Abstract: Results of observation of low-frequency tone pulse reverberation in deep open ocean by means of the combined sensor are presented. As the experiment showed, net energy flux density vector of the echo-signal carries information on properties of scattering directionality. The paper shows that the energy flux density vector of the field of surface – scattered low-frequency sound has both random and regular contributions. The regular contribution can be identified as the diffraction spectrum of scattered sound that is in line with the theory developed by L. Brekhovskikh. Lifetime of regular orderly structures existing in surface roughness is no less than 96 s as the experiment proves. The surface roughness diffraction lattice is likely to be built of swell waves.