Surface wave effects on long range IR imaging in the marine surface layer

The quality of long range infrared (IR) imaging depends on the effects of atmospheric refraction and other pathintegrated effects (e.g., transmission losses, scintillation and blurring), which are strongly related to the prevailing meteorological conditions. EOSTAR is a PC based computer program to quantify these strong nonlinear effects in the marine atmospheric surface layer and to present a spectrally resolved target image influenced by atmospheric effects using ray tracing techniques for the individual camera pixels. Presently, the propagation is predicted with bulk atmospheric models and the sea surface is idealized by steady regular periodic Stokes' waves. Dynamical wind-waves interactions are not taken into account in this approach, although they may strongly modify the refractive index in the near-surface layer. Nonetheless, the inclusion of the sea surface in the ray tracer module already has a great impact on the near-surface grazing rays and thus influences the images especially in situations of super refraction and mirage. This work aims at improving the description of the sea surface in EOSTAR taking into account the non-uniformity of spatially resolved wind-generated waves and swell. A new surface module is developed to model surface wind-waves and swell in EOSTAR on the basis of meteorological observations and spectral wave modeling. Effects due to these new surfaces will be analyzed and presented.