FROM CELLS TO THE OCEAN: SATELLITE OCEAN COLOR
M. R. Lewis l and J. J. Cullen 2 . 3
IDepartment of Oceanography
Dalhousie University
Halifax, Nova Scotia
Canada B3H 4J 1
2Bigelow Laboratory
West Boothbay Harbor, Maine
USA
ABSTRACT
Variations in the color of the ocean as seen from space are principally due to variations in the concentration and
optical properties of biogenic materials, dissolved and particulate, in the upper ocean. From 1978 to 1986 the
NIMBUS-7 Coastal Zone Color Scanner observed these variations over the global ocean; the wealth of data that
has resulted is just now being appreciated. The resultant ability to observe the ocean from a biological perspective
over synoptic scales revolutionized the field.
The satellite observations require algorithms to interpret the received signal in terms of meaningful geophysical
quantities or processes. Most of the signal results from the atmosphere and corrections to permit analysis of the
ocean signal is non-trivial. Assuming that this can be done with acceptable accuracy, it is still necessary to relate
the observations of radiance leaving the surface of the ocean to more useful variables such as the concentration
of chlorophyll in the sea surface or the primary productivity of the ocean. The link between the observations and
the desired retrieval are the so-called bio-optical algorithms.
The relationship between water-leaving radiance and chlorophyll in the water column is not simple because
most of the chlorophyll is contained within phytoplankton particles of varying dimension and with varying internal
concentration of chlorophyll. The presence of ancillary and detrital pigments, in addition to chlorophyll, and the
presence of non-chlorophyllous particles further complicate the issue. Two approaches to the bio-optical
algorithms have been taken to resolve these problems. The first attempts to describe empirically the variability
in particle size and composition in terms of coefficients of statistical relationships between water-leaving radiance
and chlorophyll concentration. Primary production is described in a similar fashion. The second, not mutually
exclusive, relies on first principles of radiative transfer and the physiology of phytoplankton coupled with a
detailed understanding of the nature and size distribution of the particle popUlation and their optical properties.
One of the challenges of the latter path is to reproduce the water-leaving signal given the solar input and detailed
knowledge of the particle population from analysis of individual cells. The inverse problem, infering the
individual cell characteristics from the water-leaving radiance signal, is equally or more challenging.
Here, the bases for the remote measurement of ocean color from space, and the algorithms used in the
estimation of chlorophyll concentration and primary productivity from these remote measurements will be
discussed with a view towards interpretation based on the characteristics of the ensemble of individual particles
in the upper ocean.
3Present Address: Department of Oceanography
Dalhousie University
Halifax, Nova Scotia
Canada B3H 411
NATO AS! Series, Vol. G 27
Particle Analysis in Oceanography
Edited by S. Demers
© Springer-Verlag Berlin Heidelberg 1991
M. R. Lewis l and J. J. Cullen 2 . 3
IDepartment of Oceanography
Dalhousie University
Halifax, Nova Scotia
Canada B3H 4J 1
2Bigelow Laboratory
West Boothbay Harbor, Maine
USA
ABSTRACT
Variations in the color of the ocean as seen from space are principally due to variations in the concentration and
optical properties of biogenic materials, dissolved and particulate, in the upper ocean. From 1978 to 1986 the
NIMBUS-7 Coastal Zone Color Scanner observed these variations over the global ocean; the wealth of data that
has resulted is just now being appreciated. The resultant ability to observe the ocean from a biological perspective
over synoptic scales revolutionized the field.
The satellite observations require algorithms to interpret the received signal in terms of meaningful geophysical
quantities or processes. Most of the signal results from the atmosphere and corrections to permit analysis of the
ocean signal is non-trivial. Assuming that this can be done with acceptable accuracy, it is still necessary to relate
the observations of radiance leaving the surface of the ocean to more useful variables such as the concentration
of chlorophyll in the sea surface or the primary productivity of the ocean. The link between the observations and
the desired retrieval are the so-called bio-optical algorithms.
The relationship between water-leaving radiance and chlorophyll in the water column is not simple because
most of the chlorophyll is contained within phytoplankton particles of varying dimension and with varying internal
concentration of chlorophyll. The presence of ancillary and detrital pigments, in addition to chlorophyll, and the
presence of non-chlorophyllous particles further complicate the issue. Two approaches to the bio-optical
algorithms have been taken to resolve these problems. The first attempts to describe empirically the variability
in particle size and composition in terms of coefficients of statistical relationships between water-leaving radiance
and chlorophyll concentration. Primary production is described in a similar fashion. The second, not mutually
exclusive, relies on first principles of radiative transfer and the physiology of phytoplankton coupled with a
detailed understanding of the nature and size distribution of the particle popUlation and their optical properties.
One of the challenges of the latter path is to reproduce the water-leaving signal given the solar input and detailed
knowledge of the particle population from analysis of individual cells. The inverse problem, infering the
individual cell characteristics from the water-leaving radiance signal, is equally or more challenging.
Here, the bases for the remote measurement of ocean color from space, and the algorithms used in the
estimation of chlorophyll concentration and primary productivity from these remote measurements will be
discussed with a view towards interpretation based on the characteristics of the ensemble of individual particles
in the upper ocean.
3Present Address: Department of Oceanography
Dalhousie University
Halifax, Nova Scotia
Canada B3H 411
NATO AS! Series, Vol. G 27
Particle Analysis in Oceanography
Edited by S. Demers
© Springer-Verlag Berlin Heidelberg 1991