The hydrographic Doppler sonar system on the Roger Revelle

Turbulent mixing rates in the sea have been found to vary as the fourth power of the fine scale (∼10 m) vertical shear. The global distribution of shear is poorly known, associated with phenomena which are potentially quite localized in space and time. With the construction of the R/V Roger Revelle it was deemed appropriate to develop an exploration-mounted Doppler sonar system for the global scale mapping of the fine-scale shear and velocity fields. Termed the Hydrographic Doppler Sonar System (RDSS), it consists of nested quartets of 50 and 140 kHz transducers, installed in two 4"×12\´ wells, one on either side of the Revelle\´s keel. Transmitting repeat sequence coded pulses through a 1" polyethylene window, the 50 kHz system profiles to depths of order 600-1000 m, with 18 m depth resolution. The 140 kHz system attains depths of 200-350 in with 4 in depth resolution. The HDSS has played a central role in experiments such as ASIAEX, EPIC and HOME, and has provided background information in a variety of other programs. The routine "steaming data" is enabling us to accumulate a growing picture of the global distribution of shear and associated underlying phenomena.