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Visually Accurate Multi-Field Weather VisualizationKirk Riley (Purdue)
David Ebert (Purdue)Charles Hansen (Utah)Jason Levit (Oklahoma)
Presented by,Arun Rao
Arun Rao 3/2/04
Domain
• Common weather Viz in global scale– Atmospheric interactions approx. in 2D– Storms and fronts that traverse globe
Image Courtesy of
NOAA
Arun Rao 3/2/04
Domain
• Example of 2D visualization
• Popular for showing particular, large area values
• Isosurfaces, vector fields
Image Courtesy of NOAA
Arun Rao 3/2/04
Domain
• Storm / Cloud scale– Equally important as global/synoptic
scale– Used for evaluation and prediction of
severe storms
Arun Rao 3/2/04
Case Example
• Development of a Thunderstorm• Meteorologists trained via field
observations– “puffy” = convective– “wispy” = cirrus
Arun Rao 3/2/04
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
Arun Rao 3/2/04
Previous Work: Albedo “angle”• Albedo?• Blinn Model (1982)• Multiple Scattering
in Kajiya model (1984)
• All particles w/ homogeneous properties
Arun Rao 3/2/04
Multi-Field Data
• Volume w/ different types of particles• Hydrometeor particles
– Cloud– Ice– Rain– Snow– Graupel (soft hail)
• Hydrometeor Field = (mass hydro) / (mass air)
Arun Rao 3/2/04
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
Arun Rao 3/2/04
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
Arun Rao 3/2/04
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
Arun Rao 3/2/04
Comparison of different Beta values
Improperly scaledHydrometeors
Vs.
Properly scaledHydrometeors
Arun Rao 3/2/04
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
Arun Rao 3/2/04
3 categories of Light Scatter
• Unscattered– unimpeded
• Forward Scattered– Light that scattered, but going
forward
• Out Scattered– Light scattered anywhere else– Effectively extinguished
Arun Rao 3/2/04
Cone of Interest
• Define Arc with angle Theta
• Anything in arc forward scatter
• Per-pixel light buffer calculation
Arun Rao 3/2/04
Light contribution (Equation derived from Nishita
1996)• Unscattered• Center region forward scatter• Peripheral region forward scatter
Arun Rao 3/2/04
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
Arun Rao 3/2/04
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
Arun Rao 3/2/04
References
• optical depth• http://scienceworld.wolfram.com/
physics/OpticalDepth.html• Online Presentation• https://confex.webex.com/confex/
tool/docshow/playback.php?Rnd=153808716