EDIT: The stories in Phys.org NASA's EPIC view spots flashes on Earth and Live Science Mysterious Light Flashes 1st Spotted by Carl Sagan Explained seems to have information potentially relevant to this. Apparently these have been seen for decades by several different spacecraft.
Journal Article now viewable as epdf: http://onlinelibrary.wiley.com/doi/10.1002/2017GL073248/epdf
Watch the NASA Goddard video EPIC Observations of Ice in Earth's Atmosphere:
This answer has been bugging me for a while, so I would like to challenge it by asking for a technical reference, journal article, or something that explains the phenomenon more fully.
This purple dot appeared around the sub-solar point in an EPIC photo of the Earth, from the DSCOVR satellite in a Lissajou orbit around the Sun-Earth L1 point.
Is the purple dot really caused by an effect of Cassegrain optics and/or coherent backscattering? If so, can I read further on the technical explanation of small, highly collimated bright spots at sub-solar points on Earth seen from space?
Note, this looks to be of the order of 10km or less at a distance of 1,500,000km! That's what I mean by highly collimated!
Note also that it is of the order of 1 pixel of the EPIC's camera as well.
above: Bright spot at sub-solar point taken from this question.
above: Screen capture from Google maps, annotated with a box marking the approximate location and size of the cropped image with the purple dot.
above: The full DSCOVR EPIC image taken from this question. If you right click and open in a separate view, and zoom, you can see the purple spot.
Bright, highly collimated reflections could be produced by highly reflective, fairly flat surfaces, and water is one such example.
Watching this video one can clearly see occasional bright flaring near the sub-solar point when it is on water, presumably the water is unusually calm and a much larger fraction of sunlight is directed into a cone around normal incidence.
above: Screen shot from DSCOVR video showing an example of a common bright reflection from calm seas near the sub-solar point.