Tethered balloons to carry meteorological instrumentation, and testing of small UAVs is what they do there. I believe that increasingly they're running LIDARS - upward facing laser instruments there as well.
Have I seen anything from the air? Nope.
Are they busy? - almost certainly from the fact that I'm regularly seeing, professionally, numerous results and papers from the research that they do there.
I certainly wouldn't risk flying through it - the odds of my not seeing what they do there, when they're doing it, are much too high for my taste.
G