Ancillary instruments

The acquisition of scientific data is supported by various pieces of equipment which facilitate the measurement and deployment of mobile equipment, or contribute to improving the quality of such data.

Ships operating multiple sound acquisition systems (multibeam echo sounders, current profilers, sub-bottom profilers, etc.) are fitted with an OSEA synchronization unit to prevent interference between acoustic emissions.

All the ships undertaking bathymetry carry a bathythermograph for the purpose of profiling the velocity of the water column, an essential task to ensure the precision of data generated by the echo sounders. On most of the ships the validity over time of the bathythermograph data is monitored using a hull-fitted sound velocity sensor.

In addition to the equipment mentioned above, there are tools for deploying mobile equipment. The ships Pourquoi pas ?, Atalante and Thalassa feature Travocean tubes of various diameters which enable operators on the working deck to install and submerge instruments under the ship’s keel.

	Synchronization of acoustic	Bathythermograph	Hull-fitted sound velocity sensor	Travocean Tubes
Marion Dufresne	K-SYNC (Kongsberg)	Sippican Mk21	MiniSVS	1 TVO
Pourquoi pas ?	OSEA	Sippican Mk21	Reson SVP-C	1 TVO 800 2 TVO 500
L’Atalante	OSEA	Sippican Mk21	MiniSVS	1 TVO 800
Thalassa	OSEA	Sippican Mk21	MiniSVS	1 TVO 300 1 TVO 500
Antea	OSEA	Sippican Mk21
Alis	OSEA	Sippican Mk21
L’Europe	OSEA	Sippican Mk21	MiniSVS
Thalia		Sippican Mk21	MiniSVS
Haliotis			MiniSVS

Synchronization of acoustic equipment

The acoustic synchronization system OSEA manages acoustic equipment to prevent any interference between sound emissions. The system can function autonomously (principal) or be piloted by a “master” acoustic system. Slave equipment thus depends on signals coming from the master.

The unit can be configured using special software developed by IFREMER.

Bathythermograph

A sensor capable of making acoustic measurements using the echo principle (difference between the emission and reception of the acoustic wave) is essential for determining accurately the speed of propagation, or velocity, of the sound wave in water.

To this end, the ships of the fleet are fitted with a Sippican Mk21 data acquisition system which profiles this velocity throughout the water column via eXpendable BathyThermograph probes launched from the ship.

An XBT probe is a small projectile with a lead tip and a plastic shell containing a coil of fine copper wire.

This probe is inserted into a handheld launcher which fires it into the sea.

As the probe sinks into the water column, the wire coil unwinds and transmits the measurements made by a thermistor to a PC-type microcomputer fitted with a MK 12 card.

The program installed on the PC enables the operator to monitor the T=f(P) measurement in real time, and record the curve which will then be injected into the acoustic instruments after formatting by the Doris program.

Hull-fitted sound velocity sensor

The oceans are permanently moving bodies of water and their physical characteristics vary according to where the study takes place, the time of year, the time of day, weather conditions and so on.
So the validity of each velocity profile measured by the bathythermograph is of limited duration. In order to verify this validity in real time, all the ships have a sound velocity sensor fitted to their hull (except for the Alis and the Antea).
This velocity sensor measures continuously the propagation speed of sound in the subsurface of the sea and compares the results to the surface data obtained by the bathythermograph.

When the difference exceeds a certain threshold, it emits an alarm and a new sound-velocity profile is made using the bathythermograph.

Valeport MiniSVS

The MiniSVS is a Doppler-effect sound velocity sensor which functions at a frequency of 2.5 MHz. It is mounted in a stainless-steel canister which features an automatic bleeding valve and is supplied by an independent centrifugal pump. This sound velocity sensor is fitted to the Atlante.

Measuring range: 1375–1900 m/s
Resolution: 0.001 m/s
Accuracy (maximum theoretical error): approx. 0.017 m/s

Reson SVP-C

The Reson SVP-C is the Doppler-effect sound velocity sensor fitted to the Pourquoi. It is mounted in a stainless-steel canister which features an automatic bleeding valve and is supplied by an independent centrifugal pump.

Measuring range: 1350–1800 m/s
Resolution: 0.01 m/s
Accuracy: approx. 0.05 m/s

Travocean Tubes

Travocean tubes enable operators on the working deck to position mobile instruments under the ship. These tubes cross the various decks down to the keel. A composite mounting receives the instruments to be deployed under the ship. The mounting is maintained in position thanks to an air chamber inflated with compressed air.

The 800 mm diameter tubes (Pourquoi pas ?, Atalante) are indexed, the orientation of their lower section in relation to the fore-and-aft line of the ship always being identical.