TLS: tomoscopy by immersed laser spectroscopy

The underwater environment, especially in coastal areas, requires the use of a new generation of instrumentation to investigate the extreme spatial and temporal variability. As the undersea world is typically a scattering medium due to the presence of suspended matter, a high resolution tomoscopic system has been proved to be the most relevant means of investigation to get accurate spatiotemporal correlation of environmental parameters. In addition to the simple backscattering analysis, emphasis will be laid on the spectroscopic response of the medium in order to increase the discrimination power of the LIDAR. The work described focuses on the development of an underwater LIDAR platform, based on the use of a frequency doubled YAG Nd 3+ laser source and an optical receiver, using optical fibre technology coupled to a UV visible spectrometer. The versatile management of the LIDAR allows it to be operated according the most suitable configuration for short and medium range profiling. A maximum profile rate of one per second will be reached with 25 discrete spatial points. Each of them will represent a minimum of 1.35 m water layer depending on the time integration width. Completely sealed, the platform has been developed to be towed to provide 3D monitoring. First assessments have been carried out in a fifty meter long seawater tank, followed by sea trials in estuary conditions during a typically strong water column stratification period