The inter-level correlation of the horizontal wind velocity have been estimated based on the data of acoustic sounding of the atmospheric boundary layer in different regions. The relation of the correlation to the type of stratification, the separation between levels, observation intervals, and the time of data pre-averaging has been analyzed. It has been shown, in particular, that the inter-level correlation under the convective conditions is higher than in the case of stable stratification. Sodar observations have been compared with the data of other authors.