Depth resolved detection of oceanographic variables in the St. Lawrence estuary using a laser fluorosensor: instrument characteristics and first results†

Abstract

A 64-channel Laser Environmental Airborne Fluorosensor (LEA F) system for sea surface oil detection was modified for continuous depth-resolved detection of gelbstolT and chlorophyll a spectral fluorescence, and water Raman scattering. The system was successfully tested during shipborne and airborne experiments in the SI. Lawrence Estuary. System performance was studied, and the best integration time to optimize the signal to noise ratio (SIN) was determined using dilTerent statistical procedures such as the geophysical and robust statistical methods. In general, raw data indicated SIN of about 150, 10, and 4 for Raman. gelbstolT and chlorophyll a signals, respectively. Results with calibrated LEAF spectra clearly indicated that, with this system, water Raman scattering, geibstolT and chlorophyll a signals could be detected down to a maximum depth of 4·8 m. Spatial distribution of these quantities compared well with simultaneously observed ill Silll structure of oceanographic variables, such as, underwater light attenuation, salinity and chlorophyll a fluorescence. In the perspective of modelling primary production in coastal and estuarine waters in the SI. Lawrence system (Case II waters), the utilization of LEAF should provide an adequate representation of the spatial and temporal variation pattern of oceanographic variables, at scales between those from ships and satellites.