# Presentation: 732286

## Effects of Fluorescence Self Absorption of Algae in Sea Water

-   **Candy Barbaran**
- Annie Becerra
- Mentors: Prof. Fred Moshary
- 	Dr. Alex Gilerson

***NYCRI***

## Background

- Satellite imagery of ocean color provides important information about water quality and composition.
- Abundance of phytoplankton (algae) in the ocean can be traced by _Chlorophyll A_ concentration  which exists in all types of algae and has distinct spectral features.
- Part of the light energy absorbed by algae in blue-green emits in the red as chlorophyll fluorescence.
- Chlorophyll fluorescence is a vital parameter which can be considered as an indicator of chlorophyll concentration and photosynthetic activity in the ocean.

##    Analyze the spectral shape of chlorophyll fluorescence and absorption in order to detect patterns in the fluorescence spectral shift -  detecting patterns in the spectral shift will allow us to eliminate all other factors and measure pure fluorescence.

**Goal**** **
- Improve algorithms for instruments aboard satellites in order to make fluorescence measurements of algae more accurate.

**Purpose of the experiment**

## Water Composition for Open Ocean and Coastal Waters

**Algae**

**Algae**
**Colored Dissolved Organic Matter (CDOM)**
- Minerals

- Open ocean

- Coastal waters

## Challenges of Using Chlorophyll Fluorescence Methods For Algae Detection

- Fluorescence overlaps with the other spectral features. Special algorithms are needed to separate fluorescence from self absorption and elastic reflectance .

- Sea surface

- Depth

## Fluorescence Magnitude and Peak over Baseline

**Fluorescence Magnitude and Peak over Baseline**

- Reflectance of the sun

- Reflectance of the sun with fluorescence

**            ****Reflectance=   **

**            ****Eu/Ed~b****b ****/a**

## WET Labs AC-S Instrument

**The AC-S instrument measures absorption and attenuation at 82 wavelengths from 400 to 750 nm**

## Algae absorption measured by WET Labs ACS instrument

- There is strong algae absorption in the fluorescence zone which causes change of fluorescence spectra

## Changes of the fluorescence spectral shape due to algae absorption

- Fl(λ)~(1/r2)*Fl0(λ)*exp(-a(λ)*h)

**h**

**r**

## Experimental Setup for the Measurements of Fluorescence Spectral Shape

**Objects tested: algae *****Isochrysis sp.,***** *****Tetraselmis striata*****, **
**concentrations up to 4x10****6**** cells/mL with necessary dilutions**

-  Algae are illuminated by the laser light at different depths. Emitted fluorescence is partially absorbed during propagation through algae.
-  Spectral shape of fluorescence is measured by fiber optic sensor connected to the Ocean Optics spectrometer

## Shift of fluorescence of Algae Isochrysis as a function of depth under 488nm excitation

- Fluorescence spectra for different excitation depths

- Shift of fluorescence maximum for various excitation depths

**Algae absorption peak**

## Shift of Fluorescence of Tetraselmis striata as a function of Depth under 488 nm excitation

- Fluorescence spectra for different excitation depths.

- Shift of fluorescence maximum for various excitation depths

## Conclusions

- Both types of algae in the original concentration have strong absorption and cause spectral shift of fluorescence
- This spectral shift should be taken into account in the analysis of fluorescence and reflectance data for the waters with high chlorophyll (algae) concentrations

## Further Work

**After accounting for absorption and      attenuation we can graph pure fluorescence. **
**Compare pure fluorescence results from the experiment to the calculated ones using Matlab software**

## Acknowledgements

**Dr. Alex Gilerson**
**Professor Fred Moshary**
**NASA-NYCRI**