Sifting the 'hyperspectral cube'
By scanning across a wide spectrum all at once across a wide area, it's then possible to use a powerful computer to crunch through all wavelengths coming from all points on the surface below (the so-called "hyperspectral cube", made up of the full spectrum coming from all points on a two-dimensional surface).
If the sensor is good enough and the computer crunching powerful and discriminating enough, the satellite can then identify a set of points on the surface where substances or objects of interest are to be found, and supply map coordinates for these. This is a tiny amount of data compared to the original "hyperspectral cube" generated by ARTEMIS and crunched by the satellite's onboard processors, and as such it can be downloaded to a portable ground terminal (rather than a one with a big high-bandwidth dish). Within ten minutes of the TacSat passing overhead, laptop-sized ROVER ground terminals can be marking points of interest on a map for combat troops nearby.
Exactly what sorts of objects and substances ARTEMIS is able to pick out of its region-spanning hyperspectral cubes is a military secret. However this briefing pdf given in 2006 by US airforce lab officials suggests that it was expected to pierce overhead camouflage that would deceive optical or thermal sensing; that it would be able to spot disturbed earth and "concealed adits" (that is cave or tunnel entrances invisible from above) and generally "detect and identify" unspecified "targets".
Evidently the TacSat-3 can do at least some of this, as we now learn that following a year as an experiment it has proved so successful that it is now being handed over to US air force Space Command to become a full-time operational asset - America's first hyperspectral spy sat.
"ARTEMIS can detect various man-made and natural materials, which adds a fundamentally new capability," according to Bill Hart, veep at ARTEMIS maker Raytheon.
TacSat-3 has "demonstrated the utility of hyperspectral information to benefit soldiers, sailors, airmen and Marines around the world," says Dr Peter Wegner, chief of the Operationally Responsive Space office at the Pentagon, in a statement issued yesterday.
It's quite unusual for a military prototype to be put straight into frontline service like this; furthermore we're told that ARTEMIS data has already been "used operationally" even while the TacSat-3 was under control of the airforce research lab.
All this would seem to indicate that hyperspectral spy sats are set to become a significant new player in the surveillance and spookery world. Even more than ever, you may watch the skies - but the skies will be watching you back. And you can forget about relying on your insulated camouflage netting or your overhung tunnel entrance which never shows a shadow, or your buried bomb or weapons cache. ARTEMIS and its successors will sniff you out, perhaps, even if thus far you have remained completely unseen.
There's more on the TacSat-3 here for those interested. ®