SPIE publishes accepted journal articles as soon as they are approved for publication Journal issues are considered In Progress until all articles for an issue have been published. Articles published ahead of the completed issue are fully citable.
A common method for synthesizing turbulent imagery is to model phase perturbations on a wavefront and then propagate the wavefront to the entrance pupil of an imaging system. The point spread function (PSF) that results from the wavefront in the pupil is then computed and used to synthesize images by the usual means of convolution. In a recent publication, a method was disclosed using sparse and redundant dictionaries of turbulent characteristics to construct PSFs directly in the image plane and simulate image formation without making phase models and computing wavefront propagation. However, the dictionary method, as disclosed in the recent publication, is limited to modeling PSFs characterized by the Fried parameter of the data used to construct the dictionary. Herein, we demonstrate that a dictionary constructed from data with a given Fried parameter can be scaled to construct turbulent PSFs corresponding to larger and smaller values of the Fried parameter. This enables a single dictionary, or a small number of dictionaries, to serve for the simulation of turbulent images over a range of turbulence conditions.
The history of the development of works on the creation of the elemental base of adaptive optics for a solar Russian telescope is briefly described. We consider separate issues of the development of the wavefront sensor (WFS) based on the Shack–Hartmann correlation sensor to provide measurements under conditions of strong turbulence. The parameters of the WFS are calculated on the basis of long-term observations of meteorological characteristics and optical measurements of the Fried parameter. A special adjusting device with a block of fast rasters changing is developed. The use of rasters of various dimensions is provided in the WFS. The sensor uses the original algorithm for determining the maximum of the correlation function. The effect on the accuracy of measuring the phase distortions of turbulence occurring in the rooms of the telescope itself is analyzed.
Deleterious effects of the atmosphere on remotely acquired images includes absorption and scattering of light by aerosol particulates, which not only attenuates the signal but can potentially cause blurring due to forward-scattered light accepted by the imaging system. Proposed aerosol scattering models (e.g., Ishimaru) provide a method for simulating the contrast and spatial detail expected when imaging through atmospheres with significant aerosol optical depth. This work explores closure between modulation transfer functions (MTFs) obtained from directly measured images and MTFs calculated from theory using measured cloud properties. The closure experiments are performed in a laboratory cloud chamber in which cloud droplet number density and size distribution are directly measured. Images of a binary knife-edge target were taken with an optical detector on the other side of a water cloud generated through reduction of pressure in the humidified chamber. The key results of this closure experiment are: the theoretical expression for the aerosol MTF is likely overly simplistic and does not account for broad particle size distributions. The significance of optical blurring from light scattering by aerosol particles depends sensitively on the properties of both the particles and the imaging system.