The aim is to investigate the influence of the problem parameters and to search the procedures for decrease of the noises. The formulae for autocorrelation function of the echo-signal power, new model of the frequency-contrast characteristics, hardware procedure for decrease of the fluctuations, conditions of the high correlation (>.9) on the depth have been developedAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio