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.