Monitoring the Bio-optical State of the Baltic Sea Ecosystem with Remote Sensing and Autonomous In Situ Techniques - The Baltic Sea Basin - page 422

Fig. 20.7 A satellite Algal_1 (chlorophyll) image from MERIS in February 2008, overlaid with
Ferrybox chlorophyll- a fluorescence data. Operational web site www.ferrybox.no
The development of seasonal stratification may lead to large discrepancies
between chlorophyll -a derived from Ferrybox and from satellite data. It is there-
fore necessary to analyse Ferry Box data sets carefully. Some FerryBox lines are
also equipped with fluorometers that are sensitive to CDOM and/or fluorometers
that are sensitive to phycobilin pigments in order to detect cyanobacteria. Other
FerryBox lines, e.g. the FerryBox from Oslo to Kiel, also have radiance sensors on
deck to validate water-leaving radiance and remote-sensing reflectance derived from
satellite TOA measurements. In the Baltic Sea, there are several FerryBox systems
in operation (Ainsworth 2008 ) , which are summarized in Fig. 20.8 . The FerryBox
data will be used in future monitoring and forecasting of the marine environment,
e.g. within the EU FP7 project MyOcean.
20.2.2.2 The In Situ Autonomous NASA AERONET-Ocean Colour Stations
One way to improve truthing of satellite observations is to use autonomous
validation stations placed on fixed platforms, such as oceanographic towers or
light houses. This is done within the NASA AERONET-OC (AEROsol RObotic
NETwork - Ocean Colour), which is the most advanced examples of an autonomous
in situ station ( http://aeronet.gsfc.nasa.gov ). On an AERONET-OC tower, sun pho-
tometers are installed measuring atmospheric properties and water-leaving signals
(Zibordi et al. 2006 , 2009 ) . The in situ data provided is of very high value as the
oceanic and the atmospheric signal is measured simultaneously and continuously.
Currently, there are eleven AERONET-OC stations worldwide, three of which are
based in the Baltic Sea area: on Gustaf Dalén lighthouse at the Swedish coast in the