A Facility for Dynamic-Response Studies

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

0240956 Schmitt A large tank capable of long-term maintenance of a sharp temperature-salinity interface has been developed and applied to measurements of the dynamical response of oceanographic sensors. Matching the dynamic response of conductivity and temperature sensors has been a long-standing problem in the computation of salinity, and this tank offers a new approach to its solution. This project will improve the existing tank, evaluate a number of available CTDs., and provide improved algorithms for the estimation of salinity. The new tank uses a two-layer salt-stratified system 4.7 m deep that is heated from below and cooled from above. This generates two convectively mixed layers with a thin double-diffusive interface separating them. A temperature jump of 5-10 degrees C can be maintained over 1-2 cm (a vertical temperature gradient of order 103 degrees C/m) for ~2 weeks. A variable speed lowering system allows testing of the dynamic response of conductivity and temperature sensors in full-size oceanographic instruments. An acoustic echo sounder and an optical shadowgraph system provide non-disruptive monitoring of the interface and layer microstructure. Linear and nonlinear fitting routines have been developed to determine thermometer response times that are a strong function of the speed. A method for the optimal design of lag-correction filters, based on an imposed linearity of the conductivity-temperature relationship across the interface, has been developed to accurately match temperature and conductivity sensors for the computation of salinity. Sensor response characterization is especially important for autonomous instruments where data processing and compression must be performed in-situ, but is also helpful in the development of new sensors and in assuring accurate salinity records from traditional wire-lowered and towed systems. This project will implement a number of improvements to the tank, evaluate several existing CTDs, suggest improved algorithms for the computation of salinity and establish the tank as a dynamic response facility for use of the oceanographic community. The broader impacts of this work stems in part from its contributions to the pressing societal need for improved ocean observations for climate change research. Also, the dynamic response facility will be a community-wide resource for improving the state-of-the art in salinity observations for both the profit and non-profit sectors. Finally, it will continue to utilize and train graduate and undergraduate students in its operations.