Monitoring a lake by an underwater drone (glider)

Summary

The present report presents results from testing of an undulating underwater vehicle for environmental monitoring in a deep lake in Norway, Lake Hornindalsvatn, in October, 2013. A Slocum glider was used for the purpose. Some traditional measuring devices like lowered CTDs were applied as well, to collect data for comparisons. NIVA, The Norwegian Institute for Water Research, coordinated the project, with partners from University of Bergen, Runde Environmental Centre and PLOCAN (Spain). The tests were supported by the Norwegian Public Roads Administration, the Norwegian Environment Agency and the County Governor of Sogn og Fjordane county. The primary objective was to test the performance of the vehicle in terms of operability in such environment as a lake, surrounded by high mountains that might impair on the data transmission. The glider had incorporated some standard sensors for water quality like turbidity, chlorophyll and oxygen. The communication with the glider via satellite and Internet worked well, the mountains did not seem to reduce transmission quality. Control and operation of the glider worked out well, similar to operating offshore, but with more frequent interceptions during the short mission, to test out various modes and functions. The bottom sensing and autonomous dive abortion when approaching the bottom worked well. The glider wars operated in station mode profiling at a fixed position as well as making transects along the lake. Technically, the glider functioned well during the lake mission. Preliminary assessment of the collected water quality data indicated this sensing platform is quite as good as conventional measurement methods, and it has extra capacity to carry additional sensors. Monitoring of performance and data is done by a pilot on-shore. This can be a time-consuming task, but by sharing work between different pilots and centra operating many gliders, this can be accomplished cost-efficiently. The gliders have functions being activated in emergency situations, when they surface and send back status data. This can be useful when monitoring at a site where activities may cause some form of pollution temporarily, such as road construction. It was concluded that the tests with the limited scope were successful. It is recommended to study the possibilities for such use of autonomous vehicles on a national scale, more in-depth, and also to gather information on any experiences from other countries. It is indicated that for regular use in lakes, the gliders will have to be down-scaled in size, possibly be more modular to suit the actual purpose. Gliders are extensively used in ocean monitoring, and by selective adaptation there is a potential for a similar paradigm shift for lakes and fjords as well.