Cross spectrum analysis applied to speckle interferometry

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Abstract
The authors show, theoretically and experimentally, that a cross spectrum analysis allows an unbiased estimate of the image Wiener spectrum to be obtained. This unbiased estimation is obtained without altering the signal to noise ratio, provided that the real part of the cross spectrum is used as the estimate of the power spectrum. The technique is based upon the use of a dual channel experiment, each of the channels giving a record of the image intensity with a specific noise: the cross spectrum technique suppresses the background shot noise, because the noise is uncorrelated from one channel to the other. The experimental results are shown to be in good agreement with theory. The observations were run during May 1982 at the 193 cm telescope of the Haute Provence Observatory (France), using alpha Boo (Arcturus) as a reference point source star.