Acoustic emitters in ARCA. Preparation of the M1-2026 sea operation

Tuesday 31 Mar 2026, 14:00 → 16:00 Europe/Zurich

AcousticData260331.odp

AcousticData260331.pdf

CANOPUS emitters as regular beacons

• Plan C to be able to constrain the ARCA absolute orientation.

• The use of this system will be rare: mostly silent and a few short (~ 24h) data taking periods

• The only urgency is to decide on the interrogation sequence.

• A documentation on the CANOPUS features (within what EXAIL is willing to disclose) is needed

Some information from Daniele:

• The CANOPUS transponder on JB8 should be turned ON and OFF on demand

• The programming of the transponder has been tried by Daniele

• The CANOPUS are responding to a specific interrogation code (with a minimum delay of 6s between two interrogations)

• The CANOPUS are all responsing with the same signal (features communicate to Daniele) mixing several frequencies on 16ms duration

Remarks/Conclusions:

• Proposal for a sequence of 150s to save battery lifes (3 years according to EXAIL) and allow for future survey and boxin is accepted (all ?)

• 16 ms long + mixture of frequencies may give a better time resolution compared to our regular LBL beacon, but other inputs are needed: frequencies used, response of our piezos to them. (Miquel)

Action items:

• Propose an emitting sequence - Described in an auxiliary document (Lilian)

• Make a WF from the signal features and load into the KM3NeT db (?)

Two new CANOPUS+LBL tripods

• The plan A to constrain the ARCA absolute orientation

• An ensemble of 4 working LBL+Canopus tripods is mandatory.

Remarks/Conclusions:

• The locations of all the TABs were already a consensus combining the geometry, the visibility, the bathymetry (Lilian)

• The proposal is to immediately replace TAB2 and TAB3 by deploying two new tripods in their vicinity (Lilian)

• Several baselines involving TAB2 and TAB3 were used by EXAIL to improve the box-in positions suggesting that nothing is screening their LBL (Valentin)

• A problem restricted to the LBL is probably the cause of their silence. Other causes are not excluded such as a fallen tripod, a battery of a cable problem. Moving the tripod closer to the BB will probably not help much (Miquel)

• Moving TAB2 and TAB3 is not garanteed to (partly ?) reveal the LBL signals and time consuming (all)

Actions items:

• Check that this part can be done early during the sea operation when ARCA acoustic stream is available (Daniele)

• Provide a deployment document and deployment scheme for the sea operation (Daniele)

• Provide to the non-experts a no-brainer script/piece of software to analyse the acoustic data online for the touchdown test (Valentin and calibration group)

Relative depth measurements

• Plan B to be able to constrain the ARCA absolute orientation

• Rely on the sensitivity of a ROV pressure sensor to obtain accurate relative depths.

Remarks/Conclusions:

• The depth of the existing emitters TAB1, TAB6, MH, JB3 and JB4 must be measured (all)

• The upcoming emitters MUST also be measured (Maarten)

• The measurement is relatively short, the moment and the order must be optimized (Daniele)

• A resolution around 10cm can be obtained with a paroscientific sensor (www.paroscientific.com) equiped with a crystal (Vincent)

• By experience, it is easier and more accurate to have the ROV landed on the seabed near by the object rather than grabbing it (Vincent)

• Up to date drawings and dimensions of the mechanical structures holding the emitter is hard to find (Maarten)

Action items:

• Check that the emitters (JB3 and JB4)in the BB can be accessed (Daniele)

• Check the pressure sensor type/model foreseen in the upcoming sea operation (Daniele)

• Collect the latest drawings of ARCA elements such as the junction boxes - Update the input_tables document accordingly (Lilian)

Settings for the new emitters

• Define necessary waveforms for the upcoming LBL emitters (two on TABs and probably 4 on strings)

• No urgency since the beacon programming is usually done while at Malta

Remarks/Conclusions:

• Recycling WFs already assigned to emitters (even assumed dead) on the seabed should be avoided (Maarten)

Action items:

• Open a Git issue and initiate the discussion (Lilian)

• Verify the list of new strings equiped with a beacon (Daniele, Lilian)

1 Settings of the JB8 Canopus emitter

Determine the rate at which the Canopus emitter on JB8 is waked up to activate a communication from the other Canopus beacons.

2 Possible/Optimal positions of TAB2/TAB3 or their substitutes

Determine the positions of the silent LBL emitters if they are finally emitting signals. Identify additional locations for their substitutes if it turns out that the visibility of the initial positions is not favorable.

3 Measurement of the relative depth of some existing emitters

Discuss the procedure (how, what, when) to measure the relative depth of the working emitters already on the field.

4 Settings of the new LBL emitters

Discuss the list and the settings of the new emitters that will be deployed during the sea operation. It includes the new TAB and possibly some on-anchor or on-JB beacons.