Visually Accurate Multi-Field Weather VisualizationKirk Riley (Purdue)

David Ebert (Purdue)Charles Hansen (Utah)Jason Levit (Oklahoma)

Presented by,Arun Rao

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Domain

• Common weather Viz in global scale– Atmospheric interactions approx. in 2D– Storms and fronts that traverse globe

Image Courtesy of

NOAA

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Domain

• Example of 2D visualization

• Popular for showing particular, large area values

• Isosurfaces, vector fields

Image Courtesy of NOAA

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Domain

• Storm / Cloud scale– Equally important as global/synoptic

scale– Used for evaluation and prediction of

severe storms

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Domain

• 3D isosurfaces of storm data– Not very detailed– Interactions obscured

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Case Example

• Development of a Thunderstorm• Meteorologists trained via field

observations– “puffy” = convective– “wispy” = cirrus

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Realistic Viz applications• Look Pretty• Increase analysis & severe forecast

effectiveness • Train weather observers (e.g. tornado

chasers), students• Enhancements in:

– formulation– parameterizations – physics of numerical weather predecition

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Previous Work: Albedo “angle”• Albedo?• Blinn Model (1982)• Multiple Scattering

in Kajiya model (1984)

• All particles w/ homogeneous properties

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Multi-Field Data

• Volume w/ different types of particles• Hydrometeor particles

– Cloud– Ice– Rain– Snow– Graupel (soft hail)

• Hydrometeor Field = (mass hydro) / (mass air)

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Proposed System Flow• Look at particle

concentraion of a particle field

• Illumination is key for field seperation

• Cloud particles have high albedo– High albedo Lots of Scatter

Lots of Computation– Forward scattering

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Variables Ahoy!

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What is the proper rendering?

• Realistic visualization– Need cloud like color due to light – Need opacities based on particle type

• Step 1: Particle Field Concentration– Need Hydrometeor Field Mass Ratio

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Hydrometeor fields color map

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We have Concentration,…now what?

• L(w) is the final color of the pixel • T(s,w) = light attenuation between vector s &

w,• Bsca = scattering coefficient• P() = scattering phase function....• ( Omega ) viewpoint & angle of incidence.• L_bg = backround light intesity• L1( s, Omega) = light intensity at s in direction

Omega

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Attenuation T(s,w)

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Comparison of different Beta values

Improperly scaledHydrometeors

Vs.

Properly scaledHydrometeors

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Illumination Model L(s)

• Low Albedo shows clouds looking too dark

• Need to account for multiple scattering

• 90% of scattering is forward– Within 10 degrees

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3 categories of Light Scatter

• Unscattered– unimpeded

• Forward Scattered– Light that scattered, but going

forward

• Out Scattered– Light scattered anywhere else– Effectively extinguished

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Cone of Interest

• Define Arc with angle Theta

• Anything in arc forward scatter

• Per-pixel light buffer calculation

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Light contribution (Equation derived from Nishita

1996)• Unscattered• Center region forward scatter• Peripheral region forward scatter

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End Result (Transparency Illumination)

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End Result (Additional Detail)

• Portions of data User Adjustable• Noise functions

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End Result (frames per second)

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References• Paper• www.ecn.purdue.edu/purple/level2/

papers/vis03_riley.pdf• Albedo definition• http://zebu.uoregon.edu/~js/glossary/al

bedo.html• low albedo vs. high albedo• http://www.wordiq.com/cgi-bin/

knowledge/lookup.cgi?title=Albedo

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References• Attenuation• http://rkb.home.cern.ch/rkb

/PH14pp/node6.html#5• Extinction Coefficient• http://www.schorsch.com/kbase

/glossary/extinct_coeff.html• Scattering coefficient• http://www.atis.org/tg2k/_scattering_coe

fficient.html

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References

• optical depth• http://scienceworld.wolfram.com/

physics/OpticalDepth.html• Online Presentation• https://confex.webex.com/confex/

tool/docshow/playback.php?Rnd=153808716

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Images

• http://www.nnvl.noaa.gov/• http://www.ncdc.noaa.gov/oa/clima

te/onlineprod/drought/xmgr.html• http://danny.oz.au/travel/new-

zealand/p/1488-cloud-lake.jpg