3D Carbon Dioxide Visualization Appears in Prestigious Festival

July 31, 2017

A scientific visualization of 3D global carbon dioxide data computed at the NASA Center for Climate Simulation (NCCS) is appearing at this week’s SIGGRAPH 2017 Computer Animation Festival in Los Angeles, California. From hundreds of submissions the visualization is among only 25 videos selected for the prestigious Electronic Theater. The first screening is tonight at the Los Angeles Convention Center.  

“SIGGRAPH is one of the top venues for computer graphics in the world,” said Greg Shirah, lead visualizer on the project from NASA Goddard Space Flight Center’s Scientific Visualization Studio (SVS). The annual conference draws more than 14,000 attendees who line up early for seats at the Electronic Theater. Shirah and colleagues are thrilled that their work is the sole data visualization being shown on a massive screen alongside artistic videos and feature film special effects sequences. This honor by their computer graphics peers caps off a year that saw the visualization receive the Professional Winner award in Science Magazine's Data Stories contest.

“Seasonal Changes in Carbon Dioxide” belongs to a group of visualizations developed by the SVS in a collaboration with Goddard’s Global Modeling and Assimilation Office (GMAO).

“It is really exciting to see,” said Lesley Ott, GMAO carbon cycle scientist. “Some of this is science we have known for a long time, including that carbon dioxide can be carried by winds and transported over long distances. For the first time, we have satellite data, a model, and visualization come together to show that science to the public.”

The satellite data comes from NASA’s Orbiting Carbon Observatory-2 (OCO-2), built and operated by the Jet Propulsion Laboratory (JPL). OCO-2 takes more than 100,000 carbon dioxide observations daily. JPL processes the raw radiance data into a concentration product for researchers to use.

While providing a unique global perspective, OCO-2 concentration data shows only a top-down view of “how much carbon dioxide a column of air holds,” explained Brad Weir, a GMAO data assimilation expert affiliated with GESTAR/Universities Space Research Association. “We add the vertical information” by assimilating the OCO-2 data into the Goddard Earth Observing System (GEOS) computer model of the atmosphere.

The GEOS modeling suite includes a constituent data assimilation system designed for ingesting carbon and aerosol observations. As in its weather forecasting research, the GMAO assimilates the OCO-2 data, runs the model forward until the next assimilation point, assimilates data again, and so on. This study repeated those steps for September 2014 to September 2015—capturing a 3D documentary of the ebbs and flows of carbon dioxide over a full year.

The model run consumed 336 cores of the NCCS Discover supercomputer for 22 days. Weir set GEOS to use grid boxes 50 kilometers wide throughout the atmosphere. Running GEOS at that resolution, combined with the OCO-2 observations, yielded about 1 terabyte of total output.

In translating such data into compelling visualizations, the SVS uses several of the same software tools as feature film special effects companies. Central to the carbon dioxide project was Pixar RenderMan, the leading tool for a 3D computer graphics technique called volume rendering. “You are creating little volumes in space and assigning them an optical density and color,” said SVS director Horace Mitchell, who collaborated with Shirah on the visualization. “RenderMan requires that those volumes be uniform rectangular volumes, but the GEOS model is not structured that way.”

While the horizontal grid is fixed, the model’s vertical levels depend on atmospheric pressure and their height can vary both by location and over time. For RenderMan, Mitchell had to reformat the GEOS vertical levels into equal-height columns of stacked grid boxes also of equal height. “It was a completely different geometry,” he said.

To make carbon dioxide’s global movements understandable to a lay audience, Shirah and Mitchell first tested using a flat-map projection of the Earth. The results had too much distortion, especially at the poles. So, they decided to use the oval-shaped Mollweide projection, where each area on the map is the same size horizontally and vertically.

After regridding the data into the Mollweide projection, the visualizers created intermediate files for RenderMan. “This is the first time that we used Pixar’s new RIS renderer, and it worked very well,” Shirah noted. RIS is a major departure from Pixar’s previous renderer and uses a different data format. Shirah attributes having the first version of the visualization ready for Fall 2016 conferences to Pixar’s willingness to send two staff members to Goddard for a week to help the SVS with adopting RIS.

In doing the volume rendering, the visualizers spent a lot of time deciding what viewers get to see and do not get to see. “Every box has data. If you showed everything, all you would see is a solid brick," Shirah said. With guidance from the GMAO scientists, Shirah and Mitchell picked a color range from blue (low) to red (high), corresponding to a range of 390 to 508 parts per million of carbon dioxide. The goal was to show only high and low values, so they also used transparency with some of the middle-range colors. Vertical exaggeration brings out the 3D structure of the colored carbon dioxide plumes and highlights how surface topography influences airflow.

The 80-second visualization being shown at SIGGRAPH focuses on March 1 to July 31, 2015 to tell the story of how carbon dioxide builds in winter and gets drawn down by photosynthesis in spring and summer. Enhancements to this version include narration, data source and vertical exaggeration labels, a flat map that grows vertically to highlight the exaggeration, and a pull-out of the March 1 view beneath the July 31 view at the end “that really drives home the differences,” Shirah said.

Beyond SIGGRAPH, the 3D carbon dioxide visualizations have appeared in numerous presentations, from Goddard seminars to science conferences and public events worldwide. They have been effective in communicating to diverse audiences. Even scientists marvel at seeing this data as never before. As Weir noted, “Instrument people who do measurements in the upper atmosphere say, ‘we were observing things like that, but we were not sure they were real.’” Ott was excited to watch South American fire pollution get blown against the mountains and change direction. “This visualization has been a revelation to people who work with this data every day,” she said.

“Seasonal Changes in Carbon Dioxide” is the third SVS visualization selected for the SIGGRAPH Electronic Theater. Additional contributors include Steve Pawson from the GMAO; Leann Estrada, Ian Jones, and Laurence Shuler from the SVS; Annmarie Eldering from JPL/OCO-2; Heather Hanson from the NASA Science Communications Support Office; and Joy Ng and Stuart Snodgrass from Goddard TV.

Jarrett Cohen, NASA Goddard Space Flight Center

More Information
Seasonal Changes in Carbon Dioxide

SIGGRAPH 2017 Electronic Theater and VR Theater Listings

Science 2017 Data Stories Winners