This duplicates a posting I made on the wsprnet.org website.

Aircraft reflection? Or something else? | WSPRnet
On Saturday, Jan 10th, I had my transmit-only beacon that I wrote sending both a visual MEPT indicator (the MV that you can see in the attached image) and the WSPR beacon, and tried out a simple program that simultaneously records, and later makes an FFT display of that portion of the band.

It seems to work!

I’m curious though about the brighter of the wspr messages visible here, which seems to have a shadow which arcs down to meet it. Is this the result of an aircraft reflection? There are some fairly close stations here (such as NN6RF) which conceivably could be reflecting off aircraft landing at Oakland airport, but I’m surprised that the signal level could be so high on the 30m band. I believe that such reflections can only occur if the source is reasonably close to the aircraft, correct?

I see a couple of other, similar traces in the 2 hour recording I did, which you can peruse here.