It is shown that the spectrum of a Gaussian surface has only the second-order rotational axis, and its moments of higher than the second order are degenerated in such a way that only three of them are independent and only two invariants are nonzero. The conditions for decomposition of the spectrum into one-dimensional systems are revealed, and the joint statistical distribution of the mean and differential curvatures at horizontal surface points is found. Within the framework of the Gaussian model, a simple optical method is suggested for simultaneous remote measurement of the second- and fourth-order invariants of spectral moments.