Turbulence measurements from a submersible

Abstract

A Pisces submersible has been used to carry turbulence sensors through various mixing regimes in the coastal waters of British Columbia. Dissipation sales of kinetic energy and heat are suited to such a vehicles, as they are smaller than scales at which the submersible itself is moved by mean flows. In coastal waters, significant dissipation levels are associated with semi-deterministic flows (river plumes, tidal flows, internal hydraulic effects), which allow most efficient use of the limited time and space ranges typical of manned submersible operations. Major modifications necessary to stabilize the submersible for mid-water running, constraints on equipment, and present operational limitations are discussed. Advantages of a submersible over towed or self-propelled vehicles include lower vibrational contamination of velocity signals, slower mean forward speed, which places less strain on response of frequency-limited sensors, and extremely flexible operation, particularly close to the air-sea interface. These characteristics are documented with data obtained through an internal wave train and across the base of a river plume in coastal waters.