Underwater communication offers great challenges for the researchers due to its time variable channel. In recent literature many methods are proposed for tracking these time variable channels, however robust algorithms are required since there are situations where the actual ones fails without any obvious reason. In deep water the underwater communication channel is characterized by a long multipath spread where each of the paths is affected by different environmental variation. The Doppler spread function enables us to understand these changes by analysing instantaneous time spectrum variability. To study the effects of environmental variations an isolated path is analysed by computing its Doppler spread spectrum. By inspecting the Doppler spread spectrum for different time windows an interesting behaviour is observed which is expected to be due to surface waves. Surface waves affect the Doppler by shortening and stretching the path between the transmitter and receiver. In this paper we have processed CALCOMM’10 sea trial data which took place from 22nd to 24th of June at the south coast of Portugal.