Evaluation of Metal-Film Temperature and Velocity Sensors and the Stability of a Self-Propelled Research Vehicle for Making Measurements of Ocean Turbulence

Abstract

Metal-film temperature and velocity sensors are being added to the Applied Physics Laboratory's Self-Propelled Underwater Research Vehicle (SPURV) to extend its measurement capability to turbulence scales. Before making field measurements, the sensors are being evaluated in the laboratory and the vibration level of SPURV is being measured to evaluate its stability as a platform from which to make turbulence measurements. The vibration is measured along the three major vehicle axes (vertical, horizontal, and longitudinal) using accelerometers. Field measurements were made with the accelerometers and the records integrated to obtain velocity spectra which are compared with typical measurements of ocean turbulence. The vehicle's motion is below the turbulence spectra when ocean turbulence dissipation is above 10^{-4} ergs/cm3/s, except at a multiple of the motor rotation frequency where the vibration appears as a strong peak. Electronics for remote operation of the metal-film temperature and velocity sensors were developed. To evaluate the sensors and electronics, test facilities were built for both static and dynamic calibrations. A temperature-controlled bath is used for static temperature calibrations. A submerged jet mounted within the temperature bath is used for static velocity calibrations. A thermal plume tank is used for dynamic temperature response calibrations of both the temperature and velocity sensors. The dynamic velocity calibration is made by oscillating the sensor within the static jet with a shaker pot. Results of these tests show that the sensor frequency response can be adequately determined, and that it extends to high enough frequencies to resolve turbulence fluctuations. The temperature sensor's noise and drift are low enough that good temperature measurements to turbulence scales can be made. However, poor stability and high noise in the velocity sensor make the measurements unreliable, and more work is being done in an attempt to improve the sensor.