  Stochastic gravitational waves (SGW) can be detected by measuring a
cross-correlation of two or more gravitational wave (GW) detectors. In this
paper we describe an optimal SGW search technique in the wavelet domain. It
uses a sign correlation test, which allows calculation of the cross-
correlation significance for non-Gaussian data. We also address the problem of
correlated noise for the GW detectors. A method that allows calculation of the
cross-correlation variance, when data is affected by correlated noise, is
developed. As a part of the optimal search technique a robust estimator for
detector noise spectral amplitude is introduced. It is not sensitive to
outliers and allows application of the search technique to non-stationary data.
