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An Autonomous Underwater Vehicle for the Study of Small Lakes

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  • 1 Underwater Research Laboratory, School of Engineering Science, Simon Fraser University, Burnaby, British Columbia, Canada
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Abstract

A small autonomous underwater vehicle (AUV) was designed and built to carry a wide variety of oceanographic sensors in the relatively benign lacustrine environment. PURLII navigates along preprogrammed paths for up to 3 h using compass, depth, and acoustic altimeter information. A standard, off-the-shelf, self-recording CTD with pump was integrated into PURLII such that vehicle effects on data quality were minimized. An upper bound on temperature data resolution along the vehicle track was estimated to be 10 cm in the vertical and 35 cm in the horizontal. Five missions were conducted over the course of three days in a small lake approaching autumnal turnover. The goal was to obtain several “snapshots” of the temperature structure within the thermocline before and after a wind event. Each mission consisted of the AUV recording CTD data while moving up and down in a vertical sawtooth pattern and following a constant heading. At the end of an allotted period, PURLII would surface, turn through 180°, and repeat the sawtooth pattern while following a return heading to the start point. PURLII was able to complete 27 up and down profiles between 10 and 20 m over 1 km in 50 min. This provided enough temperature data to produce a vertical two-dimensional cross section of the temperature field, 1 km long and 10 m high. Temperature data measured with the AUV-mounted CTD compared favorably with that measured by conventional moored thermistor chains.

Corresponding author address: Bernard Laval, Centre for Water Research, Dept. of Environmental Engineering, The University of Western Australia, Nedlands, WA 6907, Australia.

Email: blaval@cwr.uwa.edu.au

Abstract

A small autonomous underwater vehicle (AUV) was designed and built to carry a wide variety of oceanographic sensors in the relatively benign lacustrine environment. PURLII navigates along preprogrammed paths for up to 3 h using compass, depth, and acoustic altimeter information. A standard, off-the-shelf, self-recording CTD with pump was integrated into PURLII such that vehicle effects on data quality were minimized. An upper bound on temperature data resolution along the vehicle track was estimated to be 10 cm in the vertical and 35 cm in the horizontal. Five missions were conducted over the course of three days in a small lake approaching autumnal turnover. The goal was to obtain several “snapshots” of the temperature structure within the thermocline before and after a wind event. Each mission consisted of the AUV recording CTD data while moving up and down in a vertical sawtooth pattern and following a constant heading. At the end of an allotted period, PURLII would surface, turn through 180°, and repeat the sawtooth pattern while following a return heading to the start point. PURLII was able to complete 27 up and down profiles between 10 and 20 m over 1 km in 50 min. This provided enough temperature data to produce a vertical two-dimensional cross section of the temperature field, 1 km long and 10 m high. Temperature data measured with the AUV-mounted CTD compared favorably with that measured by conventional moored thermistor chains.

Corresponding author address: Bernard Laval, Centre for Water Research, Dept. of Environmental Engineering, The University of Western Australia, Nedlands, WA 6907, Australia.

Email: blaval@cwr.uwa.edu.au

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