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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
ura
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.)