Yes these are very good renderings... I really like the texture on the tank... really nice. I've looked at these and the grass threads trying to figure out displacement maps... completely new to me. I have in the past been able to use bump and normal maps to get really good water. I guess doing the same for the ground plane would be similar if you added another bump map layer to handle the smaller rougher details... hmmm... off to do some more testing.
I found this tute on Displacement maps... http://www.soylent-green.com/tutes/Displacement.html
Short quick and when I finished reading it, I knew I had to do a lot more research... http://www.land8lounge.com/profiles/blo ... tutorial-1
I found this - not exactly a tutorial but a good short visual description.