The parameters of an echo signal from the underwater lidar are studied for the case of modulation of a probing pulse by a high frequency signal with a frequency linearly varying with time. The analysis is based on the statistical Monte Carlo simulations of the frequency and phase responses of a signal propagating along the emitter-water-reflector-water-receiver path and an analytical representation of the signal as a pulse described by a Gaussian function with intrapulse modulation. Delays and pulse shape changes caused by temporal dispersion of the photon-density waves are estimated. It is shown that the temporal dispersion effect reduces the efficiency of the matched processing of a complex signal in the receiving system.