Abstract
AbstractOne of the major fields of application of speckle-interferometric and speckle-imaging techniques is the photometry of astronomical objects exhibiting structure smaller than the seeing limit. The accuracy of the photometry depends critically on the accuracy to which the modulation transfer function (MTF), that describes the atmospheric-telescopic attenuation of the Fourier amplitudes of the object under consideration, is known. The estimation of the effective MTF is especially difficult when no known reference object is within the field of view.A method is presented that allows to estimate the effective MTF from the observation of arbitrary structure with the use of FRIED-KORFF theory. The ratio of the squared modulus of the average Fourier transform and the average power spectrum serves as an estimator for the FRIED parameter r0. To a first approximation, this ratio is independent from the observed object. Additionally, the behaviour of the ratio in regions beyond the seeing limit in the Fourier plane may be analyzed to obtain an estimate of the speckle interferometry signal-to-noise ratio. The basic concept of the ratio method will be described, its accuracy will be discussed. First results on the application of the ratio method to observations of solar granulation will be presented.
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