Die Kuste, 81 (2014), 255-271 
259 
Figure 1: Maps and geographic information displayed in SeatrackWeb Java GUI. The blue area 
indicates depth values of the fine North and Baltic Sea grid of BSHcmod. Land as defined by the 
coastline is displayed in yellow. 
2.2 PADM 
PADM stands for Particle Advection and Dispersion Model and is die core of Seatrack 
Web calculating die advection of a substance or object by representing it by a cloud of 
particles (with the so called Lagrangian method). 
Each particle represents a certain amount of die simulated substance. The particles 
move individually in tiiree dimensions not affecting die surrounding flow field. Except 
for die gravitational spreading algoridim die particles do not influence each other (no 
collisions, etc.). When particles hit a boundary, like a coastline, die bottom or the bound 
aries of die model domain, it sticks to, slips along or passes tiirough diis boundary. Oil, 
for example, sticks at the coastline and at die bottom, while objects slip along diese 
boundaries. 
Each particle holds a part of the total mass and additional properties like viscosity, 
density, height, etc. The particle properties change due to substance specific processes. 
If for example oil is at die surface it evaporates depending - amongst otiiers - on 
temperature. 
The particles are placed in a grid widi rectangular, six-sided cells, where the x- 
direction tuns from west to east (longitude), die y-direction from soutii to nordi (latitude) 
and die z-direction points upwards. At die boundaries of die cells the x-, y-, z-velocities