Geoscience Reference
In-Depth Information
Chapter 20
Monitoring the Bio-optical State of the Baltic
Sea Ecosystem with Remote Sensing and
Autonomous In Situ Techniques
Susanne Kratzer, Kerstin Ebert, and Kai Sørensen
Abstract
This chapter focuses on recent advances in water quality monitoring of
the Baltic Sea using remote sensing techniques in combination with optical in situ
measurements. Here the Baltic Sea ecosystem is observed through its bio-optical
properties, which are defined by the concentration of optical in-water constituents
governing the spectral attenuation of light. In the introduction, typical geograph-
ical patterns and seasonal variations of optical properties and the cause of the
mass occurrence of cyanobacterial blooms in summer are discussed. The optical
characteristic of Baltic Sea waters is clearly dominated by a relatively high load
of dissolved organic matter and, during the productive season, by phytoplankton
growth, stimulated by nutrients mostly originating from land. In the coastal zone,
inorganic suspended matter also has a significant effect on the light attenuation,
which increases with proximity to land. The ecological status of the coastal zone
may be synthesized using a bio-optical model, summarizing important ecosys-
tem state variables such as terrestrial runoff and phytoplankton production. The
optical properties can also be observed with visible, spectral satellite remote sens-
ing providing repetitive and optically consistent data for the whole Baltic Sea
basin. Such observations have already significantly influenced our understand-
ing of Baltic Sea dynamics and provide us with a new look into this brackish
ecosystem. The focus in this chapter is on the ocean colour sensor 'Medium
Resolution Imaging Spectrometer' (MERIS), which since 2002 is flying continu-
ously onboard the European Environmental Satellite ENVISAT, developed by the
European Space Agency (ESA). The advantage of MERIS data is its good spa-
tial resolution of 300 m allowing the analysis of coastal features and bays of the
Baltic Sea. Algorithms to retrieve bio-optical parameters from MERIS data are
continuously improved and extended. The MERIS mission will be continued with
the Ocean and Land Colour Instrument (OLCI), an optically similar sensor which
will be flown on SENTINEL-3, scheduled to be operational until 2023, to assure
