Mary Shafer wrote:
I hate to tell you this, but 20,000 ft isn't "low level". Low level
is a couple of hundred feet off the deck. I suppose you could stretch
it to 10,000 ft or so, but the SR is still subsonic at that altitude.

?????

Mary, given your past association with the Blackbird, I am perplexed
that you choose to castigate my use of the English language rather than
give us the benefit of your experience: the site I gave a link to says
that the information is unclassified, and I had hoped that you could at
least confirm that it was broadly correct. I can only read your
response as telling me that I should have written "/relatively/ low level".

Looking at the graph I linked to should make it clear that my whole
point was that the SR-71 was subsonic at levels low enough to be seen
and photographed from ground level, and indeed all the way up to 20,000
feet or so.

I would say that you can't call it "low flying" until one or more of the
crew, ground observers or wingmen are scared My father-in-law ended
up as a specialist Navigator on Canberra PR9's after a career which
included Vulcans and Phantoms; he reckoned you weren't into "low flying"
until you got down to 50 feet.

To get back to the original question: do you know of any photographs
that show the shock-wave pattern generated by an SR-71? I can't imagine
that any exist, other than of wind-tunnel models, but the original
enquirer (on a.b.p.aviation) thinks so; what might he be thinking of?