Monitoring algal blooms using the MERIS Maximum Chlorophyll Index

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1 Monitoring algal blooms using the MERIS Maximum Chlorophyll Index Caren Binding & Tracie Greenberg, Bob Bukata, Sue Watson, Shannah Rastin, Jess Gould Workshop for Remote Sensing of Coastal and Inland Waters University of Wisconsin-Madison, June

2 The MERIS Maximum Chlorophyll Index Remote Sensing Reflectance MCI Peak Wavelength MCI Slope (79-681) MERIS MCI L 79 - L (L753 - L 681) ( )

3 The MERIS Maximum Chlorophyll Index Remote Sensing Reflectance MCI Peak Wavelength MCI Slope (79-681) MERIS MCI L 79 - L (L753 - L 681) ( )

4 Lake of the Woods 95 '"W 94 '"W Lake 5 '"N Winnipeg Kilometers Chlorophyll up to 3 g L-1 Great Lakes Ottawa Ottawa! )" Ontario Manitoba Optically & hydrologically complex CANADA U.S.A Washington D.C.! Very high DOC (acdom 2-3 m-1) 49 '"N MERIS/MODIS Chl retrievals fail Minnesota 49 '"N Lake of the Woods 95 '"W 94 '"W

5 Lake of the Woods 95 '"W 94 '"W Lake 5 '"N Winnipeg Kilometers Chlorophyll up to 3 g L-1 Great Lakes Ottawa Ottawa! )" Ontario Manitoba Optically & hydrologically complex CANADA U.S.A Washington D.C.! Very high DOC (acdom 2-3 m-1) 49 '"N MERIS/MODIS Chl retrievals fail Minnesota 49 '"N Lake of the Woods 95 '"W 94 '"W

6 MERIS Rw during intense blooms All pixels flagged as turbid.1 Bright Pixel Atmospheric Correction Large over-correction & negative L2 Rw Non-zero NIR L1 R due to algae rather than mineral, with peak at 78 nm -1 MERIS L2 Rlw (sr ) Wavelength (nm) 68 nm 78 nm 778 nm L1 Radiance mw/(m^2 sr nm)

7 MERIS Rw during intense blooms All pixels flagged as turbid.1 Bright Pixel Atmospheric Correction Large over-correction & negative L2 Rw Non-zero NIR L1 R due to algae rather than mineral, with peak at 78 nm -1 MERIS L2 Rlw (sr ) Wavelength (nm) 68 nm 78 nm 778 nm L1 Radiance mw/(m^2 sr nm)

8 Assessing MERIS Algal Products L1b True Colour Algal_2 C2R Chl C2R Eutrophic C2R Boreal L1B MCI L2 MCI FLH Relationship with Chl i R 2 RMSE (%) L2 Algal_2 Chl i =.375Chl M C2R Chl_conc Chl i =.664Chl M C2R w. ICOL Chl_con Chl i = 1.892Chl M C2R Eutrophic Lake Chl i = -.129Chl M C2R Boreal Lake Chl i =.444Chl M L1b MCI Chl i = 6.166MCI L1b MCI w. ICOL Chl i = 6.25MCI L2 MCI Chl i = 1457MCI L2 FLH Chl i = -2491FLH

9 Assessing MERIS Algal Products L1b True Colour Algal_2 C2R Chl C2R Eutrophic C2R Boreal L1B MCI L2 MCI FLH Relationship with Chl i R 2 RMSE (%) L2 Algal_2 Chl i =.375Chl M C2R Chl_conc Chl i =.664Chl M C2R w. ICOL Chl_con Chl i = 1.892Chl M C2R Eutrophic Lake Chl i = -.129Chl M C2R Boreal Lake Chl i =.444Chl M L1b MCI Chl i = 6.166MCI L1b MCI w. ICOL Chl i = 6.25MCI L2 MCI Chl i = 1457MCI L2 FLH Chl i = -2491FLH

10 1 A S O Inter-annual Bloom Monitoring Monitoring lake trophic status, and relating timing, intensity and extent of blooms to climate variables and loadings Chlorophyll (mg m -3 ) Bloom aerial extent (% of open water) J J A S O J J A S O J J A S O J J A S J J A S O J J A S O J J A S O J J A S O J J A S O 1 % Chl < 8 mg m-3 % Chl 8-25 mg m-3 % Chl > 25 mg m-3 Binding et al. (211) J. Plankton Res.

11 1 A S O Inter-annual Bloom Monitoring Monitoring lake trophic status, and relating timing, intensity and extent of blooms to climate variables and loadings Chlorophyll (mg m -3 ) Bloom aerial extent (% of open water) J J A S O J J A S O J J A S O J J A S J J A S O J J A S O J J A S O J J A S O J J A S O 1 % Chl < 8 mg m-3 % Chl 8-25 mg m-3 % Chl > 25 mg m-3 Binding et al. (211) J. Plankton Res.

12 Winter Diatom Blooms on Lake Erie Winter blooms of Diatom Aulacoseira on Lake Erie with chlorophyll concentrations up to 1 g L -1 L1 MCI detects blooms within and surrounding surface ice

13 Winter Diatom Blooms on Lake Erie Winter blooms of Diatom Aulacoseira on Lake Erie with chlorophyll concentrations up to 1 g L -1 L1 MCI detects blooms within and surrounding surface ice

14 Winter Diatom Blooms on Lake Erie Radiance Difference (mw m -2 sr -1 nm -1 ) Radiance Difference Diatom Absorption Normalised Absorption (dl) Difference between clean ice and bloom ice signal produces radiance in agreement with absorption spectrum of chlorophyll-a Wavelength (nm) Location of blooms within ice in agreement with in situ chlorophyll determinations along cruise track MCI (mw m -2 sr -1 nm -1 ) Station No ICE MCI WATER MCI 9 CHLA Distance (pixels) Extracted in situ Chl (mg m -3 )

15 Winter Diatom Blooms on Lake Erie Radiance Difference (mw m -2 sr -1 nm -1 ) Radiance Difference Diatom Absorption Normalised Absorption (dl) Difference between clean ice and bloom ice signal produces radiance in agreement with absorption spectrum of chlorophyll-a Wavelength (nm) Location of blooms within ice in agreement with in situ chlorophyll determinations along cruise track MCI (mw m -2 sr -1 nm -1 ) Station No ICE MCI WATER MCI 9 CHLA Distance (pixels) Extracted in situ Chl (mg m -3 )

16 Sensitivity of MCI to Mineral Sediments Bloom Mineral Sediments L1 MCI (mw m -2 sr -1 nm -1 ) October 8th 211 First impressions MCI not overly sensitive to mineral scattering

17 Modelling Sediment Sensitivity MCI MSPM = MSPM = 5 MSPM =1 MSPM= Chl Hydrolight modelling to determine effects of sediments on MCI properties peak and slope MSPM = MSPM = 5 MSPM =1 MSPM=2 Slope Chl

18 Modelling Sediment Sensitivity MCI MSPM = MSPM = 5 MSPM =1 MSPM= Chl Hydrolight modelling to determine effects of sediments on MCI properties peak and slope Exploring use of LUT with peak and slope to extract CHL under high MSPM Slope MSPM = MSPM = 5 MSPM =1 MSPM= Chl Slope MSPM MCI CHL

19 MERIS MCI Summary Effective for Chl > 1 g L -1, migration of peak to FLH bands at lower Chl Detecting only surface blooms because of low penetration depth Fairly insensitive to CDOM, bottom reflectance, and failures in atmospheric correction Limited influence of mineral scattering under intense bloom conditions - Influence of MSPM most pronounced in slope parameter

20 MERIS MCI Summary Effective for Chl > 1 g L -1, migration of peak to FLH bands at lower Chl Detecting only surface blooms because of low penetration depth Fairly insensitive to CDOM, bottom reflectance, and failures in atmospheric correction Limited influence of mineral scattering under intense bloom conditions - Influence of MSPM most pronounced in slope parameter