Shipborne laser remote sensing of the Venice lagoon

Abstract. A complex active remote sensing system has been used on board a small ship to extensively monitor the water quality of the Venice lagoon and nearby open sea. The system was composed of an UV lidar fluorosensor directly pointing to the sea surface and a laser fluorometer monitoring the water inside a cell continuously filled by a pump from a water depth of 1m. During the cruise, both apparata were collecting data in parallel. Laser-Induced Fluorescence (LIF) signals at selected wavelengths were acquired to monitor distributions of the different species. DOM and chlorophyll features were detected by the lidar fluorosensor upon excitation at lambda 355nm, while organic pollutants and oils were scanned in the fluorometer cell by laser emitting at lambda 266nm. In both cases, the accompanying water Raman signal was collected and used for normalizing spectral intensities. Absolute concentrations of different species were obtained off-line, when possible, by calibrating LIF intensities against analytical chemical findings on a number of water samples. Distributions of several substances, including industrial pollutants (oils and aromatic molecules), anthropogenic releases (yellow matter, suspended particles) and chlorophyll from phytoplankton were obtained along the ship route. A differential GPS instrument installed on board was used to georeference LIF data precisely, in order to produce thematic maps of the investigated areas.