In the lead up to Osama bin Laden having his head vented by Seal Team 6, his compound was monitored by a cadre of satellite-mounted hyperspectral imaging devices. These wide-band imagers are now being adapted for use in UAVs.
Essentially, a hyperspectral image is one derived of hundreds of spectral bands, taken simultaneously. These bands extend beyond the paltry "visible spectrum" that humans experience and include the near-infrared and shortwave infrared wavelengths. Every material will reflect these wavelengths differently, creating individual "spectral signatures." If the signature is recognized, the substance can be identified using as little as one pixel from the image. Per Raytheon:
For instance, operating in the shortwave infrared, hyperspectral sensors can distinguish between natural terrain and camouflage (indicating hidden objects) and identify areas of disturbed earth (indicating possible IEDs).
Originally developed as part of the ARTEMIS (Advanced Responsive Tactically Effective Military Imaging Spectrometer) satellite system, these sensors have been used by the Air Force since June of last year and can provide actionable intelligence to fighters on the ground within minutes of sensor tasking.
Now that they're being adapted for use in UAVs, including bigger optics and systems to compensate for atmospheric disturbances, these sensors could radically change the way UAV's are employed - in everything from legitmate crop monitoring and drug interdiction to identifying smugglers tunnels and the composition of haz-mat spills. Even if we can't see what's going on, these sensors will.