  We study an observational method to analyze non-Gaussianity of a
gravitational wave (GW) background made by superposition of weak burst signals.
The proposed method is based on fourth-order correlations of data from four
detectors, and might be useful to discriminate the origin of a GW background.
With a formulation newly developed to discuss geometrical aspects of the
correlations, it is found that the method provides us with linear combinations
of two interesting parameters, I_2 and V_2 defined by the Stokes parameters of
individual GW burst signals. We also evaluate sensitivities of specific
detector networks to these parameters.
