A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tony Oz
Date: 2017 May 15, 10:04 -0700
This weekend was warm at Finnish Gulf with apparently normal atmospheric refraction conditions, I could see all the ususal distant beacons and islands. The conditions two weeks ago were very different - the distant shoreline was heavily distorted (what is usually a solid stretch of land going off beyond the horizon became a string of false islands), no beacons or an artillery fort 6 km away.
Yesterday I measured the angular height of the artillery fort 6 km away - 0°02' from water to the building top, 0°03' to the highest bush/tree top. Two weeks ago I could only see the tree top from the same spot on the shore (~2 meter above the water level).
Does this mean the negative refraction was approx. 3~4 arc-minutes? The image of the tree-top was floating in the air and was symmetrical: its' bottom part was a reflection of its' upper curve, just like through a cylindrical lense.
My impression is that one can detect such negative refration conditions by looking at the wave tops at the apparent horizon - they would be optically distorted rather than smooth.