Comparison of ambient sound from 2000 m underwater with ground-based radar observations of rainfall

The underwater ambient sound generated by rainfall can be used to measure drop size distributions within the rain. These measurements allow detection, classification and quantification of rain and radar reflectivity factor. One of the advantages of the acoustical measurements is that the listening area, an effective "catchment" area, is proportional to the depth of the hydrophone. This feather allows high temporal resolution and a spatial averaging coverage comparable to a radar sampling volume. For the first time deep water acoustical measurements of rainfall are compared to high resolution ground radar reflectivities. The open sea measurements of underwater ambient sound were made from a sub-surface mooring near Methoni, Greece in 2004. The acoustical measurements were at 50, 200, 1000 and 2000 m depths. Simultaneous ground-based polarimetric X-band radar measurements were made over the acoustic mooring. Comparisons show acoustic detection of rain events and storm structure that are in agreement with the radar observations. Results from the comparison between the underwater sound pressure level at different depths and the radar reflectivity observations will be presented.