Image quality analysis of a spectra-radiometric sparse-aperture model

Abstract

Sparse aperture (SA) telescopes represent a promising technology to increase the effective diameter of an optical system while reducing overall weight and stowable size. Although conceptually explored in the literature for decades, the technology has only recently matured to the point of being reasonably considered for certain applications. In general, a sparse aperture system consists of an array of sub-apertures that are phased to synthesize a larger effective aperture. The models used to date to create predictions of sparse aperture imagery typically make use of a assumption, where the input is a resampled black and white panchromatic image. This input is then degraded and resampled with a so-called polychromatic system optical transfer function (OTF), which is a weighted average of the OTFs over the spectral bandpass. In reality, a physical OTF is spectrally dependent, exhibiting varying structure with spatial frequency (especially in the presence of optical aberrations or sub-aperture phase errors). Given this spectral variation with spatial frequency, there is some concern the traditional gray world resampling approach may not address significant features of the image quality associated with sparse aperture systems. This research investigates the subject of how the image quality of a sparse aperture system varies with respect to a conventional telescope from a spectra-radiometric perspective, with emphasis on whether the restored sparse aperture image will be beset by spectral artifacts.