Southern Ocean Sea level to Mountains at 300 miles
"There is almost no dust or solid particles in the Antarctic air and the prevailing winds blowing off the continent have small moisture content. Consequently, the visibility is usually very good and often exceptional, a fact which, if not appreciated, may lead the observer into serious error when judging distances. An object which may be thought to be but 5 miles distant could well be 30 miles away, and mountains have been sighted at 300 miles."
- PUB. 200 (PLANNING GUIDE SAILING DIRECTIONS & ENROUTE) ANTARCTICA 2005 NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY http://wiki.247flatearth.net/images/3/3f/Pub200bk2005.pdf