Have this as well..put my own map in and its like a diffused haze that moves with the modulation of the grass..it covers the whole terrain..I initially made my map in Doom studio and it didn't have this problem I imagine the settings are a little jacked in Eclipse..
http://i1212.photobucket.com/albums/..._10_58_418.jpg
http://i1212.photobucket.com/albums/..._13_57_975.jpg