PhysicsFurther Testing/Validation

of the Satellite f/Q correctionKenneth J. Voss, Nordine Souaidia, and Albert Chapin

Department of Physics, Univ. of Miami

Andre Morel and David AntoineLaboratoire d’Oceanographie de Villefranche

Dennis Clark and Mike Ondrusek

NOAA/NESDIS

Thank NASA for their support(under our MODIS validation work)

PhysicsTest 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 Ed, a and bb.

Physics Previous experimental tests

• Morel, Voss, and Gentili, 1995 (JGR) used the first generation electro-optic RADS system. One Chl value (0.3 mg/m3) and o from 30-80o.

• Voss and Morel, 2005 (L&O) used the next generation RADS-II. Chl from 0.2 to 10 mg/m3, but o only from 30-40o deg.

• Both from cruises off of San Diego and into Gulf of California, rather restricted geographically.

Physics New data set uses NuRADS

Smaller systemOnly upwelling6 wavelengths2 minutes per

spectral setMuch better optical

characteristics

PhysicsMorel, 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 bb variation with Chl.

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

Physics 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.

PhysicsExample image and

reduced productAOPEX, 8/11/04, 521 nmo = 35o, Chl = 0.1 mg/m3

Average of 4 images (plus 2 Sides)

Lu=0.64 W/(cm2 sr nm)Qu = 3.72, u = 0.44

Physics

Important to understandthe effect of environmental

noise in the radiance distribution images

• Look at it from two viewsAverage Normalized St. Dev.

Physics Alternatively…

80

60

40

20

0

Frequency

of

Occ

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nce

(in

0.2

% b

ins)

1086420

Standard Deviation 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.

PhysicsExtent of Data Set Used

(in this study)

Physics Model-Data comparison

Error (data model) /N ,

Std (data model)2 /NDefine:

(Note: Chl= 0.11 mg/m3, 11o<o<40o)

Physics

Error vs Chl, each point is one day

Red dots, error; red bars, std; blue dots measurement std

Physics Error vs zenith angle

(only displaying 412 nm, others show nothing significant)

Physics 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/m3.• 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.)