Altus

Ifremer

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Altus

ALTUS, a precision ultrasound altimeter to register the variations of sediment levels :

Evaluating precisely the deposition / erosion of sediments constitutes a major input data to assess the sedimentary balances in coastal areas.

These evaluations aim to :

	state and quantify a particulate deposition during slack waters both in estuarine and bay environments,
	evaluate the sediment erosion due to hydrodynamics,
	monitor the altimetric evolution of a mud flat or of a sandy tidal zone over several months.

For all theses purposes, this evaluation represents a worthy tool to validate digital models describing the sedimentary transport.

The ALTUS system was designed to meet such expectations.

Principle of the device :

This device works according to the echo sounder principle, but with a different frequency of ultrasound emission (2 MHz) ; the apparatus includes a module providing energy, electronics and sensor pressure and designed to be buried within the sediment, as well as
a transducer placed on a support.

The Altus System

Main characteristics 

2 measurement scales : 20 to 70 cm (accuracy : ± 2 mm)
20 to 200 cm (accuracy : ± 5 mm)

	Resolution : 0.6 mm in both cases
	Recording of the water head (up to 20 m) and of 1 to 4 detection thresholds of the sediment levels (programmed in the laboratory after calibration with the target sediment). These levels outline the " sedimentation state " of the disposed material.
	The memory capacity approaches 3 months and the energy capacity 2 to 4 years in order to allow a sampling frequency of 1 sample per 15 mn. According to the targets, which might be short term or long term (over several months) ones, the shot frequency can be scheduled to meet the memory capacity of the apparatus.

Some examples

Field implementations...

A mud flat area : the "Vasière de Brouage" (Marennes-Oléron, on the French Atlantic coast)

...and data valuations : the Seine estuary

This system is an emanation of the collaboration between Ifremer's Brest center and the Micrel Company (Hennebont, Brittany, France) ; it was developed within the frame of the European Mast 3 "INTRMUD" program, which ended in 1999.

Contact :

Philippe.Bassoullet@ifremer.fr
Herve.Jestin@ifremer.fr