The U.S. Navy has a renewed interest in the use of high energy laser (HEL) systems for ship defense scenarios. Surface ships must track and engage targets within a thin near-surface environment called the marine atmospheric surface layer. Within this layer exist substantial gradients in temperature and momentum, thus making extinction and turbulence strong functions of height. In such an environment, a primary cause of beam degradation is the atmospheric composition along the beam path, and this problem is compounded by the vertical variations in extinction and turbulence.
The three primary effects that must be predicted for a successful system model are extinction, turbulence, and thermal blooming. Although these factors are present for any HEL scenario within the atmosphere, they are particularly prominent for the marine near-surface environment. Aerosol extinction can be a strong function of the near-surface path height when there are windy conditions, and this vertical dependence must be reflected in the model. The occurrence of turbulence along the path also degrades the on-target beam intensity, and this effect is also strongly height-dependent, with paths nearest the ocean-air interface encountering the greatest scintillation.
We will discuss our efforts to provide a useful irradiance-on-target envelope using existing models and meteorological databases to analyze the efficacy of an HEL system. An irradiance prediction for a HEL weapons system must be accurate and reliable since it will be impossible to perform appropriate field tests across the full spectrum of possible operational environments to be encountered by such a system.