Deploy, retrieve, repeat – made easy with RT 6 acoustic release
Deploying, locating and retrieving seabed sensors can be a challenge. Choosing reliable sensors that will work for the whole duration of the deployment and provide robust reliable results is just the start.
If you then want to retrieve and then redeploy them back at exactly the same site, you have an additional layer of complexity, especially if that site has significant tidal range and current regime.
This is just what independent physical oceanography consultancy DynamOcean has been doing in the Rance estuary in Brittany, France. The Rance estuary – where the River Rance enters the English Channel – has one of the largest tidal range in France, with an average of 8 m between low and high tide. During spring tides this figure can jump to as high as 13.5m!
DynamOcean’s aim has been to measure current, waves and turbidity in the Rance estuary using an acoustic Doppler current profiler (ADCP). This is to study sediment transport through the estuary. The measurements are being taken over six months, with recovery and re-deployment of the ADCP – in exactly the same position – every two months. This requires both a reliable acoustic release and also accurate seabed positioning in real-time.
For this project, DynamOcean chose our RT 6-1000 acoustic release transponder. This choice was guided by several years’ experience in using our Lightweight Release Transponder (LRT) and deciding to upgrade to our newer RT 6-1000. This is our entry-level release transponder with features that are far from entry-level, including 1,000 m depth rating, 15-month battery life, optional rope canister and – crucially – a release mechanism that will not let you down.
Alongside the RT 6-1000, DynamOcean is using a Micro-Ranger 2, Sonardyne’s smallest USBL system.
It’s easy to setup and use – even from a RIB or uncrewed surface vessel (USV) – and enables tracking of up to 10 targets out to 995 m range. For this project, it means DynamOcean can instantaneously position its seabed ACDP platform and also inspect it using a mini-ROV, which can also be positioned via a Nano beacon using the same Micro-Ranger 2 topside.
The set up
Because the RT 6-1000s (and all our family of release transponders), Nano and our Ranger USBL systems all work with the same 6G platform, they can be used interchangeably and seamlessly. This is just one of the benefits DynamOcean’s managing director Eloi Droniou explained when he told us about the set up for the Rance estuary project:
“The RT6-1000 integrated within a pop-up buoy on the seabed platform has multiple purposes,” he says, “one, release the pop-up buoy for the recovery of the seabed platform without the need for divers at the end of the measurements; two, measure inclination to make sure the platform is more or less level; and three, position accurately the seabed platform using various Sonardyne 6G topside options.
“With the release of Micro-Ranger 2 and Mini-Ranger 2, DynamOcean was thrilled to be able to not only instantaneously position the seabed platform but also to inspect it using a mini ROV, itself positioned using the lightweight and compact Nano transponder.”
“This allows us to make sure that it has landed properly, without needing any divers,” adds Droniou. “If the landing location is not satisfactory, the seabed platform can be raised from the seabed and moved to another nearby location. The seabed platform can also be inspected with the mini ROV just before releasing the pop-up buoy with the RT 6-1000 to check that everything is in order and verify the instrument’s height above seabed.
“Having the positions of the vessel, the seabed platform and the mini ROV, simultaneously and on the same survey window (Ranger 2 software), is essential for these operations.”
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