The underwater sound field can be used to quantify oceanic processes that actively produce sound, including, for example, wind/wave breaking (wind speed) and rainfall. These ``active'' sound sources are subsequently modified by the acoustic environment. In the case of wave breaking or rainfall, the sound source is located at the ocean surface. One of the principal features of the near-surface zone in the ocean capable of modifying the sound field is the ambient bubble field. Frequency-dependent modifications of the underwater sound field during heavy rainfall are observed. Using a rainfall generated sound field as an example, the change in the spectral character of the sound field will be used to quantify the formation and decay of an ambient bubble field. Documentation of the formation of a bubble layer has implications for gas and momentum exchange at the ocean surface by rainfall.