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15 September 2021

Alseamar, a producer of glider UUVs, has been able to produce highly accurate data plots of current profiles from large swathes of the water column. A combination of tailor-made algorithms, underwater gliders and a high-performing ADCP from Nortek has helped break new ground for the oceanographic community, making high-quality data more accessible for a multitude of stakeholders.

Acoustic Doppler current profilers (ADCPs) have revolutionized our ability to record ocean current movements. But they can only measure what they can "see”, and that is largely determined by what they are attached to, which may be a surface buoy or a frame on the seabed.

That’s perfect for many uses, but if you are seeking to find out about the movements of currents across a large swathe of ocean, then moving ADCPs on frames from location to location is a time-consuming business and doesn’t provide a complete picture of the currents in the whole area. Mounting an ADCP on a moving surface vessel is a good option for many, but some users are put off by the work and cost involved with hiring and crewing a vessel.

An efficient and cost-effective way to profile a large volume of water

However, rapid advances in underwater glider technology have provided an exciting new alternative. Slimline battery-powered gliders are capable of cruising through the oceans for months at a time, carrying a multitude of instruments measuring many facets of the underwater world close up.

Typically, gliders move in a sawtooth, or wave-like, movement between the top of the water column and depths of around 1000 m. So, if you can get accurate measurements from an ADCP fixed to a glider, you have an efficient and cost-effective way to profile a huge volume of water in a relatively short period of time.

That possibility prompted researchers at French marine tech company Alseamar to investigate how an ADCP could be made to work with their SeaExplorer glider. The company produces high-tech marine and submarine equipment, such as gliders (or UUVs – underwater unmanned vehicles) with very long mission endurance.

The results of Alseamar’s innovative development are of benefit for the greater ocean science community. The detailed analysis of current movements made possible by the Nortek ADCP, combined with data from the glider’s other instruments, gives users access to highly accurate data on how our oceans work.

"Glider missions contribute to the international efforts of the Global Ocean Observing System (GOOS),” says Orens de Fommervault, oceanographer at Alseamar.

The UNESCO-led GOOS program coordinates observations in the ocean globally, focusing on three critical themes: climate, operational services and marine ecosystem health.

Making water velocity measurements with glider-mounted ADCPs more accessible

Nortek’s 1 MHz current profiler was an attractive option for Alseamar due to a multitude of reasons.

"The Nortek ADCP design is really ideal for a profiling platform like ours. You could almost say it was dedicated to our application,” says Orens de Fommervault, who is the oceanographer at Alseamar leading the ADCP glider integration project.

This project truly breaks new ground in the oceanographic research industry. Some select academic institutions are also able to estimate water currents from a glider, but the real step forward is that this is now available as a service from a private company. Alseamar is currently the only known private company able to estimate water currents from a glider and to provide this service to other companies, organizations and researchers.

"Glider-mounted ADCPs offer the ability to collect high-resolution, dense-data water velocity measurements at an unprecedented spatio-temporal scale resolution without the constant use and expense of support vessels,” de Fommervault points out.

The relatively small size and low power consumption of Nortek’s ADCP are also plus points when you are seeking to pack as much instrumentation on to a glider as possible and get the most out of its on-board battery.

The ADCP-equipped glider has proved its accuracy in a number of different environments.

Current profiles obtained by the ADCP on the SeaExplorer glider across 60 km in the Mediterranean Sea off southern France correlate with temperature, salinity and chlorophyll measurements taken by the glider at the same time. The ADCP was also able to measure tidal currents in considerable detail through the depth profile in the Atlantic off northwest France.

Accurate analysis of currents across tens of kilometers of ocean is now possible due to Alseamar’s successful integration of the Nortek ADCP into its SeaExplorer glider. This provides unprecedented opportunities for measuring full ocean current profiles, whether the vehicle is ascending or descending.

Improving access to ADCP glider data in real time

But configuring the ADCP-equipped underwater glider to gather vast amounts of usable oceanographic data is not the end of the story.

"One big remaining challenge is to get access to as much of that data as possible in real time – something that is vital for our customers in the oil and gas industry, for example,” Orens de Fommervault says.

Alseamar has made considerable progress with this already, and is currently working to improve real-time data interpretation still further, de Fommervault says.