A Near-Surface Microstructure Sensor System Used during TOGA COARE. Part I: Bow Measurements

Abstract

High-resolution probes mounted on the bow of the vessel at a 1.7-m depth in an undisturbed region ahead of the moving vessel were used for microstructure and turbulence measurements in the near-surface layer of the ocean during TOGA COARE. The probes measured temperature, conductivity, pressure, three-component fluctuation velocity, and two components of acceleration. Accumulation of large amounts of high-quality near-surface data poses a difficult challenge, and deployment from the bow of a ship, such as is done with these sensors, requires rugged, well-calibrated, and low-noise sensors. The heaving motion of the ship that causes the sensors to break through the surface requires data processing algorithms unique to this application. Due to the presence of surface waves and the associated pitching of the vessel, the bow probes ?scanned? the near-surface layer of the ocean. Combining the bow sensor?s signals with the ship?s thermosalinograph pumping water from 3-m depth resulted in the near-surface dataset with both fine temporal/spatial resolution and high absolute accuracy. Contour plots calculated using the bow signals reveal the spatial structure of the diurnal thermocline and rain-formed halocline. The localization in narrow frequency bands of the vibrations of the bow sensors allows calculation of dissipation rates. The characteristics of the sensors and the data processing algorithms related to the periodic surface penetration by the sensors are discussed in this paper.