Submarine fluorescence lidar for environmental monitoring

    Stefan Harsdorf, Manfred Janssen, Rainer Reuter and Bernhard Wachowicz

    Carl von Ossietzky Universität Oldenburg
    Fachbereich Physik
    D-26111 Oldenburg, Germany

    email: {harsdorf / reuter} @las.physik.uni-oldenburg.de

    The German Bight is one of the world’s busiest ship-ping routes. Although a complex and comprehensive surveillance system has been installed by the littoral states, ship accidents cannot be completely precluded. Then chemical pollutants may come into the sea, either in containers or in free form. Fast and exact localisa-tion is an essential requirement for efficient recovery.
    Airborne fluorosensors are useful tools for the detec-tion of oil spills and other chemicals swimming on the sea surface. Due to the limited penetration depth of light into water, chemicals dispersed in the water col-umn or spread on the seafloor are mostly not detect-able.
    Therefore, a new fluorescence lidar has been devel-oped which will be operated as a payload of an ROV (remotely operated vehicle). The 3rd harmonic pulse of a Nd:YAG laser is applied as the light source of the instrument. Time- and wavelength-resolved signals are detected. Spatial scanning of the water column and the seafloor provides a small-scale localisation of optically active substances, and an analysis of the lidar spectra allows their classification.
    Additionally, a range gating video camera is integrated in the instrument to receive contrast enhanced images from the seafloor. The expanded second harmonic Nd:YAG laser pulse is used as the illumination source of the camera. These images support the interpretation of the lidar spectra. Furthermore, the ROV is equipped with auxiliary sensors for temperature, conductivity and depth (CTD) and a multispectra transmissometer. The system is specified for a maximum operation depth of 300 m.
    The submarine fluorescence lidar is an instrument which allows to remotely sense substances on the seafloor. It can also be applied for pipeline inspection and oceanographic measurements. Experiments in the laboratory have been carried out with success, and a prototype is in the realisation phase.