Finally, we get to discuss the colors used for DigitalGlobe’s imagery satellites—or satellite, as we will be focusing (no pun intended—these satellites can’t really focus, remember) on WorldView-2.
According to DigitalGlobe’s Basic Imagery literature, WorldView-2’s image sensors use eight different colors to look at the Earth: Coastal, Blue, Green, Yellow, Red, Red Edge, Near-IR (InfraRed)1, and Near-IR2. These colors are why DigitalGlobe calls the satellite payload, multi-spectral capable. The satellite also can conduct a collection using a panchromatic (black and white) sensor (we discussed sensors in the previous lesson, remember? Please–go there and read if you don’t.). Each color is meant to help DigitalGlobe and its customers discover different features and activities on the Earth’s surface.
So, um, “coastal” is apparently a color (yeah—I haven’t heard of it either). Looking at another of their product brochures, “coastal” means coastal blue (page 21). Which makes sense, I guess, because the light wavelength band (396-458 nanometers) they associate it with edges right into the blue color wavelength band (starting at 442 nanometers).
WAIT—don’t run away!! I’m not going to talk about those numbers and terms here. If you want to learn more about light bands, wavelengths, nanometers, etc., then you will be motivated enough to click on this link, and maybe this one, to learn more. If you aren’t, ignore that and please continue reading. I’m trying to keep this in English-type speak—really!!
Suffice it to type that Coastal is a kind of blue. What is it used for? Well, according to this site, it’s used to help see into clear water—nearly 45 feet deep. So, the most prevalent areas where water is that shallow are the coasts. Voila—Coastal (I think). This color helps the camera show the sea/lake floors, submerged water plants, sediments (dirt, etc.) suspended in the water, and the cloudiness of the water. Click on this link, and then try this one, to see examples of a coastal image (I think—DigitalGlobe doesn’t really call the color out).
What does Coastal mean to you and why does it matter? Well, it probably won’t matter to you unless you’re working in these coastal areas. What it means to the person working along the coast is that in one quick sweep of WorldView 2’s sensor, it’s able to get a fairly accurate map of the seabed up to 45 feet deep. Here’s an example of how coastal blue can help with seeing the truth on the ground. So maybe something has changed along that seabed because of an earthquake, or flooding up the river—or a hurricane has submerged and moved objects hazardous to marine navigation. Maybe people need to know this kind of information as soon as possible. DigitalGlobe and other imagery companies like RapidEye can respond fairly quickly.
Compare this to sending out a boat or two to figure out what’s going on. Or sending an aircraft (which will likely have a better camera)—it may not be able to respond within the time that DigitalGlobe can—or the weather may still be too dangerous for either craft (air or sea). And both require their craft to move back and forth along the coastline to cover the area the WorldView-2’s camera covered in less than 10 minutes. Here are some examples of satellite collections of Hurricane Sandy’s handiwork (not necessarily using just coastal blue). Imagine trying to get all those pictures with a ship, airplane or drone! More Sandy images are here, too.
So area access and timeliness are two major advantages the satellite has over the terrestrial craft. These advantages are obviously inherent in satellites and satellite operations, not just the color band selected.
Okay, so that was a bit long—next lesson will be about blue, and if I don’t type too much, green, too.
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