Digital elevation. I am using a different site now for DEMs. Will post it when I get home since Earth Explorer can be bit a of a pain forcing you to down load each DEM seperately. The good thing about it is that it has DTED1 .. the other site I use has DTED0 but the files are zipped into 3 - 4 files (used that site for the New Britain and New Guinea terrains in progress) instead of downloading about 100 DTED1s individually.