Ocean Colour Instruments
Description
Ocean colour radiometers and imaging
spectrometers measure the radiance leaving
marine waters in the visible and near-IR
spectrum in the range 400–800 nm, where the
colour is characterised by the constituents
of the water – typically phytoplankton,
suspended particulate material and dissolved
compounds. Differences in the intensity of
light received in the different bands give
information on the concentration of a
variety of substances present in the ocean.
Radiance measurements may be affected by Sun
glint, since observations at subtropical
latitudes are contaminated by the bright
pattern of the specular reflection of the
Sun by the wavy sea surface.
Ocean colour instruments have very narrow
detection channels, around 10 nm wide, to
measure fine spectral details. The spatial
resolution of these instruments is typically
0.3-1 km. The more recent ocean colour
instruments have improved spatial, spectral
and radiometric resolution. The trend
towards multi-channel, multi-purpose
sensors, such as MODIS and MERIS, is
resulting in more instruments with an ‘ocean
colour’ capability. Most ocean colour
instruments have been flown on low-orbit
satellites. However, a new sensor (GOCI) was
launched in 2010 on a geostationary platform
(COMS), thus allowing the frequent
acquisition of data suitable for the
monitoring of rapid events, e.g. coastal
currents, algal blooms or floods – but with
limited coverage.
Significant calibration and validation
activities, together with algorithm
development for ocean colour instruments,
continues, particularly with respect to
measuring ocean productivity.
Applications
The colour of the oceans as seen from space
reveals phytoplankton pigment concentration
(chlorophyll), which is used as an indirect
measurement of ocean biomass and its
associated productivity. These parameters
are of considerable oceanographic and
climatological significance, since oceanic
productivity ‘drives’ the air-to-sea
exchange of biogenic greenhouse gases (e.g.
CO2).
Ocean colour imagery can also be used in
support of fisheries management or
protection, for example through
identification of biologically rich areas.
Other data that may be inferred from ocean
colour measurements include information
about suspended matter (useful in coastal
studies), biological productivity, marine
pollution and water dynamics (eddies,
currents, etc.) in coastal zones.
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Current & planned instruments
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Advanced GOCI
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Ocean Colour Spectrometer
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CZS
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OCM
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GOCI
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OCM (Oceansat-3/3A)
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MODIS
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OCS
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Multi-band UV/VIS Spectrometer
(ACE)
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OLCI
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MUS-SWIR
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SGLI
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MUS-UV/VIS/NIR
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VIIRS
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MODIS view of Mississippi river delta in
February 2008 showing flows of sediments and
nutrients.
GOCI example product.
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