Head in the clouds

The traditional way to create clouds for a CG Earth is create a spherical shell slightly larger than the Earth itself, then mapping a cloud texture onto the transparency channel. As you an imagine, this technique works well for long shots in which the whole Earth is visible, but not so good for close ups and oblique camera angles:

Plain clouds texture mapped onto a flat, transparent layer

As always, adding a little procedural noise to a texture pattern can enhance the detail and quality of an image based texture:

Same flat cloud layer with noise patterns added

The final step would be to add displacement so that the clouds do not appear like a completely flat layer:

Add a little displacement into the mix to make things look more natural

This technique will hold for medium to long shot, but will completely fall apart if the camera gets too close.  Here are some more shots to test how far this technique can be pushed:

Glint in your eye

Viewed from space, the Earth generally does not appear very shiny, since most of the natural surfaces have low albedo and reflectance, with the exception of water. The ocean-covered parts of the Earth glint from fairly weakly to very strongly depending on various factors. However, even though 70% of the Earth's surface is covered with water. clouds also cover about 70% of the total land and water area. So the only time specular highlights are visible is when they peer through a cloudless sky, with still water (such as ponds and lakes) acting like polished mirrors giving off the strongest specular sun glints.

To recreate specular highlights on a CG Earth, a specular control map is needed. In addition, some noise should be added to simulate the ocean waves which breaks up the specular highlight into a glossy appearance from far.

The following are work-in-progress shots dated 27 Sept 2011:

The use of a specular map allows the rivers to glint in the Sun

Water is the most intensely specularly reflective material occuring naturally

The specular highlights for rivers and lakes are built into the land surface shader using a VEX network. As such, these bodies of water need to be depicted and aligned in the color, specular and displacement maps

Turbulent noise nodes are used to build the specularity of the ocean surface shader in a VEX network. A land/water mask is used to inform the shader where the ocean noise is needed