  We have measured the amplitude and the phase of an electromagnetic (EM) field
radiated from superconductor (amorphous ZrTiCuNiBe alloy) in the mixed state
due to interaction of the flux lattice with an elastic wave. The results
undoubtedly point to an essential contribution of a surface pinning into the
flux lattice dynamics. We propose a model that describes radiation of EM field
from superconductors with non-uniform pinning. The model allows to reconstruct
the viscosity and the Labush parameters from the experimental data. The
behavior of the Labush parameter can be qualitatively explained in terms of the
collective pinning theory with the allowance of thermal fluctuations.
