Propagation of light through ship exhaust plumes

Abstract

Looking through the atmosphere, it is sometimes difficult to see the details of an object. Effects like scintillation and blur are the cause of these difficulties. Exhaust plumes of e.g. a ship can cause extreme scintillation and blur, making it even harder to see the details of what lies behind the plume. Exhaust plumes come in different shapes, sizes, and opaqueness and depending on atmospheric parameters like wind speed and direction, as well as engine settings (power, gas or diesel, etc.). A CFD model is used to determine the plume's flow field outside the stack on the basis of exhaust flow properties, the interaction with the superstructure of the ship, the meteorological conditions and the interaction of ship's motion and atmospheric wind fields. A modified version of the NIRATAM code performs the gas radiation calculations and provides the radiant intensity of the (hot) exhaust gases and the transmission of the atmosphere around the plume is modeled with MODTRAN. This allows assessing the irradiance of a sensor positioned at some distance from the ship and its plume, as function of the conditions that influence the spatial distribution and thermal properties of the plume. Furthermore, an assessment can be made of the probability of detecting objects behind the plume. This plume module will be incorporated in the TNO EOSTAR-model, which provides estimates of detection range and image quality of EO-sensors under varying meteorological conditions.