Influence of non-uniform flow fields on imaging deviation of side-window airborne optical systems

The non-uniform flow field around high-speed flying vehicle “bends” the ray and imposes an imaging deviation on the imaging plane. This deviation seriously affects the airborne imaging applications. In this study, the factors that influence the imaging deviation are cataloged into two classes: the vehicle-related factors and the flow-field-related factors. Flow density computations are discussed. A backward ray tracing scheme is proposed. The imaging deviations, the propagation path distances in the non-uniform flow field, and the density distributions along propagation paths for a typical flight condition are investigated. Three flow-field-related factors should be considered in order to reduce the deviation: the propagation path distance in the non-uniform flow field, which should be as short as possible; the angle of incidence at the free stream boundary, which should be as small as possible; and the density distribution along the propagation path in the nonuniform flow field, which should be as flat as possible.