Antonio Ruiz Verdú, Centre for Hydrographic Studies, CEDEX. Madrid. Spain 30 th Congress of the International Association of Theoretical and Applied Limnology

MONITORING CYANOBACTERIA IN MONITORING CYANOBACTERIA IN INLAND WATERS BY REMOTE SENSINGINLAND WATERS BY REMOTE SENSING

Antonio Antonio RuizRuiz VerdúVerdú,,

Centre for Hydrographic Studies, CEDEX. Madrid. SpainCentre for Hydrographic Studies, CEDEX. Madrid. Spain

3030thth Congress of the International Association of Theoretical and Applied Congress of the International Association of Theoretical and Applied Limnology. 12-18 August 2007. Montreal, CanadaLimnology. 12-18 August 2007. Montreal, Canada

1. Reflectance spectra of Spanish inland waters

2. Phycocyanin (PC) as an indicator of cyanobacterial biomass

3. Approaches for PC estimation from remotely sensed data

4. Validation of algorithms in Spain5. Examples of applications (thematic

maps)

SUMMARY

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lect

anci

a (R

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Reflectance spectra: Optical signature of natural waters

Reflectance spectra of Spanish inland waters

Examples of reflectance spectra for waters dominated by a single phytoplankton group (>90% of biovolume)

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Wavelength (nm)

R(

) / R

(67

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R(

) / R

(67

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R(

) / R

(67

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R(

) / R

(67

5)

Chlorophyceae Bacillariophyceae

Cryptophyceae CYANOBACTERIA

Chl-a

Phycocyanin

Reflectance spectra of cyanobacterial blooms (July 2007, Spain)

• Phycocyanin (PC) is a characteristic pigment of Cyanobacteria

• PC could be used as a proxy for cyanobacterial biomass

• PC absorption is noticeable in reflectance spectra (at around 625 nm)

• If adequate spectral bands are present, algorithms could be developed for PC retrieval from spaceborne sensors

• Envisat-MERIS (ESA) is currently the only operational spaceborne sensor capable of retrieving PC

Remote sensing of Cyanobacteria

Main facts:

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Cyanobacte ria l chlorophyll a (mg m-3)

PC

AV

G (m

g m

-3)

y = 2.1412x

R2 = 0.9027

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Cyanobacte ria l chlorophyll a (mg m-3)

PC

AV

G (m

g m

-3)

y = 2.1412x

R2 = 0.9027

1 0

PC as a proxy for cyanobacterial biomass

• Intracellular PC content in Cyanobacteria is typically higher than Chl-a

• BUT, PC:Chl-a ratios are not constant

• If Cyanobacteria are not dominant, the variability of PC:Chl-a ratios is higher

• HOWEVER, in the studied reservoirs in Spain, PC:Chl-a ratios are relatively constant for [Chl-a] > 2 mg m-3

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Abso

rpti

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oeffi

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Chl-Chl-aa

PCPCCarotenoidCarotenoid

ss

Chl-Chl-aa

Particle scatteringParticle scattering

Retrieving PC absorption from reflectance at 620 nm

• PC absorption can be detected in R spectra• BUT, other pigments absorb as well (mainly Chl-a and Chl-b)

Chl-a

Chl-b

Chl-cPC

Relative pigment absorption

• Absorption of CDOM and detritus at 620 nm is often low but not negligible

Approaches for algorithm development

1. BAND RATIO

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R(2)R(1)

R(1) = Reflectance at absorption band

R(2) = Reflectance at reference band (no PC absorption)

[PC] = f [R([PC] = f [R(11) / R() / R(22)])]


2. BASELINE

R(1) = Reflectance at absorption band

R(2) = Reflectance at reference band 1 (no PC absorption)

R(3) = Reflectance at reference band 1 (no PC absorption)

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R(2)R(1)

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[PC] = f {0.5 x [R ([PC] = f {0.5 x [R (11) + R () + R (33)] - R ()] - R (22)})}


3. NESTED BAND RATIO (Simis et al., 2005)

• Developed for MERIS bands

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M6 M7 M9 M12

• Backscattering is calculated from band 12

• Chl-a absorption is calculated from the ratio of bands 7 and 9

• PC absorption is calculated from the ratio of bands 6 and 9 and corrected with the estimated chl-a absorption at 620 nm

• [PC] is calculated from PC absorption

Simis, S. G. H., S. W. M. Peters, & H. J. Gons. (2005). Limnology and Oceanography, 50, 237-245.

Validation of PC algorithms• 65 reservoirs and lakes sampled in the period 2001-2007 in Spain (200 sampling points)

• Concurrent field measurements:

• Optical (reflectance, absorption…)• Pigment quantification• Taxonomic• Image processing

Validation of PC algorithms

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PC measured (PCREF mg m-3)

PC r

etri

eved

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RA

D ,

mg

m-3

)

Simis et al. (2005) algorithm

R2=0.94p<0.001

Validation of PC algorithms

• Simis algorithm has been validated with a common dataset from Spanish and Dutch inland water bodies

• The influence of other pigments in the algorithm has been investigated

• Comparison with other published algorithms is currently ongoing

Simis, S.G.H., A. Ruiz-Verdú, J.A. Domínguez-Gómez, R. Peña-Martinez, S.W.M. Peters, and H.J. Gons. (2007). Remote Sensing of Environment 106, 414–427.

Obtaining maps for Chl-a and PC

• PC and Chl-a algorithms have been applied to MERIS and Chris/Proba imagery

• Chris/Proba: Experimental ESA satellite

- 18 bands (similar to MERIS) - 17 m spatial resolution (MERIS=300 m) - Limited number of images

• Major requirement: An accurate atmospheric correction method is needed

MERIS IMAGERY OVER ALBUFERA DE VALENCIA LAKE

Visible bandsVisible bands IR / VIS bandsIR / VIS bands


CHRIS/PROBA IMAGERY OVER ALBUFERA DE VALENCIA LAKE


Visible bandsVisible bands


[PC] (mg/m3)0 50 100 150 250 <255

[PC] (mg/m3)0 50 100 150 250 <255

[PC] (mg/m3)0 50 100 150 250 <255

PCPC March 1 March 1stst 2007 2007

[Cla] (mg/m3)0 50 100 150 250 <255

[Cla] (mg/m3)0 50 100 150 250 <255

[Cla] (mg/m3)0 50 100 150 250 <255

Chl-aChl-a March 1 March 1stst 2007 2007

0 20 60 100 140 180 220 >250 mg m-30 20 60 100 140 180 220 >250 mg m-3

CHRIS / PROBACHRIS / PROBA

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Chl-aChl-a June 24 June 24thth 2007 2007 PCPC June 24 June 24thth 2007 2007

MERISMERIS

Obtaining maps for Chl-a and PCEVOLUTION OF MEASURED AND ESTIMATED PHYCOCYANIN (SAMPLING POINT B )

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22/04/2004 22/05/2004 21/06/2004 21/07/2004 20/08/2004 19/09/2004 19/10/2004 18/11/2004

DATE

PC

(m

g m

-3)

MEASURED PCESTIMATED PC

Monitoring a eutrophic reservoir: Rosarito

• Cyanobacterial biomass can be monitored from spaceborne sensors, by detecting the pigment Phycocyanin (PC)

• MERIS and CHRIS/PROBA imagery have been used successfully in Spanish lakes and reservoirs

• Algorithms are less accurate for low PC concentrations (i.e. early bloom stages)

MAIN CONCLUSIONS

MONITORING CYANOBACTERIA IN MONITORING CYANOBACTERIA IN INLAND WATERS BY REMOTE SENSINGINLAND WATERS BY REMOTE SENSING

Antonio Antonio RuizRuiz VerdúVerdú, Ramón Peña Martínez and Caridad De Hoyos , Ramón Peña Martínez and Caridad De Hoyos AlonsoAlonso

Centre for Hydrographic Studies, CEDEX. Madrid. SpainCentre for Hydrographic Studies, CEDEX. Madrid. Spain

3030thth Congress of the International Association of Theoretical and Applied Congress of the International Association of Theoretical and Applied Limnology. 12-18 August 2007. Montreal, CanadaLimnology. 12-18 August 2007. Montreal, Canada

Documents

Antonio Ruiz Verdú, Centre for Hydrographic Studies, CEDEX. Madrid. Spain 30 th Congress of the International Association of Theoretical and Applied Limnology