A miniature, low cost CTD system for coastal salinity measurements

In this work we describe a small, low cost conductivity, temperature and depth (CTD) system for measurements of salinity in coastal waters. The system incorporates three low cost expendable sensors, a novel planar four-electrode conductivity cell, a planar resistive temperature device and a piezoelectric pressure sensor. The conductivity cell and the resistive temperature device were fabricated using novel printed circuit board (PCB) microelectromechanical (MEMS) techniques combined with a new thin-film material, liquid crystal polymer (LCP). Printed circuit board techniques allow for mass production of the sensors, thereby lowering the cost of the system. The three sensors are packaged so that they are independent of one another and can be quickly replaced if bio-fouled or damaged. Deployments in Bayboro Harbor, St Petersburg, FL demonstrate that the novel CTD systems are capable of obtaining highly resolved in situ salinity measurements comparable to measurements obtained using commercially available instruments. The estimated accuracies for the conductivity, temperature and pressure sensors are +/- 1.47%, +/- 0.546. C and +/- 0.02 bar, respectively. This work indicates that a small, low cost CTD system with expendable/replaceable sensors can be used to provide accurate, precise and highly resolved conductivity, temperature and pressure measurements in a coastal environment.