Hema’ehu needs to come clean with this first: I work with/for these guys, and the principal investigator paid my salary (when I used to ask for pay – he is now holding my graduate degree just out of reach to get me to finish), and I’m hoping to get back on the payroll come June. So is Hema’ehu sucking up? Heck yes. Is this thing still some of the coolest sh*t you’ll ever see? Double heck yes.
The Carnegie Airborne Observatory is a combination hyperspectral remote sensing instrument, LiDAR sensor, and geocorrectional device mounted onto an airplane. The hyperspectral scanner, AVIRIS (Airborne Visible-InfraRed Imaging Spectrometer) measures upwelling (reflected) radiation from the earth’s surface. As sunlight careens through the Earth’s atmosphere and hits the ground, it comes into contact with a huge range of materials: plant, animal, buildings, yo’ mama, etc. Every physical component, down to the very tiny elemental bonds that hold something together, either reflect, scatter, or absorb that sunlight. Because the solar spectrum is wide – we can see but a tiny portion of this spectrum with our eyes – the materials (in the parlance of remote sensing, ground cover) have distinctive and unique spectral signatures due to the difference in reflection, scattering, and absorption of light at all wavelengths along the solar spectrum. So AVIRIS measures that stuff.
This is known as a passive remote sensing instrument. It merely collects information about light attenuation at an assortment of wavelengths from sunlight bounced off the Earth. The LiDAR (Light Detection And Ranging), conversely, is an active remote sensing instrument. Similar to ship sonars (or, for that matter, killer dolphin sonars) or the po-po’s speed gun, the LiDAR shoots out a beam of energy that bounces off the ground cover and returns to the airplane lickety-split. The time it takes the beam to hit the ground and return gives the height of the ground at that spot. So LiDAR measures height.
The on-board GPS thing is cool, too, but for more nerdy, less applicable and interesting reasons. It tells the computer on board exactly where the airplane is in three-dimensional space as it flies over the Earth. Hema’ehu would be the first to agree that this does not seem so hard, as we can all see airplanes as they fly over head. Please trust that this instrument is very precise, however, and this precision makes most remote sensing scientists drool.
The combination of hyperspectral scanner and LiDAR sensor gives an extremely high-definition image of some segment of the planet. Chris Field, the director of the Carnegie Institution Department of Global Ecology, compared the CAO’s performance to that of a “CAT-scan of Earth.”