Bispectral stellar image reconstruction: Image truncation, dynamic range, and object complexity

Abstract

Truncation of the speckle cloud by the edges of an image detector causes significant artifacts and distortions in images reconstructed from their second-and third-order spectra such as the Knox-Thompson (KT) and triple-correlation (TC) bispectra. At high signal levels the near-axis, TC transfer function has a lower phase variance than the KT transfer function. This gives TC a higher dynamic range, an important property when observing detail. In both cases, the amount of improvement in image quality obtained by using additional bispectral planes increases with object complexity. Examples illustrate these properties.

Speckle imaging of coherent sources

“…These simulations are performed by convolving random instances of 5.12 x 5.12 meter phase screens with the object field and intensity for coherent and incoherent imaging, respectively. The screens are generated by filtering Gaussian white noise with a modified Von Karman spectrum, 2 = O.O33C2 + 1)_U/6e (/5.92)2 illuminated. The magnitude of the reflectivity is portrayed in (a).…”