Why space matters: Imaging satellite operations, part 12—all the colors of the rainbow—from space!!!

This lesson is not about space Skittles.  Nor is it about any political parties or leanings within or without closets.

All the colors of the optical rainbow.
All the colors of the optical rainbow.

The one thing I am asking you to do for this and the remainder of these imagery operations lessons, is keep in mind I am guessing.  I don’t KNOW exactly how DigitalGlobe conducts their space operations.  But my guesses will be based on the documents which a company like DigitalGlobe puts out prolifically.  A little chest-pounding never hurt a company’s bottom-line, and DigitalGlobe has done its share, resulting in some great resources.

So, the satellite’s payload.  We will be focusing on DigitalGlobe’s assets.  It doesn’t hurt to remember that in Lesson 8, I mentioned DigitalGlobe has five satellites.  But they are five different satellites with five different imagery payloads:  IKONOS, GEOEYE-1, QuickBird, WorldView-1, and WorldView-2.

This conglomeration of a constellation exists because DigitalGlobe merged with another American imagery company called GeoEye earlier this year (2013).  There are more satellites projected to be launched next year (Worldview-3), but it’s good to remember the payloads, and perhaps the satellite busses, aren’t the same.

For our example, we will start with DigitalGlobe’s latest satellite, launched in 2009:  WorldView-2.  According to DigitalGlobe’s specifications for Worldview-2, it orbits 770 kilometers above the Earth (about 478 miles–low earth orbit, then), sun-synchronously.  If you need a refresher as to why that’s important, please read this lesson, then come on back.  Go on—take your time…

Now, back to the payload. We know, because DigitalGlobe tells us so, that WorldView-2’s payload is different from the other ones in their constellation.  They are so proud of it, it’s almost cute.  It is “the first high resolution 8-band multispectral commercial satellite.” (DG’s DS-WV206/13 Data Sheet)

Let’s clarify multispectral.  It’s an interesting term, because really it pertains to energy wavelengths—that is, very specific frequencies in the electromagnetic spectrum, including ones the unaided eye can’t see.  And of course name hints there is more than one frequency in which DigitalGlobe’s payload imager can take snapshots.  In this case, according to DigitalGlobe, these spectral bands are identified as 8 “colors:” blue, green, red, near-InfraRed1, coastal (?), yellow, red edge, and near-InfraRed2.

The payload is also panchromatic, meaning there is a very high resolution image sensor on board, too.  This one has more pixels on it than the multispectral sensor, with the ability to encompass a huge swath of the visible light spectrum in one image.  I won’t pretend to know how both sensors are mounted within the payload.

What do these mean, and how are these colors (spectral bands and panchromatic) used?  That’s for the next lesson!

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