The features of optical radiation interaction with surface of gratings are investigated. The diffraction grating is proposed to be used in the effective medium model to test nanostructured surfaces. This object allows obtaining simultaneous visualization of different spatial frequencies and estimation of both structure and surface features of 3D-objects. It was shown that the effective medium model could be used to predict the reflectivity of nanostructured surfaces by using diffraction gratings with different depths of profile. Computer simulations show that the filling factor of composite systems could be an angle dependent function. So, the correct solution of the inverse problem of finding surface characteristics, such as refraction indices and absorption coefficients, is related with the angle dependence of filling factor.