Hydrographic LIDAR in space:
    Fermats Principle as an analytical approach for
    atmospheric radiative transfer simulation.

    R. Reuter, O.Zielinski

    Carl von Ossietzky University of Oldenburg
    Physics Department, D-26111 Oldenburg, Germany

    r.reuter@las.physik.uni-oldenburg.de
    o.zielinski@las.physik.uni-oldenburg.de

    Active remote sensing with laser flurosensors enables the investigation of various oceanic parameters, such as dissolved organic matter (gelbstoff) or chlorophyll. Long-term surveillance of the North Sea with a laser fluorosensor mounted on a DO 228-212 aircraft, at a flight altitude of 300m, have shown the capability of two-dimensional mapping of coastal zones like the German Bight.
    Recently, the feasibility of measuring water-column parameters with fluorescence lidar at flight altitudes higher than 300 m has met increasing interest. The feasibility of such measurements using platforms at altitudes of up to 800 km are studied, which would allow to operate the instrument as an attachment to atmospheric lidars.
    A cloudless and stratified atmosphere with various aerosol and ozone conditions is taken into consideration. Particular emphasis is put onto the radiative transfer of the atmosphere at wavelengths which are relevant to hydrographic fluorescence measurements.
    A simulation is presented, using Fermat's principle as an analytical approach to describe the radiative transfer processes for a horizontally stratified atmosphere. A number of results are presented concerning the geometrical aspects of radiative transfer through the atmosphere, such as optimised lidar parameters and effects of turbulence and dispersion.
    It is outlined that data simultaneously measured with an atmospheric lidar (e.g. LITE) allows to correct the fluorescence signal for atmospheric effects, yielding quantitative results of fluorescent matter concentrations in the sea.