Current techniques for simulating light propagation through atmospheric turbulence employ Fourier transform methods for calculation of diffraction effects. Although highly accurate, these methods are computationally burdensome, and substantially slow the task of computing extended scenes on a time-varying basis, as is required for closed-loop analysis of laser weapons systems' performance. In other areas of computational wave simulation (fluids and electromagnetics) Fourier techniques have been replaced by specialized finite-difference techniques which offer comparable accuracy for substantially reduced computational cost. Alternatively, these same diffraction effects seem amenable to local solution by integral techniques which would also provide a speed-up over use of Fourier methods. Potential speed-ups for the diffraction portion of the simulations range from 6 to over 150. Both alternative methods handle general boundary conditions much more gracefully than Fourier techniques. LRK Associates proposes to adapt both the finite-difference and integral techniques to the scene propagation problem, testing their accuracy and measuring their computational advantages on some simple test problems. This will lead to recommendations on which techniques are the best candidates for implementation in the Phase II to replace Fourier transform techniques for this optical simulation application.
Benefits: There is an emerging commercial market for fast atmospheric propagation simulation as LIDAR imagers become more prevalent. LIDAR technology is being considered for imaging applications on projects such as BAMS, Firescout, Maritime Mission Aircraft, NASA planetary exploration spacecraft, Tomahawk, and other weapons' seekers. This results in a commercial need for accurate and efficient computer simulation of atmospheric effects. Additionally, there is a latent requirement for atmospheric effects simulation in the area of low-power, eye-safe, optical communication for Internet users, because of accuracy requirements. This is especially critical in enterprise applications, and for solving the "Last Mile" conundrum facing the telecommunications industry. In the 1990s many companies promoted free-space optical telecommunications concepts for urban areas, universities, and industrial campuses without properly considering atmospheric effects on signal scattering degradation and the safety of pointing/aiming errors. A fast optical simulation capability will provide the telecommunications industry with a tool to evaluate the magnitude and importance of these effects prior to installation, building confidence in the use of free-space communications techniques for these applications.
Keywords: atmospheric light propagation, diffraction effects, finite-difference, computational efficiency, integral methods
