Abstract: The propagation experiment of explosive sounds in the isothermal layer below the thermoeline was made, the record of individual modes for frequencies 0.32-1.0 kHz was obtained. By analyzing the travel time of mode pulse, it was determined that the oscillographic recording was the first mode. On the basis of analyzing the propagation properties of the first mode, the bottom-reflection coefficients at small grazing angle for frequencies 0.32-1.0 kHz were obtained.