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Absorption properties of marine particles and CDOM:

Absorption properties of marine particles and CDOM:. Use of special measurement devices: Ultrapath and PSICAM Marcel Babin Annick Bricaud Edouard Leymarie Antoine Sciandra. Motivations (1).

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Absorption properties of marine particles and CDOM:

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  1. Absorption properties of marine particles and CDOM: Use of special measurement devices: Ultrapath and PSICAM Marcel Babin Annick Bricaud Edouard Leymarie Antoine Sciandra

  2. Motivations (1) - The relative contributions of CDOM, phytoplankton and non-algal particles (NAP) to light absorptionhave to be known for predicting/interpreting the inherent and apparent optical properties of the ocean. - In open ocean waters, especially in ultra-clear waters, these relative contributions are difficult to quantifyand poorly known. We believe that these relative contributions are highly variable.

  3. Motivations (2) - Some of our previous observations (aNAP/ap is largest in the Med Sea, and lowest in the Pacific, Bricaud et al. 1998) suggest that iron could contribute to non-algal absorption in some open ocean waters - Iron could also play a role in light absorption by CDOM (e.g. Emmenegger et al. 2001)

  4. Objectives for the BIOSOPE cruise - To quantify the relative contributions of phytoplankton, CDOM and NAP to light absorption in the BIOSOPE area, using new (highly sensitive) measurement devices • - To study the variability of these contributions in the various areas explored during the cruise (contrasted wrt. iron limitation) • -> role of iron in light absorption by NAP and CDOM? - To extend our database of phytoplanktonic absorption to ultra-oligotrophic waters, and check the validity of the previously developed parameterizations (af(l) vs. chl)

  5. Methods - Classical methods: • Particulate absorption: concentration of particles on a GF/F filter, spectrophotometric analysis • CDOM absorption: spectrophotometric measurements using 10 cm cells These methods are adequate for mesotrophic waters (will be used as often as possible as reference) but not for ultra-oligotrophic waters (CDOM absorption too low; large seawater volume needed for particulate absorption) • two alternative (complementary) methods: • - Ultrapath (commercial instrument, pathlength 2 m) • - PSICAM (prototype in development, pathlength > 5 m)

  6. Ultrapath system 2cm 10cm 200cm 50cm Ultrapath cell Peristaltic pump Spectrophotometer TIDAS 1 Light source Optical fiber Ultrapath cell Sample

  7. Ultrapath: tests on natural samples and algal cultures(DEA Maria Vlachou, 2003) Phytoplanktonic culture Dyfamed, 40 m • Sensitive method for CDOM absorption measurements • Can be used also for particulate absorption measurements (needs accurate scattering correction –> ac-9) • The rinsing protocol is being automatized to provide reproducible measurements (A. Sciandra, G. Malara)

  8. Spectralon sphere Water sample Monochromatic light source Detector Inlet and outlet Methodological Development: PSICAM (Point Source Integrating Cavity Absorption Meter) • Theoretical concept formulated by Elterman (1970), developed by Kirk (1995) • Advantages : • Extremely sensitive (pathlengths up to more than 10 meters) • Insensitive to scattering by particles

  9. Agenda of the PSICAM development • Dec 2003 – Feb 2004 : Development of a 3-D Monte Carlo code to optimize the design of the sphere • Feb 2004 : Visit to JTO Kirk’s lab • March-April : Building of the system • May-June : Tests in lab and calibration protocol • July-October : Tests at sea •  BIOSOPE

  10. Supplementary measurements needed • HPLC pigment concentrations • In situ absorption/ attenuation (ac-9) measurements (correction of Ultrapath ap measurements) • Particle dry weight (filtration of 7 L of seawater) • Iron concentration (particulate and dissolved), and ionic (ferric/ferrous) composition if possible

  11. Spectralon sphere Water sample Monochromatic light source Detector Inlet and outlet Methodological Development: PSICAM (Point Source Integrating Cavity Absorption Meter) • Theoretical concept formulated by Elterman (1970), developed by Kirk (1995) • Advantages : • Extremely sensitive (pathlengths up to more than 10 meters) • Insensitive to scattering by particles

  12. Graph window to plot results in real time Simulation window to follow the calculation 2D picture to display current device projection. shell window to program different tasks SimulOForward 3-D Monte-Carlo Simulation Program

  13. PhotonSource n=1 n=1.7 Parallel plate • Various surface properties can be selected : • Lambertian surface : • (example : diffusion of a parallel beam) • Reflection - Absorption : Photon Source Absorption Reflection • Various Volume properties can be selected : • Transparent, Absorption • Diffusion with different choices of phase function Surface / Volume properties • Snell – Fresnel Laws : (example : parallel plate)

  14. Simulation of the Point Source • Water sample : a = 5 m-1 , b = 2 m-1 (Petzold) • Ideal and Simulated Sources (Number of photons : 3.5 108)  99 % Lambertian surface

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