Tower-based radiometric observations at a coastal site in the Baltic Proper

An autonomous above-water radiometer was operated during the summer of 2005 on the Gustaf Dalen Lighthouse Tower (GDLT) off the Swedish coast in the Baltic Proper. Normalized water leaving radiances, L-WN(lambda), produced from measurements performed with the autonomous system at various center-wavelengths lambda in the 412-675 nm spectral range, were applied within the context of water quality monitoring and satellite ocean color validation activities. Specifically these in situ radiometric data were used to determine the chlorophyll a concentration through a regional band-ratio algorithm and to assess L-WN(lambda) derived from top-of-atmosphere Moderate Resolution Imaging Spectroradiometer (MODIS) observations. The in situ measurements collected during a bloom occurring in July 2005 were also used to investigate the spectral and small scale temporal-spatial variability of L-WN(lambda) in the presence of cyanobacteria.