Images measured through the atmosphere are degraded by scattering and absorption from aerosols along the path and by atmospheric turbulence. In the presence of heavy scattering at visible and infrared wavelengths, the distances over which reasonable observations are possible are quite short compared to astronomical imaging paradigms, and aerosol scattering effects dominate the degradation of the point spread function (PSF) due to atmospheric effects. In addition to aerosol-induced blurring, measurement noise effects are present in observed images. We examine the problem of reconstructing images degraded by aerosol blur and measurement noise using estimates of the overall PSF, which account for unscattered and scattered radiation detected by the imaging system. Representative images of a spoke target acquired under various conditions of scattering and photon flux levels were simulated, and reconstruction of the degraded images is performed using two linear reconstruction algorithms: a Wiener filter and a constrained least squares filter. Results of the reconstructions show that spatial resolution can be recovered in badly blurred images up to the limit imposed by the noise effective cutoff spatial frequency of the measurement.
The image spectrum signal-to-noise ratio (SNR) provides a means of estimating the noise effective spatial resolution of an imaging system and a means of estimating the highest spatial frequency which can be reconstructed with a postdetection image reconstruction algorithm. Previous work has addressed the effects of aerosol scattering on the overall point spread function (PSF). Here, we seek to extend these results to also account for the effects of measurement noise and to then estimate the noise effective resolution of the system, which accounts for scattering effects on the PSF and measurement noise in the detector. We use a previously published approach to estimating the effective PSF and radiometric calculations to estimate the mean numbers of direct and scattered photons detected by an imaging system due to reflected radiation in the visible and near-infrared, and emitted radiation in mid-infrared (MIR) band, for a horizontal near-ground imaging scenario. The analysis of the image spectrum SNR presented here shows a reduction in the value of noise effective cutoff spatial frequency for images taken through fog aerosol media, and hence emphasizes the degrading effect of fog aerosol models on the spatial resolution of imaging systems.