First results after the deployment of a subsea geodetic monitoring system

<p>Geodetic networks at sea are necessary to monitor active faults and the long term displacement of tectonic plates. iXblue has developed a new integrated subsea monitoring system: Canopus</p><p>The Canopus transponders are enable to regularly measure precisely the distance between the transponders that are in acoustic line of sight. The measurement are stored in a memory inside each beacon and can be collected from surface using acoustic modem. In collaboration with the IUEM, and in the framework of ERC Focus project, 8 Canopus beacons were deployed at each side of the North Alfeo Fault in Sicilia for a  4 years monitoring program. To prepare the deployment, a first experiment took place in Brest Bay in July 2019, and a second one in La Ciotat Bay in September 2020. Thanks to Delph subsea positioning software, simulations enable to confirm acoustic line of sight between beacons considering the local bathymetry, the sound velocity profile and the height of the transponders above the seabed. The final deployment took place in October 2020.  We present here the series of test and  simulations conducted before the final deployment and the first results after deployment.</p>

Performance Analysis of Target Depth Classification Algorithm Based on Sea Experiment Data

Cross-spectrum signals can be calculated by the pressure signals. The sign distribution of cross-spectrum active component can be effectively used for target depth classification algorithm. The algorithm is applicable for depth classification of targets where frequencies can only excite the first two normal modes. The corresponding research results are mainly based on the theoretical study. There are few researches on the algorithm performance based on experiment results. To overcome this research lack, based on the effective depth model, the effects on various receiving depth, source frequency, and received signal-to-noise ratio on the algorithm performance have been studied in this paper. The influence of sound velocity profile parameters (negative gradient, thermocline intensity, thermocline thickness, and up-boundary depth) on the algorithm performance has also been researched. According to the simulation results, proper adjustment of the receiving depths can effectively improve the algorithm performance. The source frequency primarily affects the position of the ideal receiving depth which can be appropriately adjusted according to the depth classification requirements of the real sea environment. The algorithm performance improves gradually with the increase of signal-to-noise ratio. Moreover, the algorithm can also be applied under the conditions of negative gradient and thermocline. The comprehensive sound velocity profile parameters have a large impact on the depth classification performance of the algorithm. Even in the case of strong negative gradient or strong thermocline, the robustness of the algorithm is still high. The feasibility of our presented method has been verified by sea experiment. The practical application value of the ideal receiving depth has been researched and validated. The factors affecting the algorithm performance including line spectrum continuity and received signal-to-noise ratio have also been analyzed in our simulation and real sea experiments.

The Weakest Point Evaluation Method for the Control Range of the Sound Velocity Profile Station

Sound velocity measurement is an important part of multi-beam sounding, and its accuracy directly affects the coordinate reduction of sounding points. Because of the variability of seawater sound velocity in time and space, the layout density of acoustic section stations directly affects the accuracy of multi-beam sounding. Over-dense layout wastes resources and causes inefficiency; over-sparse layout is not accurate enough to control the entire survey area. Based on the constant gradient acoustic ray tracing algorithm, this paper constructs the accuracy evaluation model of the weakest water depth point of acoustic profile station control, and analyses whether the existing multi-beam acoustic profile station layout scheme can satisfy the accuracy requirements of multi-beam sounding through an example calculation, which provides a theoretical basis for adjusting the layout scheme of acoustic profile station for field surveyors.