Cover stories: Making the Orbiting Carbon Observatory-2 cover

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Science  13 Oct 2017:
Vol. 358, Issue 6360, eaaq1546
DOI: 10.1126/science.aaq1546

Cover stories offer a look at the process behind the art on the cover: who made it, how it got made, and why.

The 13 October 2017 cover (Fig. 1) highlights a package of papers presenting data from NASA’s half-ton Orbiting Carbon Observatory-2 (OCO-2). The cover image depicts atmospheric CO2 concentrations and global distribution data as obtained by OCO-2, which revolves around Earth at an altitude of 705 km.

Atmospheric CO2 is a greenhouse gas that maintains heat near Earth’s surface. Scientists largely agree that the additional CO2 that has been introduced into the atmosphere since the start of the Industrial Revolution has increased Earth’s mean temperature, a pattern that will continue over the coming years. Studying the way CO2 interacts with the atmosphere and natural carbon sinks is key to understanding our impact on the planet’s climate.

Fig. 2

CO2 data from the OCO-2 observatory collected during July 2015.

Credit: NASA Scientific Visualization Studio

The OCO-2 observatory is unique in that it does not record CO2 levels directly by measuring from the air column; rather, it logs how much sunlight is reflected off of CO2 molecules within the atmosphere. These data are analyzed and visualized as a colored gradient (Fig. 2) that illustrates the relative concentrations of CO2 between 390 and 405 parts per million. Captured at set intervals during 2014–2016, the collected data can be animated (Movie 1) to show the movement and concentrations of CO2 around the globe. The movie is, in essence, a clearer vision of the data shown on the cover because it allows us to observe real CO2 levels as they fluctuate over time.

Movie 1 OCO-2 data animation

OCO-2 data collected at set intervals during 2014–2016, animated to show movement and concentration of CO2. The colored gradient reflects the relative concentrations of CO2 between 390 and 405 parts per million.

Credit: C. Bickel/Science; NASA Scientific Visualization Studio

For this cover, I wanted to show the entire globe layered with the OCO-2 data but also ensure that the illustration was engaging, beautiful, and not overly similar to standard Earth visualizations. I choose a still image from data collected in July 2015 and converted it to a texture map that was imported into MAXON’s Cinema 4D, our 3D design software package. This map was projected onto a sphere outside the rest of the Earth model (Fig. 3). To finalize the model, I textured and layered a number of other spheres of varying radii to create Earth’s surface, clouds, and atmosphere.

Fig. 3

Illustrating the layered nature of the Earth model. Four concentric spheres of differing radii made up the composite of multiple textures that led to the final rendered Earth image.

Credit: C. Bickel/Science

I soon encountered a problem: How would the multiple stacked spheres interact within the 3D render engine? After reviewing many test renders, I noticed unappealing visual effects starting to develop around the edges of the Earth model, at roughly 90° to the camera. This was a consequence of the layered model and how the texture maps and transparency settings essentially overlapped and tightened up near the far edges of the globe (Fig. 4).

Fig. 4

With the rendering camera facing a sphere within the 3D work space, the far edges of the Earth model experience distortion and a visually confused edge with a harsh border. Correct application of transparency helps to control the final output, shown here with a soft natural edge.

Credit: C. Bickel/Science

The answer was to selectively and deliberately apply alpha channels (black and white images used to control transparency) to each of the spheres in the layered model. These alpha channels were used to blur the edges of each sphere in differing ways so that the render engine would blend between the texture effects (Fig. 4) and soften the globe overall.

I chose a view of Earth that would be recognizable geographically while accurately depicting OCO-2 data that illustrates high levels of CO2 over developing nations. After layering the data aligned with the 180th meridian to ensure accurate placement, I tweaked the translucency of the texturing to find the right balance between illustrating the data and visualizing Earth itself.

The final result is a unique and visually appealing illustration of Earth that showcases data from OCO-2, a mission that will hopefully lead to a better understanding of our impact on the atmosphere and the planet at large.

Chris Bickel, Senior Scientific Illustrator at Science

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