Environmental Engineering Reference
In-Depth Information
Becker et al.
2009
; Hunter et al.
2010
). Remote sensing is currently used to monitor
broad changes in phytoplankton communities, exploiting the spectral dissimilari-
ties of brown, green, blue-green and red algae in inland waters. This technique is
an extremely useful tool for limnological research and water resource management
(Hunter et al.
2008
). Water quality (Secchi depth,
K
d
in PAR, tripton, CDOM) and
substrate cover type (seagrass, algae, sand) parameters, which vary in sub-tropical
and tropical coastal environments may also affect the satellite image data (Phinn
et al.
2005
) and can thus influence the remote sensing information. A combination of
a chlorophyll anomaly (spectral shape at 490 nm) and a backscatter ratio can provide
an improvement in satellite detection of the toxic dinoflagellate
Karenia brevis
. It
is possible to increase the detection accuracy by 30-50 % in seawaters (Tomlinson
et al.
2009
; Cannizzaro et al.
2008
). The remote sensing application has also been
used to characterize high concentrations of suspended sediment and to map chloro-
phyll
a
(Chl
a
) or phytoplankton and non-phytoplankton suspended matter distribu-
tion in lakes and oceans (Ferreira et al.
2009
; Cannizzaro and Carder
2006
; Gons
et al.
2008
; Oyama et al.
2009
; González Vilas et al.
2011
).
The ocean color depends on the optical variables (Coble
2007
; Del Castillo and
Miller
2008
; Carder et al.
1991
; Hoge et al.
1995
; Hoge et al.
2001
; Sathyendranath
et al.
1989
; Stramski et al.
2001
; Brown et al.
2008
; Mélin et al.
2007
; Lee et al.
1994
; Kahru and Mitchell
2001
; Siegel et al.
2002
; Nair et al.
2008
; Siegel et al.
2005
). The key factors are (i) phytoplankton species (or algae) and their variability;
(ii) the amount of colored DOM; (iii) the amount and size of organic particles; (iv)
the contents of inorganic particles (tripton); and (v) water itself. CDOM can be esti-
mated by using ocean color with various levels of success (del Castillo and Miller
2008
; Carder et al.
1999
; Hoge et al.
1995
; Hoge et al.
2001
; Lee et al.
1994
; Kahru
and Mitchell
2001
; Siegel et al.
2002
; Siegel et al.
2005
). In open ocean waters,
far from the influence of terrestrial runoff that mainly affects coastal waters (case
1 waters), the spectral quality and intensity of light leaving the ocean depends first
of all on the concentration of phytoplankton (Morel and Prieur
1977
; Morel
1980
).
Empirical algorithms of ocean color based on blue-to-green ratios are used to esti-
mate the chlorophyll
a
concentration within the upper layer of the water column
(McClain et al.
2004
; O'Reilly et al.
1998
; Harding et al.
2005
). The second-order
variability for given chlorophyll levels depends on two main sources: (i) the amount
of non-algal absorption, especially due to colored dissolved organic matter; and
(ii) the amplitude of the backscattering coefficient of particles (Brown et al.
2008
).
Remote sensing of surface waters in the open ocean (case 2 waters) could be used
in conjunction with the inversion of UV-blue wavelengths, to separate the contri-
bution of non-algal particles and of colored dissolved organic matter to the total
light absorption, and to monitor non-algal suspended particle concentration and dis-
tribution (Tzortziou et al.
2007
). It is shown that phytoplankton typically absorbs
strongly in the blue and weakly in the green. CDOM absorption thus overlaps to
that of phytoplankton and non-algal particulate matter in the blue part of the visible
spectrum. This issue might affect the primary productivity and the remote sensing
estimation of phytoplankton biomass and of total suspended matter concentration
(Zhang et al.
2009
; Carder et al.
1991
; Doxaran et al.
2002
).
