Caractérisation du sédiment de surface par sondeur acoustique S-ALTUS - Etude des potentialités du S-ALTUS

Beyond the simple measurement of the altimetry, the recording of the whole signal of the echoes measured by the autonomous sounder S-ALTUS may lead to extra information about the superficial sediment. This study wants to assess the potency of the SALTUS to identify the nature of the bottom sediment and also to detect a superficial layer using the shape of the signal. An accurate measurement of the technical attributes of the S-ALTUS was carried out in an acoustic pool. Then, few tests were made on different thickness of a first sediment layer set on an other sediment base (fine sand on coarse sand, soft mud on sand, soft mud on hard mud, sand on hard mud, etc..). A cross-correlation between the emitted signal and the backscattered echo sometimes allows detecting two successive echoes and then measuring a layer thickness in particular in the case of soft mud on hard mud or sand. The echoes backscattered from different types of sediment were also recorded and compared in order to determinate relevant criteria (energy, length of the signal, rising front,…) which would help to differentiate them from one another. In spite of the high variability of the echoes, a Principal Components Analysis (PCA) allowed to differentiate sand from mud in two cases out of three. However, this algorithm needs to be validated using more data. Even though no simple and decisive results were found during this study, it is interesting to become aware of the complexity of the considered issue which surely needs to be continued.