This technological campaign has three objectives that require different equipment and skills. This campaign has therefore to be carried out in three parts.

The first leg is dedicated to bathymetric mapping using AUV. The next two legs are based on this mapping and are devoted to the maintenance of the acoustic positioning beacon field (leg 2) and to the intervention of the HROV on site for equipment control and interoperability tests for the installation and recovery of scientific equipment (leg 3).

Mission 1:

The installation of infrastructure and equipment on the seabed requires knowledge of the seabed, particularly in terms of bathymetry and the presence of possible obstacles that could damage cables or equipment. The AUV campaigns in 2018 and 2019 were not carried out because of partial work permits and bad weather conditions carried, for this reason, the 2020 campaign is devoted to the surveys that have not been carried out, i.e. the mapping of the infrastructure area and the MEUST cable route, and will have to be completed in 2021 to obtain data on the entire area to be instrumented and on the route of the 2nd cable, currently serving the ANTARES observatory and which will be routed back to the EMSO-KM3NeT IR after the dismantling of ANTARES.

The presence of a 4th AUV operator is necessary for a realtime data processing.

After the operation, the data are processed to provide a geo-referenced bathymetric map and a list of detected events and their location.

A ROV visual survey operation is required after the mapping to identify the events located by the AUV.

Mission 2:

The installation of KM3NeT detection lines and EMSO multidisciplinary instruments on the MEUST/NUMerEnv underwater infrastructure area is carried out by laying at the end of a deep sea cable at the targeted geographical point under the control of a precise Long Base acoustic positioning. This is done using an iXblue RAMSES Distancemeter installed on the surface vessel coupled to the ship's GPS and a Hydrins inertial unit. During operations, the packages to be deposited are positioned in real time by the RAMSES system with metric accuracy by acoustic triangulation with 4 autonomous acoustic reference beacons anchored around the MEUST/NUMerEnv zone and whose positions have been previously calibrated.

In order to guarantee the safe installation of the IR KM3NeT-EMSO equipment, regular maintenance of the autonomous reference acoustic beacons of the Long Base System is necessary.

This operation aims to maintain one of the 4 beacons: recovery by dropping the small anchoring line including the beacon, visual inspection and change of the beacon batteries, anchoring the line including the beacon, calibration of the new anchoring position of the acoustic beacon by acoustic interrogation using the RAMSES system during a circular course of the ship around the beacon.

Before dropping the beacon on the surface, a quality control of the acoustic positioning is carried out by interrogating the 4 reference beacons with the RAMSES system and comparing the position of the RAMSES transducer obtained by acoustic triangulation with that given by the GPS on board. A new check is carried out at the end of the mission after calibration of the new position of the beacon following its anchoring.

In order to ensure that the RAMSES system takes the acoustic velocity profile into account, a measurement of the velocity profile on the surface layer (0-100 m), which is subject to seasonal variations, is carried out in the area at the beginning of the mission.

This recurrent maintenance operation of the positioning beacons follows a first campaign carried out in December 2018, as well as a second performed in November 2019 with the ship Europe.

Mission 3 :

This operation should have followed a deep-sea campaign (planned in April 2020) whose purpose was to install the equipment built in the NUMerEnv project (BJS2, Benthic Robot, Radiometer, Bio-Camera and Seismometer). This campaign was postponed to 2022 due to a health crisis. In this context our objectives were revised downwards and the number of dives decreased (5 dives). The objectives of this leg are the following:
- Realize a measurement of the influence of the ROV lights on the KM3NeT/ORCA detector. A procedure detailing this operation has been written and provided to the operators of the equipment.
- Conduct a Survey of all the equipment already installed on the bottom and measure their precise immersion by reading the pressure sensor (Paro Scientific) of Ariane.
- Carry out a survey of the various cables laid on the seabed in order to verify their positions for future equipment deployments. A survey of three sections of the main cable is also planned as part of a seismic measurement on optical fiber (verification of the coupling between the cable and the bottom).
- Carry out a 3D mapping (mosaic) of the future intervention area of the benthic robot BathyBot.
- Take a sediment sampling within the framework of measurement on micro-plastics.
- Check the stability and make video monitoring of microorganisms at a depth of 400 metres.