On Friday, September 8 at 3:23:37 AM,
three high school students (geocachers EricJD, Team 4 Larson and
wesman39) and I were near this exact spot. I was 50 feet away on
the road while the three students were spaced about 0.1 mile apart
down the road going westward. We hoped that at least one of us was
precisely where we needed to be to see a green flashing laser
(pulsing 20 times a second) emanating from the CALIPSO satellite
that was, for a split second, directly overhead at that time. On
that day and until this time, as far as I know, the green laser
from CALIPSO has only been seen by about three people on the entire
Earth.
So what is so special about this
satellite? It’s the only satellite that uses LIDAR instruments to
analyze the vertical structure and properties of thin clouds and
aerosols over the globe. LIDAR is an acronym for Light Detection
and Ranging; or Laser Imaging Detection and Ranging. CALIPSO uses
an infrared laser and a green laser to probe the atmosphere by
looking for two things, the amount of back scattering of its light
and how long it takes for the light to come back. We were looking
for the green one. The amount of backscatter tells a lot about the
quantity and size of the particles and the time delay of the
reflection enables it to determine the distance to the
particles.
For whatever reason we didn’t see it on
that morning. 
Like finding this cache, the
challenge is to get right on a spot that you know you need to
be by either using a GPS unit or an aerial image showing the
magic spot. To see it we had to be within a couple hundred
meters of being right under it, looking straight up and not
blinking. The green laser can be seen as a short beam when the
alignment is right. Only a few pulses are visible then it’s
gone!
The colorful image here shows a visual
display of the data gathered by CALIPSO on that early morning pass
over North America on September 8, 2006. Click on it to magnify it
a bit more. The red line depicts the coord we were at at the time
it passed overhead.
This shows the path it took over the North America and
here’s a map showing the track through Waterloo that it made
that morning.
One uncommon feature about this satellite
is that it is in a “sun synchronous” orbit. That means that it
comes over a certain area every so often at close to the exact same
time. I am very fortunate that it comes over so close to Waterloo.
Every 16 days, like clockwork, it comes back over this area. It is
drifting slightly eastward and is arriving slightly earlier each
time. I will holler here when I finally do see it!
On that early morning back in September
when I arrived near here with my dedicated students, we were
surprised by a very loud great horned owl hoot that was very close
to the car! Then, as I was folding up my tripod I was thinking
about how glad I was that the police didn’t stop by. But sure
enough, there he came, a police officer. That was the 13 ½ half
time I’ve been asked by the police what I am doing when I’m out and
about making some kind of observation or doing some kind of
experiment! Read about the ½ time
here.