Chapter 7: APPLICATIONS
Higher spectral resolution potentially leads to more informative remote
sensing systems. The so-called hyperspectral remote sensing involves
systems with very fine spectral resolution and many wavelengths.
Hyperspectral remote sensing is expected to improve the interpretation of the
complex biophysical processes controlling optical properties of the coastal
ocean.
Remote sensing of ocean color is a passive method, since the sun is the
source of light. The photons from the sun follow different pathways before
reaching the remote sensor. The light entering the sensor originates from
scattering of photons by the atmosphere, reflection of direct sunlight from
the sea surface (specular reflection), and the upwelling light that is backscattered from below the sea surface (Figure 7-6).
The upwelling light scattered from below the sea surface carries useful
information in relation to the water body properties. This light is, however,
attenuated on its pathway from the sea surface to the remote sensor because
of absorption and scattering by the atmosphere.
The specular reflection at the sea surface and atmospheric attenuation
represent noise for remote sensing of ocean water properties using color.
Specular reflection from the sun can be avoided by changing the orientation
of the detector with respect to the position of the sun. This, nevertheless,
does not help in eliminating the flux scattered from the atmosphere that
reaches the sensor at many angles. More than 80% of the light reaching
satellite sensors may be of atmospheric origin (Morel, 1980). Techniques for
atmospheric correction are therefore an essential component of remote
sensing of the ocean color (Gordon, 1997).
Figure 7-6 illustrates the main factors that influence upwelling light backscattered from below the sea surface. (This diagram is a bit simplified,
because it does not show multiple reflections and scattering.) Direct and
scattered (diffuse) solar radiation penetrating the sea surface is absorbed and
scattered by the water molecules and suspended and dissolved materials
contained in the near-surface water. In coastal areas, sunlight may reflect
from the ocean bottom.
Ocean color imagery represents properties of a thicker layer than the
microwave and infrared imagery. The color is therefore a more conservative
characteristic of the water mass than the surface roughness or SST, and it
better defines dynamical ocean features. These features are often well clearly
seen in the chlorophyll-D band (Yentisch, 1984), though, strictly speaking,
phytoplankton is not a conservative tracer. In coastal regions, other color
imagery products such as the yellow substance and suspended sediment may
be even better tracers than chlorophyll (Kopelevich et al., 1998).
The intrinsic color of the ocean is defined by spectral variations in
reflectance R s which according to IOCCG (2000) is defined as follows:
449
Higher spectral resolution potentially leads to more informative remote
sensing systems. The so-called hyperspectral remote sensing involves
systems with very fine spectral resolution and many wavelengths.
Hyperspectral remote sensing is expected to improve the interpretation of the
complex biophysical processes controlling optical properties of the coastal
ocean.
Remote sensing of ocean color is a passive method, since the sun is the
source of light. The photons from the sun follow different pathways before
reaching the remote sensor. The light entering the sensor originates from
scattering of photons by the atmosphere, reflection of direct sunlight from
the sea surface (specular reflection), and the upwelling light that is backscattered from below the sea surface (Figure 7-6).
The upwelling light scattered from below the sea surface carries useful
information in relation to the water body properties. This light is, however,
attenuated on its pathway from the sea surface to the remote sensor because
of absorption and scattering by the atmosphere.
The specular reflection at the sea surface and atmospheric attenuation
represent noise for remote sensing of ocean water properties using color.
Specular reflection from the sun can be avoided by changing the orientation
of the detector with respect to the position of the sun. This, nevertheless,
does not help in eliminating the flux scattered from the atmosphere that
reaches the sensor at many angles. More than 80% of the light reaching
satellite sensors may be of atmospheric origin (Morel, 1980). Techniques for
atmospheric correction are therefore an essential component of remote
sensing of the ocean color (Gordon, 1997).
Figure 7-6 illustrates the main factors that influence upwelling light backscattered from below the sea surface. (This diagram is a bit simplified,
because it does not show multiple reflections and scattering.) Direct and
scattered (diffuse) solar radiation penetrating the sea surface is absorbed and
scattered by the water molecules and suspended and dissolved materials
contained in the near-surface water. In coastal areas, sunlight may reflect
from the ocean bottom.
Ocean color imagery represents properties of a thicker layer than the
microwave and infrared imagery. The color is therefore a more conservative
characteristic of the water mass than the surface roughness or SST, and it
better defines dynamical ocean features. These features are often well clearly
seen in the chlorophyll-D band (Yentisch, 1984), though, strictly speaking,
phytoplankton is not a conservative tracer. In coastal regions, other color
imagery products such as the yellow substance and suspended sediment may
be even better tracers than chlorophyll (Kopelevich et al., 1998).
The intrinsic color of the ocean is defined by spectral variations in
reflectance R s which according to IOCCG (2000) is defined as follows:
449