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ESA Frascati 31 Oct 2014 [email protected] 1
Determination of the light availability in ocean water utilizing
Vibrational Raman Scattering
Tilman DinterV. Rozanov, J.P. Burrows, Astrid Bracher
ESA Frascati 31st Oct 2014
Phytooptics Group
Dinter et al. submitted
ESA Frascati 31 Oct 2014 [email protected] 2
Light availability
Sunlight is the main driver of biological and physical processes in ocean water.
Quantify processes of photosynthesis, biomass and primary production.
For calculations of heat transfer and fluxes. → climate modeling
ESA Frascati 31 Oct 2014 [email protected] 3
Definition of light availability or Depth Integrated Scalar Irradiance (DISI)
Radiation energy density:
Actinic flux or scalar irradiance:
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Defined as number of photons in the water column. Directly correlated to strength of Vibrational Raman
Scattering (VRS). Depends on solar zenith angle (sza), surface,
atmosphere and the absorption and scattering of water body.
Definition of light availability or Depth Integrated Scalar Irradiance (DISI)
ESA Frascati 31 Oct 2014 [email protected] 5
Vibrational Raman Scattering in liquid water
What is Vibrational RAMAN Scattering in liquid water?
• VRS is an inelastic scattering effect• Incoming light excites water molecules to
vibrations• Reemission in the same wavelength
(RAYLEIGH scattering)• Reemission in other wavelength (RAMAN
scattering)
FIZ, Berlin (http://vs-c.de)
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Vibrational Raman Scattering in liquid water
• Transspectral processes causes filling in of absorption or FRAUNHOFER-lines
• More photons are shifted into than out of the lines• I-: original ; I+: after filling in process• Defining pseudo-absorber like in DOAS-method after BEER-
LAMBERT-Law
ESA Frascati 31 Oct 2014 [email protected] 7
Vibrational Raman Scattering in liquid waterModeled with SCIATRAN
• Transspectral processes causes filling in of absorption or FRAUNHOFER-lines
• More photons are shifted into than out of the lines• I-: original ; I+: after filling in process• Defining pseudo-absorber like in DOAS-method after BEER-
LAMBERT-Law
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Vibrational Raman Scattering in liquid water
Excitation at 390-444.5nm
Reemission at 450-524nm
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Model Scenario SCIATRAN (Rozanov et al. 2014)
Clear Rayleigh, Ozone Atmosphere Reference solar zenith angle 40° Ocean:
500m homogeneous mixed water body, black albedo Surface: Cox & Munk (1954) approx. (wind speed 4.1 m/s) Standard chl-a CASE-I water model (Morel et al. (1991) and
Prieur & Sathyendranath (1981)) for absorption Molecular (Rayleigh) scattering by Buiteveld et al. (1994) Particle scattering based on bi-modal distribution model of
Kopelevich (1983) Conc. of small and large particles are determined by one
parameter model of Haltrin (1999)
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VRS Weighting Function from TOA radiance simulations
C = 0.1 mg/m^3
C+ΔC = 0.11 mg/m^3
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Weighting Function Differential Optical Absorption Spectroscopy (WF-DOAS)
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VRS-WF Ocean IOPswithout VRS
Atmosphere Polynom
Weighting Function Differential Optical Absorption Spectroscopy (WF-DOAS)
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VRS-WF Ocean IOPswithout VRS
Atmosphere Polynom
Weighting Function Differential Optical Absorption Spectroscopy (WF-DOAS)
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Modeling subsurface radiation to determine light availability (DISI)
- Integrated over VRS excitation (390 – 444.5nm)
- Reference solar zenith angle 40°
- The less chl-a the more light is available in the ocean water
ESA Frascati 31 Oct 2014 [email protected] 15
- Integrated over VRS excitation (390 – 444.5nm)
- Reference solar zenith angle 40°
- The less chl-a the more light is available in the ocean water
Modeling subsurface radiation to determine DISI: Change with chl-a conc.
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Modeled relationship between DISI and VRS fitfactor
+
=>
Fitfactor (strength) of
VRS signal has a
nearly linear
relationship to DISI
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Simulating effects of different absorptions and profiles
Different specific absorption spectra Different profiles (Uitz et al.)
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Simulating effects of different absorptions and profiles
+
=>Leads to a maximum
error of ~10%
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[phot/sec/m]
SCIAMACHY DISI from VRS WF-DOAS fit (sza corr)
ESA Frascati 31 Oct 2014 [email protected] 23
Summary and Outlook
A new method is introduced to determine the light availability from VRS effect
Has the potential to determine PAR directly (without former determination of a, b, and PAR(0+))
Applicable to other hyperspectral sensors like GOME-2, OMI, or upcoming TROPOMI with different overpass times (-> daily cycle)
Publication submitted at OS
ESA Frascati 31 Oct 2014 [email protected] 25
Appendix
Modeling subsurface radiation to determine DISI
Comparison
Comparison
