Understanding the potential and limitations of
solar-induced fluorescent imaging of cyanobacteria in oceans
Daoxi Zhang (Supervisors: Jan-Peter Muller, Dave Walton & Samantha Lavender)
Mullard Space Science Laboratory, UCL Department of Space and Climate Physics,
Holmbury St. Mary, Dorking, Surrey, United Kingdom, RH5 6NT
daz@mssl.ucl.ac.uk
1.  Outline
  Fluorescence Line Height
We present observations of cyanobacterial fluorescence images derived
from MERIS products. Firstly, we present a brief introduction to
cyanobacteria and their significance in oceans for climate studies. This
includes fluorescence line height (FLH) and maximum chlorophyll index
(MCI) and their applications in terms of detecting different Plankton types in
the ocean. The research methodology about mapping cyanobacteria is then
described. Finally, the fluorescence images of cyanobacteria on the west
coast of Canada are present.
The Fluorescence Line Height (FLH) algorithm measures the height of the
phytoplankton chlorophyll fluorescence peak near 680nm above a
linear baseline. It is calculated as the radiance in band 8 (685nm) above a
baseline formed by linear interpolation between the radiances in band 7
(665nm) and band 9 (709nm)[6].
2.  Introduction to cyanobacteria
Cyanobacteria are photosynthetic microorganisms which possess the
ability to synthesize chlorophyll A[1]. Due to their ability to form the
phycobilin pigment[1], which causes the bluish colour of the organisms
when it is in high concentration, they also commonly known as blue-green
algae. Even though many species of cyanobacteria are able to live in soil
and terrestrial habitats, the primary environments which they colonise are
marine and freshwater[2].
The morphology of cyanobacteria includes unicellular, colonial and
multicellular filamentous forms[2]. The following pictures[1] show examples
of each of these forms,
(a) unicellular
(b) colonial
Fig.2[7]. Index values and bands used for the FLH algorithm.
  Maximum Chlorophyll Index
Fig.3[5]. FLH spectral signatures of chlorophyll models at varying
concentrations. The black horizontal bars display positions and widths of
MERIS spectral bands.
The Maximum Chlorophyll Index (MCI) algorithm measures the height of the
phytoplankton chlorophyll fluorescence peak near 705nm above a linear
baseline. The method for calculating MCI is analogous to that of FLH with
the only difference being the bands utilized to create the baseline. It is
calculated as the radiance in band 9 (709nm) above a baseline formed by
linear interpolation between the radiances in band 8 (681nm) and band 10
(753nm).
(c) multicellular
3.  The importance of cyanobacteria in oceans for climate studies
Fig.4[7]. Index values and bands used for the MCI algorithm.
i.  Understanding the Carbon cycle
-Cyanobacteria absorb CO2 and produce O2
-40% of the carbon in the Earth’s carbon cycle is reused and recycled
by these tiny creatures[3]
ii.  Understanding the role of aerosols and clouds in the climate system
-Cyanobacteria produce DMSP:
(Dimethyl Sulfoniopropionate)
which in turn results in DMS (DiMethyl Sulphide):
DMS form aerosols which become
UV
CCNs for cloud formation
Aerosol produc,on
Fig.5[5]. MCI spectral signatures of chlorophyll models at varying
concentrations. As chlorophyll concentration increases, the
fluorescence peak near 705nm becomes increasingly prevalent. The
black horizontal bars display positions and widths of MERIS spectral
bands.
5.  Result
We made use of MERIS L2 data on Vancouver Island acquired on the 5th of
September 2002 . This includes exposed waters on the south- west coast and
sheltered waters to the north and east along with the Strait of Georgia and
other straits and inlets. The FLH and MCI images are derived from the data of
this region are shown as follows:
Chlorophyll Fluorescence
-Climate Feedback
iii.  Heating effects
-Cyanobacterial blooms can cause
Sea Surface Temperature (SST)
increase by absorbing and scattering
light
Cyanobacteria
DMS
DMSP
Fig. 1. The procedure of DMS formation originated from
DMSP produced by Cyanobacteria in water under UV
stressed
4.  Fluorescence Line Height & Maximum Chlorophyll Index
  MERIS
The Medium Resolution Imaging Spectrometer (MERIS) remote sensing
instrument is used to acquire spectral information about the Earth’s
surface[4]. It is a passive sensor mounted on the ENVISAT satellite that
relies on solar radiation as its source of energy. In terms of an Ocean
Mission, the primary contributions of MERIS products to ocean studies
comprise estimation of photosynthetic potential by mapping of
phytoplankton; dissolved organic material (also known as yellow
substance or gelbstoff), and of suspended sediments[4].
Fig. 6. Fluorescence signal calculated from bands 7, 8 and 9 of MERIS L2
data. Values are increased in areas of high sediment load in the Fraser River
plume and at the heads of inlets. Clouds and land are masked to black.
Fig. 7. Maximum Chlorophyll Index computed from bands 8, 9 and 10 of
MERIS L2 data, showing part of the area of Fig. 6. Clouds and land are
masked to black as before. Small areas of high MCI (yellow, red, white) can
be seen along the coast and offshore.
6. Discussion and Conclusions
As we can see from the FLH image, the distribution and concentration of
chlorophyll a of cyanobacteria on the west coast of Canada is displayed.
Whereas, the MCI image can be interpreted as areas of either intense
plankton blooms or of attached benthic vegetation. Comparing FLH and MCI
images, it is found that values of Fluorescence Line Height are low when
values of MCI are high. These results provide valuable information that may
be used to monitor cyanobacterial blooms and red tides.
The predominant features of MERIS in the remote sensing areas are the
Fluorescence Line Height (FLH) and Maximum Chlorophyll Index (MCI)
algorithms[5] which measure the height of the chlorophyll in phytoplankton
that fluorescence peak above a linear baseline 685nm and 705nm,
respectively.
Reference:
[1]. Whitton, B.A., Potts, M. The Ecology Of Cyanobacteria:Their Diversity In Time And Space. (2000) pp. 1-2
[2]. Chorus, I., Bartram, J.. Toxic cyanobacteria in water: a guide to their public health consequences, monitoring and
management. (1999) pp.16-18
[3]. ScienceDaily, 8 March 2010, http://www.sciencedaily.com/releases/2010/03/100304142247.htm
[4]. European Space Agency. 2006. MERIS Product Handbook, Issue 2.1. Retrieved 4 May 2009
[5]. Statham. Sara Statham's MERIS primer. (2009) pp. 1-12
[6]. Gower, J., L. Brown and G. Borstad. 2004. Observation of chlorophyll fluorescence in west coast waters of
Canada using the MODIS satellite sensor. Canadian Journal of Remote Sensing. 30(1): 17-25.
[7]. Gower, J., R. Doerffer and G.A. Borstad. 1999. Interpretation of the 685 nm peak in water- leaving radiance
spectra in terms of fluorescence, absorption and scattering, and its observation by MERIS. International Journal of
Remote Sensing. 9: 1771-1786.