Observing the Earth from space

As mentioned in a recent post, the Earth's atmosphere makes everything appear bluish from space. To obtain rich, colorful satellite imagery in which the ground vegetation appears naturally green, color correction must be done to remove the bluish tint. There is a nice tutorial from NASA on how to do that here.

Because I'm using BMNG imagery for my base texture, the source data has already gone through such color correction process by NASA personnel. My work would be to reverse the process by adding an atmosphere on top and therefore re-introducing a bluish tint.

I have a difficult time deciding how much "atmospheric blue" is enough to make the renders look realistic and still naturally colorful. I do have a dial for the amount of atmospheric density, but it seems that there is no single setting that will work with all viewing distances and angles. More research needed in this area... :/

Meanwhile, here's another work-in-progress shot (dated 28 Sept 2011) compared with a still frame from a NASA video filmed from the ISS. The texture is satellite imagery from BMNG January 2004, and we are looking south down at the Rocky Mountains on the North American continent, with the Pacific Ocean to the right:

Under the sea (random WIP shots)

Apart from the mountains rising up, I also used the Blue Marble's bathymetry data to create the ocean floor using displacement mapping. The sea floor coloring is based purely on guesswork, with cyan for shallows and dark blue for deeper depths. Thankfully once the ocean water goes on top, the sea bed is practically invisible. I kind of like the colorful look though.

(All work-in-progress images below are dated 27 Sept 2011):

Displacement mapped terrain means the mountains will rise up and cast shadows

Displacement mapped seabed using bathymetry data means the ocean floor really sinks below sea level

"Australia, Australia, this is you" ^^ (The sea layer covers up all traces of the ocean floor)

Shallows off the west coast of Central Africa (and an early attempt at specular highlights for the ocean)

Anyway, displacement mapping is cool but it really slows down the rendering a LOT. And I'm using it everywhere ^_^;;

Behold our mothership

Artists like to depict the Earth as a deep blue planet with richly saturated green or brown continents. From a low orbit, the Earth indeed looks rich and colorful. But from the edge of space onwards, a layer of blue covers the entire planet, desaturated in a manner artists understand as atmospheric perspective.

The air molecules and aerosols in the Earth's atmosphere scatters light of different wavelengths by different amounts. Light with shorter wavelengths (blue end of visible spectrum) gets scattered more than light with longer wavelengths (red), this being the simplified explanation for why the sky is blue.

NASA's Blue Marble 2002. Colorful and beautiful, but not quite what the astronauts saw...?

The most famous photo of the Earth, taken on Dec 7, 1972 by the crew of Apollo 17

Furthermore, most of the ground terrain (especially vegetation) has low albedo which means only a very low percentage of sunlight gets reflected back into space. The oceans would appear black if not for the fact that the water reflects the blue sky. The low albedo of soil and plant life is also the reason why vegetated areas appear very dark from space, and not the bright, beautiful green that we see in the atlas.

Incidentally, the polar ice (being of high albedo) is mostly responsible for reflecting sunlight away from the Earth and reducing global warming by the Sun. But the Arctic ice and Antarctic ice shelves have been melting steadily in recent years, a matter of some concern for environmentalists.

Real photography of the Earth from deep space are few and far between. From them, we can observe that the brightest things visible, along with the blue scattered atmosphere, would be clouds and snow, followed by ice and sand. The "true" colors are not as cheerful as we might like, but we can always take artistic license and put some more hues back into our CG Earth render ^_^


Some of my more presentable rendering attempts (dated 13 Sept 2011, rendered using Houdini) follows:

Naturally, city lights will not appear so bright without either nigh-vision goggles or long exposures, and would be practically impossible in reality, but this kind of "day and night" artistic treatment is always popular ^_^

After rounds of tweaking, I keep coming back to this particular palette, though realistically I should use a deeper shade of blue. For now, this would be the overall look and feel until I come up with something else later...

The air we breathe

One of the earliest goals I set out since the beginning was to have an atmosphere that is not simply a thin shell layer. It's an old trick, but by using multiple layers of closely packed concentric spheres and mapping opacity data onto each layer, a spatial sampling can be achieved which will allow the air to have apparent volumetric density.

Here are some early test shots (dated 3 Sept 2011). Imagine the spikes as mountainous terrain and the dense air forming clouds which gather at lower altitude:

While this technique has its value, it's a case of looking nice from afar, but being far from nice close up

Eventually, I moved on to another alternative method for rendering volumetric clouds, but until this day still have not found a satisfactory solution to create properly nice clouds for this project. More R&D ahead... ^^;;

Early screenshots of rebooted version

As mentioned before, I started from scratch after a year and the new version is being created using Side Effect's Houdini. I'm using the free Apprentice version at home so the renders are limited in resolution and there is a huge watermark on the bottom right corner:

Shadowed side of clouds and terrain are always too dark

Terminator red zone too wide and unnatural looking

 

Landmasses too dark, sun glint is too broad

Images are dated 30 Aug 2011. Still a long way to go at this juncture...

A faltering start...

Armed with some research and basic concepts, I set about creating the actual Earth model. Modeling wasn't an issue at all, since all the layers (land, clouds, atmosphere) were made up of only spheres.Texturing, lighting and rendering proved to be fraught with challenging technical difficulties, some of which were mentioned before in a previous post.

My original approach was to render different layers and passes in Maya and then composite, color correct and add effects in After Effects. From June 2010 to August 2011, I tried this approach (with about half a year of lull in between) and after literally hundreds of attempts, completely failed to get the desired look.

In August 2011, I re-attacked the project with a vengeance, working intensely for long hours after work and during weekends. Ultimately I realized that my initial objectives could not be achieved using this technique alone. While some of the output feels quite nice and artistic to me, none of them look natural or sufficiently realistic :(

Some sample renders:

 It was at this point that I decided to change approach completely...

Visions of fact or fiction?

The Earth also features in a lot of movies, art and games. In these products the visuals are designed to look believable, or just plain cool. It should be safe to assume that the artists have taken their inspiration and reference from actual satellite imagery. But do they capture what an astronaut actually sees when he or she looks out the window of the Space Shuttle or takes a space walk outside the ISS?

Autobots descend onto Earth in Transformers (2007)

Nuclear missile launch seen from space in Call of Duty: Modern Warefare 2 (2009)

Commander Shepard watches the Earth burn in the Mass Effect 3 debut trailer

So, how should my photorealistic CG Earth look? A good area worth investigating indeed! ^^