Prediction and exploitation: the use of the EOSTAR model in the marine infrared propagation environment

Modern surface Navy ships require dependable and predictable communications, surveillance, and tracking systems. An accurate model for the propagation of infrared and optical frequencies through the atmosphere is a requirement for these systems, which operate over long nearly-horizontal paths that are close to the land or sea surface. The determination of the propagation environment for surface ships can be a difficult problem. The most critical portion is the 50-meter-thick surface layer containing the ship and extending to the horizon. Extended horizontal propagation paths within this atmospheric surface layer encounter relatively dynamic refractivity conditions. We will describe the application of the EOSTAR (Electro-Optical Signal Transmission and Ranging) model suite to provide accurate sensor performance predictions. The EOSTAR model is built upon a geometrical optics approach to infrared propagation: a ray is traced through the propagation environment, and path-dependent perturbations to the signal can be determined. EOSTAR is a valuable tool for prediction and exploitation of several phenomena common to this environment, and we will discuss the design and use of three individual modules within the EOSTAR suite: 1. Exploitation of a sub-refractive mirage to provide a passive ranging capability; 2. A path-dependent calculation of a refractive propagation factor, or geometric gain; 3. Exploitation of scintillation effects to provide an early detection capability, and the prediction of a signature frequency and variance to enable detection enhancement.