Abstract: The article presents the theoretical analysis and the results of numerical calculations of the Doppler effect it occurs in a system designed to determine the position and speed of a moving target. The transmitter is the source of the signal and it emits a sinusoidal, acoustic and continuous wave. Signal reflected off a moving target is received by four hydrophones. Based on the signals, four Doppler shifts are determined and inserted into a set of equations. The solution gives instantaneous target coordinates and the vector of target speed. Analytical formulas are given which describe the spectra of the Doppler shift of echo signals in a bistatic system, as well as numerically determined examples. Spectral lines are assigned to instantaneous target positions. This provides the basis for solving the above set of equations and the functioning of the system.