20 Ocean-Colour Radiometry
351
Given all these technological breakthroughs, especially in the last decade, we
might ask: What are the additional developments that might be realised in the near
future? If we compare what might be on the wish list of scientists against the impressive list of what has been already realised, it might be speculated that the next
technological breakthroughs would come from sensors designed to yield nanometre,
or sub-nanometre spectral resolution at least in selected wavebands. Such sensors
would allow development and use of algorithms that exploit either small variations in the spectral form of reflectance, or that examine filling of Fraunhofer lines
through trans-spectral processes, both to improve atmospheric correction and interpretation of water-leaving radiances (note: Fraunnhofer lines, the dark features in the
solar spectrum, may get filled to smaller or greater extent in the water-leaving radiance, depending on the trans-spectral processes in the ocean, such as fluorescence
or Raman scattering, which is commonly referred to as Fraunhofer line filling).
Other technological innovations might come from success in combining features
in satellite sensors that are at present mutually exclusive: such as bringing together
high spatial resolution with high repeat frequency and global coverage. Perhaps
such goals would be realised through constellations of satellites, which would also
facilitate minimising loss of coverage due to clouds.
The CZCS was launched as a proof-of-concept mission. All the subsequent
ocean-colour satellites have been improvements over the CZCS, with technical specifications that differed from those of the CZCS, and from each other, such that each
of them has been pioneers in their own right. Whereas these innovations have promoted new interpretations and applications of ocean-colour data, it has also made it
difficult to merge of data from different satellites (IOCCG, 2007). In the climate context, it is essential to create the longest possible time series of ocean-colour data in
a seamless and continuous fashion. It is to be hoped that, in the future ocean-colour
missions, the need for continuity would not be forgotten in the urge to innovation
and creativity.
20.3 New Products
The brief overview of the advances in recent years clearly demonstrates that the
technology has been able to respond in a very effective manner to our improved
appreciation of the potential of ocean-colour sensors, over and above what had
been conceived of in the initial years of development of the field. But arguably,
the interpretation of data from the improved sensors has not yet reached its full
potential.
The atmospheric signal, and not the ocean signal, remains always the dominant signal at the level of the satellite, such that it is atmospheric correction, and
not radiometric accuracy at the level of the satellite, that will always determine
the inherent precision of derived radiometric quantities at the sea level. In spite of
the tremendous progress already made in atmospheric correction of ocean-colour
data (Gordon, Chapter 17, this volume), it remains one of the major hurdles in the
use of ocean-colour data in the sense that the accuracy and precision of retrieved
351
Given all these technological breakthroughs, especially in the last decade, we
might ask: What are the additional developments that might be realised in the near
future? If we compare what might be on the wish list of scientists against the impressive list of what has been already realised, it might be speculated that the next
technological breakthroughs would come from sensors designed to yield nanometre,
or sub-nanometre spectral resolution at least in selected wavebands. Such sensors
would allow development and use of algorithms that exploit either small variations in the spectral form of reflectance, or that examine filling of Fraunhofer lines
through trans-spectral processes, both to improve atmospheric correction and interpretation of water-leaving radiances (note: Fraunnhofer lines, the dark features in the
solar spectrum, may get filled to smaller or greater extent in the water-leaving radiance, depending on the trans-spectral processes in the ocean, such as fluorescence
or Raman scattering, which is commonly referred to as Fraunhofer line filling).
Other technological innovations might come from success in combining features
in satellite sensors that are at present mutually exclusive: such as bringing together
high spatial resolution with high repeat frequency and global coverage. Perhaps
such goals would be realised through constellations of satellites, which would also
facilitate minimising loss of coverage due to clouds.
The CZCS was launched as a proof-of-concept mission. All the subsequent
ocean-colour satellites have been improvements over the CZCS, with technical specifications that differed from those of the CZCS, and from each other, such that each
of them has been pioneers in their own right. Whereas these innovations have promoted new interpretations and applications of ocean-colour data, it has also made it
difficult to merge of data from different satellites (IOCCG, 2007). In the climate context, it is essential to create the longest possible time series of ocean-colour data in
a seamless and continuous fashion. It is to be hoped that, in the future ocean-colour
missions, the need for continuity would not be forgotten in the urge to innovation
and creativity.
20.3 New Products
The brief overview of the advances in recent years clearly demonstrates that the
technology has been able to respond in a very effective manner to our improved
appreciation of the potential of ocean-colour sensors, over and above what had
been conceived of in the initial years of development of the field. But arguably,
the interpretation of data from the improved sensors has not yet reached its full
potential.
The atmospheric signal, and not the ocean signal, remains always the dominant signal at the level of the satellite, such that it is atmospheric correction, and
not radiometric accuracy at the level of the satellite, that will always determine
the inherent precision of derived radiometric quantities at the sea level. In spite of
the tremendous progress already made in atmospheric correction of ocean-colour
data (Gordon, Chapter 17, this volume), it remains one of the major hurdles in the
use of ocean-colour data in the sense that the accuracy and precision of retrieved