52
J. Gower and S. King
We discuss above our reasons for believing that spectra shown in this chapter are
from Trichodesmium. Pelagic Sargassum does not appear to be common in African
waters. We have evidence for an occurrence in Sierra Leone following the equatorial
Atlantic Sargassum event in the summer of 2011, but this appears to be unusual.
2.10 Summary and Conclusions
Ocean colour data from satellites now provide a valuable source of information on
spatial and temporal patterns for all oceans and coastal waters of the world. Studies
of African waters can be expected to especially benefit from satellite data, because
of the lack of local observing facilities and supporting infra-structure, and the danger
of piracy in some areas.
We hope that satellite water colour coverage will continue, though the recent loss
of MERIS reminds us of the risk of a data gap in time. At present, images cover
space scales from kilometers to global, and time scales from daily to the 15-year
period for which data have been provided since 1997 by SeaWiFS, MODIS, MERIS
and VIIRS. Other options, not considered here, include information on longer term
trends that can be deduced by comparison of recent data with results from the CZCS
(1978–1986), and the use of finer scale data from higher resolution, but less sensitive,
imagers such as Landsat MSS or TM. Spatial resolution can be extended down to a
scale of meters using commercial mapping sensors.
The fluorescence data from MODIS and MERIS are useful to confirm the chlorophyll values available through the green to blue ratio method. Examples are given in
Figs. 2.2, 2.4, 2.5 and 2.6 above. Here we find that normalization of FLH as conventionally carried out, is not appropriate, in that un-normalized FLH provides a good
measure of chlorophyll.
MERIS, through the spectral band at 709 nm, provided the added capability of
detecting blooms using the MCI index. We would like to continue time series such
as Figs. 2.10, 2.11, 2.12, 2.14, 2.16 and 2.19 indefinitely into the future, but there is
now a data gap until the launch of ESA’s Sentinel 3 satellite, planned for 2014.
Acknowledgments This work was supported by the Canadian federal Department of Fisheries and
Oceans, and by the Canadian Space Agency. MODIS satellite data are made available by NASA,
the US National Aeronautics and Space Administration. MERIS image data are made available by
the European Space Agency, ESA. Time series analysis of MERIS data is made possible by the
G-POD system of ESA. Some analyses and visualizations used in this study were produced with
the Giovanni online data system, developed and maintained by the NASA GES DISC.
References
Abbott MR, Letelier RM (1999) Algorithm theoretical basis document chlorophyll fluorescence,
MODIS product number 20, NASA. http://modis.gsfc.nasa.gov/data/atbd/atbd_mod22.pdf.
Accessed 27 Dec 2013
Acker JG, Leptoukh G (2007) Online analysis enhances use of NASA earth science data. Eos Trans
AGU 88(2):14–17
J. Gower and S. King
We discuss above our reasons for believing that spectra shown in this chapter are
from Trichodesmium. Pelagic Sargassum does not appear to be common in African
waters. We have evidence for an occurrence in Sierra Leone following the equatorial
Atlantic Sargassum event in the summer of 2011, but this appears to be unusual.
2.10 Summary and Conclusions
Ocean colour data from satellites now provide a valuable source of information on
spatial and temporal patterns for all oceans and coastal waters of the world. Studies
of African waters can be expected to especially benefit from satellite data, because
of the lack of local observing facilities and supporting infra-structure, and the danger
of piracy in some areas.
We hope that satellite water colour coverage will continue, though the recent loss
of MERIS reminds us of the risk of a data gap in time. At present, images cover
space scales from kilometers to global, and time scales from daily to the 15-year
period for which data have been provided since 1997 by SeaWiFS, MODIS, MERIS
and VIIRS. Other options, not considered here, include information on longer term
trends that can be deduced by comparison of recent data with results from the CZCS
(1978–1986), and the use of finer scale data from higher resolution, but less sensitive,
imagers such as Landsat MSS or TM. Spatial resolution can be extended down to a
scale of meters using commercial mapping sensors.
The fluorescence data from MODIS and MERIS are useful to confirm the chlorophyll values available through the green to blue ratio method. Examples are given in
Figs. 2.2, 2.4, 2.5 and 2.6 above. Here we find that normalization of FLH as conventionally carried out, is not appropriate, in that un-normalized FLH provides a good
measure of chlorophyll.
MERIS, through the spectral band at 709 nm, provided the added capability of
detecting blooms using the MCI index. We would like to continue time series such
as Figs. 2.10, 2.11, 2.12, 2.14, 2.16 and 2.19 indefinitely into the future, but there is
now a data gap until the launch of ESA’s Sentinel 3 satellite, planned for 2014.
Acknowledgments This work was supported by the Canadian federal Department of Fisheries and
Oceans, and by the Canadian Space Agency. MODIS satellite data are made available by NASA,
the US National Aeronautics and Space Administration. MERIS image data are made available by
the European Space Agency, ESA. Time series analysis of MERIS data is made possible by the
G-POD system of ESA. Some analyses and visualizations used in this study were produced with
the Giovanni online data system, developed and maintained by the NASA GES DISC.
References
Abbott MR, Letelier RM (1999) Algorithm theoretical basis document chlorophyll fluorescence,
MODIS product number 20, NASA. http://modis.gsfc.nasa.gov/data/atbd/atbd_mod22.pdf.
Accessed 27 Dec 2013
Acker JG, Leptoukh G (2007) Online analysis enhances use of NASA earth science data. Eos Trans
AGU 88(2):14–17