The deep-scattering layer is found in tropical waters at depths between 100 and 400 fathoms. In the Northern Hemisphere, the maximum volume reverberation occurs in March and the minimum in November. Bottom composition and roughness govern the degree of reverberation that contributes to the masking of target echoes. In theory, the amount of bottom reverberation is directly related to the roughness and com-position of the sea floor. However, the problem of bottom reverberation is a bit more complicated.
Scientists consider the ocean floor to be a two-dimensional volumetric scattering surface.
In other words, sound is not only reflected off the sea floor but also from formations of rock beneath the sea floor. Also, bottom roughness can be slight or great, and the wavelength component of the reflected sound can range from microns to miles. Another problem created at the ocean bottom is one of absorption. When the bottom is composed of soft mud, sound energy is absorbed. Absorption also occurs as sound propagates through the sea, and the energy is converted to heat.