Further Testing/Validation

Physics

of the Satellite f/Q correction

Kenneth J. Voss, Nordine Souaidia, and Albert Chapin Department of Physics, Univ. of Miami Andre Morel and David Antoine Laboratoire d’Oceanographie de Villefranche Dennis Clark and Mike Ondrusek NOAA/NESDIS Thank NASA for their support (under our MODIS validation work)

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Test of Q(  o ,  ,  ) portion of Morel, Antoine, Gentili (2002) f/Q algorithm • Tests Q through the measurement of the upwelling radiance distribution, as: Q (  o ,  ,  ) = Eu/L(  o ,  ,  ) • A single measurement of the upwelling spectral radiance distribution gives Eu [through integration of Lu (  o ,  ,  ) ] and L (  o ,  ,  ), with the same instrument, so is an accurate method to get Q (  o ,  ,  ).

Note that f is not available, as it requires simultaneous measurement of E d , a and b b .

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Previous experimental tests • Morel, Voss, and Gentili, 1995 (JGR) used the first generation electro-optic RADS system. One Chl value (0.3 mg/m 3 ) and  o from 30-80 o .

• Voss and Morel, 2005 (L&O) used the next generation RADS-II. Chl from 0.2 to 10 mg/m 3 , but  o only from 30-40 o deg. • Both from cruises off of San Diego and into Gulf of California, rather restricted geographically.

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New data set uses NuRADS Smaller system Only upwelling 6 wavelengths 2 minutes per spectral set Much better optical characteristics

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Morel, Antoine and Gentili (2002) model features • Index is Chl,  o ,  v , and  – Important that Chl is just a convenient index into the tables…could do something else, but this works.

• Includes Raman scattering (inelastic process).

• Radiance distribution depends critically on the phase function.

– Includes a phase function which varies with Chl, not just a single particle phase function to match observed b b variation with Chl.

– Calculation uses spheroids, and not spheres (which can be anomalous in the backscattering direction.

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Data reduction • Process radiance distribution images according to Voss and Zibordi (1989).

– Immersion test critical in underwater measurement, with curved windows not straight forward.

• Additional steps to locate geometry required.

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Example image and reduced product AOPEX, 8/11/04, 521 nm  o = 35 o , Chl = 0.1 mg/m 3 Average of 4 images (plus 2 Sides) L u =0.64  W/(cm 2 sr nm) Q u = 3.72,  u = 0.44

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Important to understand the effect of environmental noise in the radiance distribution images • Look at it from two views Average Normalized St. Dev.

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Alternatively… 80 60 40 20 0 0 2 8 10 4 6 Standard Deviati on in % % Std. Dev. Histogram. Illustrates that it is unlikely that Std Dev. of pixel matchups with a model will be better than 3% or so…..radiance distribution just isn’t that stable.

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Extent of Data Set Used (in this study)

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Model-Data comparison Define:

Error

  (

data



model

) /

N

,

Std

  (

data



model

) 2 /

N

(Note: Chl= 0.11 mg/m 3 , 11 o <  o <40 o ) 

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Error vs Chl, each point is one day Red dots, error; red bars, std; blue dots measurement std

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Error vs zenith angle (only displaying 412 nm, others show nothing significant)

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Conclusions • To date, within the accuracy/environmental noise of data, Morel et al. 2002 model works.

• Need more data in Chl range from 0.4 to 10 mg/m 3 .

• Need another alternative in Case II waters, have more turbid data sets to look at this problem.

• Polarization? Have modified NuRADS to provide upwelling polarization data (see poster by Souidia et al.)