Geoscience Reference
In-Depth Information
measurements, ship-based data may provide complex bio-geochemical parameters
including the information on vertical distribution. Horizontal transects from ships-
of-opportunity provide improved temporal and spatial resolution using automatic
measurements.
20.2 Methods Applied
20.2.1 Remote Sensing Methods
20.2.1.1 Background
In order to monitor an aquatic ecosystem, various biological, chemical, and phys-
ical parameters, indicating its state, are required. Marine satellite remote sensing
uses a wide range of measurement techniques to derive a set of important bio-
geophysical parameters. The satellite sensors work in active or passive mode. The
parts of the electromagnetic spectrum used are in the microwave, infrared, and
visible/near-infrared range. Active microwave sensors, i.e. radars, are applied to
derive information on sea surface height, wave height, wind surface fields, and the
microwave radiometry is used to detect sea-ice zones and ice parameters, temper-
detect surface accumulations of cyanobacteria in the Baltic Sea (Subramaniam et al.
the end of 2009, is another passive microwave radiometer, which will be used to
derive ocean salinity.
20.2.1.2 Ocean Colour Remote Sensing
In this chapter the focus lies on ocean colour remote sensing, i.e. remote sensing
in the visible-near-infrared (VIS/NIR) range, 400-900 nm, with passive satellite
radiometers. VIS/NIR radiation, i.e. the sun light, is scattered and absorbed on its
way through the atmosphere. As the radiant flux reaches the sea surface, some of
it is reflected, and some of it is refracted as it enters the water body. Once in the
water, the radiant flux is either absorbed or scattered by the optical components
in the water body, which changes its spectral signature. The radiance that is scat-
tered back into the atmosphere, the so-called water-leaving radiance, now contains
information about the optical water constituents. It is changed, again, on its way
through the atmosphere. The VIS/NIR signal measured remotely by a sensor placed
on an aircraft or a satellite therefore carries information on both the optical in-water
constituents and the atmosphere. The NIR channels of the radiometer are used for
atmospheric correction, whereas the visible channels are used to derive information
about water quality.