Development and Evaluation of the New RBRlegato3 CTD on Glider Platforms

Eric Siegel, Mark Halverson, Rui Zhang, Jean-Michel Leconte and Greg Johnson, RBR Ltd, Ottawa, ON, Canada
Building on long-term development for the Argo program, the RBRlegato3 CTD has been developed to improve measurements, enable longer missions, and reduce calibration down-time for ocean gliders. TheRBRlegato3 provides CTD measurements calibrated to WOCE specifications for accuracy and stability. TheRBRlegato3 measures conductivity using a rugged inductive cell that is not affected by surface contaminants or freezing conditions. The CFD-optimised, low aspect ratio conductivity cell is self-flushing and does not require a pump. Using only 72mW (6mA at 12V) when sampling at 2Hz or faster, and 18mJ/sample at 1Hz or slower, the power requirement is about 75% lower than traditional pumped CTD sensors. Totally silent operation is optimized for passive acoustic listening and turbulence measurements. The RBRlegato3 is designed to fit into a standard 2″ x 7″ sensor bay, with both wet-bay and dry-bay models, and is rated to 1000m. The presentation will report on RBR's collaboration with glider manufacturers and scientists including integration of the new CTD, development of dry-bay and wet-bay mechanical solutions, and performance in strongly stratified environments. RBRlegato3 CTD data is evaluated using QARTOD tests, nearby CTD profiles, and other glider CTDs. We focus specifically on sensor accuracy, but also analyze upcast/downcast pairs for evidence of dynamic performance in strongly stratified conditions.