Residents of the Canaries could be forgiven for thinking they were under attack from an alien race over the last two weeks, as the islands played host to a European Space Agency test of a laser tracking system for greenhouse gases. Infrared laser experiment for studying greenhouse gases Infrared laser experiment for studying …
They're used to it
They've been using lasers from the observatories in the canaries for some time now,
such as from the Isaac Newton telescope there:
The lasers are used to create an "artificial star" in the field of view of the telescope by fluorescing sodium atoms in the upper atmosphere (you need a bright star in the image to align the optics with).
Newer telescope plans have lots of laser stars (10-20) and beams, e.g. for the EELT (42m) telescope that ESO is building.
They've been doing this between water towers in Northamptonshire lately (10 miles or more per side of a triangle), although I don't think that it had anything to do with scientific or in-any-way useful matters.
An arts project I think, probably paid for out of my taxes :-(
or communicating with aliens
"a laser tracking system for greenhouse gases"
Well, that's what they *say* it's for...!