I seem to like responding to old posts.
As I understand, the speed of sound is not constant. What we refer to as the standard is a clear day at just above sea level.
Water slows it down. In acoustic sound management, it is block, reflect, reduce...
hard objects slow it down to a point where it can stop the sound wave. Living in an area which often has fog. i alway thought that sound carried better, more clear. Then, I learned that the moisture in the air actually dampens the sound slowing it down, and muting the softer background noise and this is why we think the sound is clearer.
I may not correctly understand your post. I like the photos. i am not the person to review them, my little sister is working on her Ph.d in Chicago. I have emailed the photos to her and will nag her, just out of curiosity.
Cheers