An improved lidar method for monitoring surface waters: Experiments in the laboratory

Lidar monitoring of surface waters is usually applied to fluorescent substances like phytoplankton, yellow substances and oil. A lidar method is introduced which allows the measuring of the total attenuation coefficient at the laser wavelength considering also nonfluorescent substances besides fluorescent ones. Two signals are measured: first the total fluorescence lidar signal L, which is characterized by long path-lengths of the laser radiation in the water column, and second, the fluorescence F, which originates from the first layers immediately below the water surface. A simple experiment in the laboratory was performed using a nitrogen laser. Water samples containing algae and varying amounts of humic and ligninesulfonic acids were investigated. Synchronously the attenuation coefficients were measured. The F/L ratio yielded the total attenuation at the laser wavelength. Good correlations between the conventional and the lidar-derived attenuation coefficients were achieved described by squared correlation coefficients of R2 > 0.95. The F/L ratio seems to be a good tool in lidar monitoring of waters.