Why do the SID Data sunrise and sunset signatures have such a strange shape?
Don Rice at the Center for Atmopsheric & Space Science
at Utah State University has modeling software that shows
that the interference between two sine waves (one following the
ground and one reflected from the sky) gives a fairly good approximation
of the morning/evening signal changes for moderate distances.
The bigger question that they are looking at is "seeing" clouds of
gas (nitric oxide, NO) in the mesosphere/D-region based on the signals.
They are working with some observers on comparing the computer modeling
results with signal observations. It should work best for observers
< 2000 km from the transmitter but seeing what happens at longer
distances might be interesting too.
If you are interested in details about this research, you might try
contacting Don Rice at:
Center for Atmospheric and Space Science
Utah State University
4405 Old Main Hill
Logan UT 84322