Modeling solar eclipse shadow bands using wave optics simulation through distributed turbulence

Thin, wavy ribbons of light known as "shadow bands" can be seen moving and undulating on the ground just preceding and following the occurrence of a total solar eclipse. Using the scattering scintillation theory, Codona [Astron. Astrophys.164, 415 (1986)AAEJAF0004-6361] presented theoretical investigations that explain recorded features of shadow bands and suggest the turbulence mainly responsible for the bands is within the bottom 2-3 km of the atmosphere. This paper proposes an approach to model the shadow band phenomena using a numerical wave optics simulation. The simulation approach employs numerical wave optics techniques to model a crescent-shape source, propagation of component plane waves through turbulence phase screens, and observation of the light at the ground. The simulation produces intensity patterns with structures and evolution that are consistent with actual shadow band observations and Codona's theory. The contribution of the turbulence phase screens as a function of height to the shadow band intensity scintillation index is simulated and excellent correspondence is found with the theory. Finally, the practical utility of the simulation is illustrated by creating intensity frames that show the temporal evolution of the patterns due to wind. The simulation approach is adaptable and can be applied to scintillation and imaging problems involving other incoherent objects or sources that subtend relatively large angles and are observed through atmospheric turbulence.