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Speckle in Imaging Through the Atmosphere

Emphasis in the previous chapters has been on speckle that arises either from scattering from rough surfaces or scattering from diffuse volumes. In this chapter, attention is devoted to a different kind of speckle, namely, intensity fluctuations in the image of a distant incoherent object when the light from that object has propagated through random inhomogeneities associated with atmospheric turbulence. When the exposure or detection time is short compared with the fluctuation time of those inhomogeneities, atmospherically induced speckle is observed in the image. An explanation of the origin of this phenomenon will be given in the following subsections. Unlike discussions of speckle in previous chapters, which assumed reasonably monochromatic light, the speckle of interest here can occur in relatively broadband light, although if the bandwidth is too large the speckles can begin to wash out. In addition, since propagation through atmospheric turbulence does not change the polarization of the light, the speckle of interest here will be independent of polarization.