Backscatter signal formation in underwater lidar systems is studied and temporal and frequency characteristics are analyzed using the Monte Carlo technique. Both frequency and phase responses of the backscattered signal demonstrate similar dependencies, showing stronger frequency dependence in the high-frequency range. The beats of the frequency response due to dephasing of corresponding spectral harmonics are shown in the high-frequency range. Results of Monte Carlo simulations of the backscattered signal are in good agreement with the approximate analytical expression derived in the small-angle approximation; however, frequency responses calculated by the Monte Carlo technique and by small-angle approximation demonstrate a difference in the high-frequency range due to interference effects, while the phase response demonstrated good agreement in the entire frequency range.