The article is devoted to the study of the adequacy of the model of a waveguide with a bottom in the form of half-space in broadband calculations of sound fields. Two bottom models are considered: liquid and porous. Two depths of the water layer are considered - units of meters and tens of meters. In the case of a liquid bottom, the speed of sound and the loss tangent in the bottom are considered to be frequency independent (model with a bottom with constant quality factor). In the case of a porous bottom, the frequency dependence of the speed of sound and the loss tangent is extracted from experimental data published in open sourses. The frequency dependences of the group velocities of the modes and modal attenuation coefficients are calculated. The frequency dependences of the group velocity of the first mode for the two waveguide models coincide, and the critical frequency of the normal modes changes in proportion to the depth of the water layer. The frequency dependences of the attenuation coefficient of normal modes turn out to be significantly different. The impulse response of shallow and deep-water waveguides are simulated. It is shown that in the case of a waveguide with a water layer depth of a few meters, the temporal structure of the impulsive field is indistinguishable - the bottom model without dispersion is adequate. In the case of a water layer depth of tens of meters, the temporal structure of the pulsed field for two bottom models is different - the waveguide model with a bottom without dispersion is inadequate.
Keywords: liquid bottom, porous bottom, marine sediments, dispersion of phase velocity, group velocity, intramode dispersion, intermode dispersion