This paper presents a theoretical study of sound wave propagation through media whose properties change along one of the coordinate rectangular axes, and remain constant in the plane orthogonal to this axis. The uppermost sea bottom layer could be modeled as such an inhomogeneous medium where the density, sound velocity, and absorption of acoustical energy varies along one axis. The results were applied to obtain the reflection coefficient of the water-bottom surface considering that there is a transitional inhomogeneous layer with density, velocity, and absorption gradient, and without discontinuity with the bottom. It was concluded that the reflection coefficient of the bottom surface shows a frequency variation, dependent on the physical property gradients in the uppermost sea bottom layer.