Wave refraction, optical illusions, and the Titanic

One thing I like about physics is how the same math and physics principles can be used to understand a variety of different phenomena. In a recent post I briefly reviewed the use of refraction and reflection of seismic waves for learning about the layering of the sea floor. Other types of waves that can be refracted and reflected include sound waves, light (waves in the visible part of the electromagnetic spectrum), and other types of electromagnetic waves.

I came across two interesting articles in the last few days about wave phenomena that I wanted to mention. So let's call today's post just a little bit of (geo)physics, maybe because I am too lazy to dig into the next IGY Bulletin article.

The first article appeared Tuesday in The Guardian, one of three newspapers I look at every day and financially support. (The other two are the New York Times and the local Lancaster LNP.) The article was about a mysterious "iceberg" that appeared off the coast of Vancouver Island, a sighting that was surprising because it had not been otherwise noticed.

Simone Engels’s photograph of the apparent iceberg off the coast of Vancouver Island (The Guardian, 25 Jan. 2022)

The photographer Simone Engels was actually seeing the Cheam mountain range on the mainland of British Columbia, nearly 125 miles away, and below the horizon from where she was standing. This optical illusion was caused by what is known as a “superior mirage” which can occur when there is an atmospheric temperature inversion with a band of warm air resting on a layer of cold air. In such a situation, light rays from the source object are refracted (bent), projecting an image into the "wrong" position. The temperature boundary of the inversion represents a discontinuity in terms of light velocity, so the light waves are bent and seen to be at ground level even though the object actually lies below the horizon. 

Superior mirage of the "phantom iceberg" (The Weather Network)

The Italian term for such a superior mirage is Fata Morgana, and this video also explains and shows how it works:

This is the opposite of an "inferior mirage." For example, when you drive on a hot day and see mirage “puddles” on the pavement, that’s basically a repeated image of the sky that’s bent into a visible spot on the ground.

An article in the Smithsonian Magazine from 2012 that I came across described the hypothesis that a superior mirage led to the sinking of the Titanic in 1912 and the more than 1500 deaths that resulted. According to this idea, a thermal inversion and corresponding optical distortion camouflaged the presence of the looming iceberg to those on the Titanic until it was too late, and then distorted the distress signals that the Titanic sent out to the nearby freighter Californian after it was hit.

As for a stamp that shows seismic reflection and refraction, the former German Democratic Republic (aka GDR, East Germany, or Deutsche Demokratische Republik -- DDR -- auf Deutsch) issued a set of four geophysics stamps in 1980. These stamps are what philatelists call "se-tenant": two or more stamps of different colors, designs or values that are printed adjacent to each other on one sheet. (The American and Swedish sets on stamp collecting showed in my recent posts were also se-tenant.) The German 35-pfennig (pre-Euro) stamp (Scott #2145) shows seismic waves that are both reflected and refracted by layers in the geologic subsurface, used for reconnaissance exploration of oil and natural gas deposits.

Cover from my collection showing GDR Scott block #2146a, including stamps #2143-2146, on the topic of geophysical exploration