertainty radius R1, and disappeared on the way towards the destination (P2), normally with larger uncertainty in position (R2) and estimated arrival time (T2). Thus, this will track out a 'seeding cone' in space and time.…”

“…-drifting objects for search and rescue (Breivik and Allen, 2008;Breivik et al, 2011Breivik et al, , 2013 -ichtyoplankton transport (fish eggs and larvae) for stock assessments (Röhrs et al, 2014) -microplastics suspended in the ocean (van Sebille et al, 2012(van Sebille et al, , 2015 25 Table 1 lists some commonly used trajectory models and their applications. Additionally, many individual researchers or research groups have been developing trajectory model codes for in-house use, without publishing (or naming) a software code.…”

A strategy for producing refined currents in the Equatorial Atlantic in the context of the search of the AF447 wreckage

“…Drifting objects are divided into classes, e.g., a person in water (PIW), various classes of life rafts, small motor boats, etc. (Allen and Plourde 1999;Breivik and Allen 2008), each object having a particular set of parameters for leeway calculation. In this study, the currents are used in two ways by MOTHY: the currents are prescribed either at the surface (and MOTHY just adds the wind drag on the emerged part of the objects) or just below the Ekman layer (at an around 30 m depth).…”