Chapter 7
Water Constituents Assessment at the Sassandra
River Mouth (Côte d’Ivoire): An Outline Based
on Remote Sensing Reflectances
Eric V. Djagoua, Jeanne M. Kouadio, Cassandre Z. Dro, Mireille Bella,
Jean B. Kassi, Brice A. Mobio, Kouadio Affian, Simon Belanger
and Pierre Larouche
Abstract Optical remote sensing of surface waters has been used to monitor the
impact of the Sassandra River—one of the four main rivers of Côte d’Ivoire—along
the coast of the Gulf of Guinea. A 5-year (2003–2007) series of Sea-viewing Wide
Field-of-view Sensor (SeaWiFS) images was chosen to identify (spectrally) the major
constituents of coastal waters under the influence of river discharges. The percent
contributions of yellow substance, i.e. coloured dissolved organic matter (CDOM),
chlorophyll-like pigments of phytoplankton (CHL) and suspended detritus (DET )
to the total reflectance (approximated by the sum of reflectances at 443, 555 and
670 nm) were calculated. Ternary plots of these percentages provided some general
indications about the relative proportions of CDOM, CHL and DET, according to
the impact attributed to each water constituent. The analysis showed that water
constituents follow trends linked to the “marine” seasons of the area. The CHL and
DET contributions seem to correlate with the timing of cooler (upwelling) periods,
while CDOM seems to correlate better with that of warmer periods. The relationship
with the Sassandra river runoff is not as evident, even though CDOM increased
contributions appear to mirror the weakening of upwelling and the discharge of
local rivers. This broad ecosystem outline should be extended to the entire Côte
E. V. Djagoua () · J. M. Kouadio · C. Z. Dro · M. Bella · J. B. Kassi · B. A. Mobio · K. Affian
Centre Universitaire de Recherche et d’application en Télédétection (CURAT),
Université de Cocody, Abidjan, Côte d’Ivoire
e-mail: vdjagoua@yahoo.fr
K. Affian
Laboratoire de Géologie Marine et de Sédimentologie,
U.F.R. des Sciences de la Terre et des Ressources Minières,
Université de Cocody, Abidjan, Côte d’Ivoire
S. Belanger
Laboratoire d’optique Aquatique et de Télédétection (AquaTel),
Université de Québec à Rimouski (UQAR), Rimouski (Québec), Canada
P. Larouche
Maurice Lamontagne Institute, Fisheries and Oceans Canada,
Mont Joli (Québec), Canada
V. Barale, M. Gade (eds.), Remote Sensing of the African Seas,
135
DOI 10.1007/978-94-017-8008-7_7,
© Springer Science+Business Media Dordrecht 2014
Water Constituents Assessment at the Sassandra
River Mouth (Côte d’Ivoire): An Outline Based
on Remote Sensing Reflectances
Eric V. Djagoua, Jeanne M. Kouadio, Cassandre Z. Dro, Mireille Bella,
Jean B. Kassi, Brice A. Mobio, Kouadio Affian, Simon Belanger
and Pierre Larouche
Abstract Optical remote sensing of surface waters has been used to monitor the
impact of the Sassandra River—one of the four main rivers of Côte d’Ivoire—along
the coast of the Gulf of Guinea. A 5-year (2003–2007) series of Sea-viewing Wide
Field-of-view Sensor (SeaWiFS) images was chosen to identify (spectrally) the major
constituents of coastal waters under the influence of river discharges. The percent
contributions of yellow substance, i.e. coloured dissolved organic matter (CDOM),
chlorophyll-like pigments of phytoplankton (CHL) and suspended detritus (DET )
to the total reflectance (approximated by the sum of reflectances at 443, 555 and
670 nm) were calculated. Ternary plots of these percentages provided some general
indications about the relative proportions of CDOM, CHL and DET, according to
the impact attributed to each water constituent. The analysis showed that water
constituents follow trends linked to the “marine” seasons of the area. The CHL and
DET contributions seem to correlate with the timing of cooler (upwelling) periods,
while CDOM seems to correlate better with that of warmer periods. The relationship
with the Sassandra river runoff is not as evident, even though CDOM increased
contributions appear to mirror the weakening of upwelling and the discharge of
local rivers. This broad ecosystem outline should be extended to the entire Côte
E. V. Djagoua () · J. M. Kouadio · C. Z. Dro · M. Bella · J. B. Kassi · B. A. Mobio · K. Affian
Centre Universitaire de Recherche et d’application en Télédétection (CURAT),
Université de Cocody, Abidjan, Côte d’Ivoire
e-mail: vdjagoua@yahoo.fr
K. Affian
Laboratoire de Géologie Marine et de Sédimentologie,
U.F.R. des Sciences de la Terre et des Ressources Minières,
Université de Cocody, Abidjan, Côte d’Ivoire
S. Belanger
Laboratoire d’optique Aquatique et de Télédétection (AquaTel),
Université de Québec à Rimouski (UQAR), Rimouski (Québec), Canada
P. Larouche
Maurice Lamontagne Institute, Fisheries and Oceans Canada,
Mont Joli (Québec), Canada
V. Barale, M. Gade (eds.), Remote Sensing of the African Seas,
135
DOI 10.1007/978-94-017-8008-7_7,
© Springer Science+Business Media Dordrecht 2014