Laboratory Evaluation and Control of Slocum Glider C–T Sensors

Abstract

naccounted transient or permanent changes in sensor performances can compromise the overall quality of datasets obtained with a glider. From the specific perspective of the principal physical variables (temperature and conductivity), the main short-term risk is the deterioration of the quality of salinity data that is primarily due to the fouling of the glider?s conductivity sensor, especially when the glider approaches the sea surface and is deployed in coastal waters. Another potential short-term risk is a sudden shift in the glider?s temperature response caused by the blanketing of the temperature sensor by extraneous material. The long-term risks are the intrinsic drifts of the two sensors as specified by the sensor manufacturer. Given the way a glider operates, it is practically impossible to obtain sufficiently representative temperature and salinity samples in the field for effective comparisons with sensor data. Hence, laboratory testing of the temperature and conductivity sensors is one approach used to estimate the qualitative changes in pre- and postdeployment sensor performance in order to mitigate measurable drift effects on the collected data. This paper presents a systematic procedure that can be used to conduct reproducible laboratory evaluations of the temperature and conductivity sensors on a Teledyne Webb Research (TWR) Slocum glider. It is shown that the data from such tests can give useful information regarding the data quality as a result of fouling of the sensors during missions. Obviously, this kind of information is valuable when the reliability of mission-generated temperature and conductivity data, which are used to determine salinity, have to be assessed.