Propagation of sound in the Arctic waveguide on extended path is accompanied both regular and stochastic scattering. The acoustic scattering on the statistically rough boundary ice cover excites stochastic component of sound pressure. It fluctuates relative to the mean level corresponding to the first statistical moment which is determined as a coherent (regular) component of sound pressure. The intensity of stochastic components corresponds to the dispersion of full sound pressure. The relation of energy intensities of coherent fields to the full ones is called as a coherence parameter. This parameter characterizes the fraction of stochastically scattered field in a full sound field. The phase pattern in a stochastic field is not stable in space and this is the reason why antenna devices response to the signal is unstable. The coherence parameter is relevant sound field characteristics and it is impossible without knowledge about it to estimate correctly the efficiency of extended antennae. The coherence parameter of a sound field usually decreases with rise of frequency and increasing of a distance to a sound source. However, in the Arctic waveguide, due to a peculiarity of vertical sound speed profile and presence of the ice cover irregularity, the coherence parameter of sound field firstly descends with increasing of a distance. Then on the definite spatial intervals the parameter increases as the frequency function, and at further increasing of a distance it again descends.
